ww/selfhost/cmd/w6a/main.combined.ww

// time — clocks, instants, durations. Mirrors Hare's lib/time
// (ref/hare/time/duration.ha, instant.ha, arithm.ha,
// +linux/functions.ha). Calendar / date / strftime / timezone /
// sleep live in separate Hare modules and graduate when callers /
// supporting stdlib arrive.
//
// `duration` is a NAMED alias of i64 (lib/math/random precedent
// at lib/math/random/random.ww:8); ww treats NAMED as a newtype,
// so cross-i64 arithmetic inside this module needs explicit casts.
// Hare's structural alias semantics let those casts vanish, but
// our type checker is strict.

package time;

@symbol("rt_syscall") fn syscall2(num: i64, a: i64, b: i64) i64;

def SYS_CLOCK_GETTIME: i64 = 228;

// ref/hare/time/duration.ha:6. 290y representable range.
export type duration = i64;

// ref/hare/time/duration.ha:9-18. Plan-9 naming (lowercase)
// diverges from Hare's uppercase per project rule 4.
export def nanosecond:  duration = 1i64;
export def microsecond: duration = 1000i64;
export def millisecond: duration = 1000000i64;
export def second:      duration = 1000000000i64;

// ref/hare/time/instant.ha:9. (sec, nsec) pair — NOT POSIX struct
// timespec (which uses u32 nsec). Layout matches Linux's struct
// timespec on 64-bit (i64+i64) so we can pass &instant directly
// to clock_gettime.
export type instant = struct {
	sec:  i64,
	nsec: i64,
};

// ref/hare/time/+linux/functions.ha:84. First cut exposes only
// realtime and monotonic; Hare's process_cpu / thread_cpu / boot /
// realtime_alarm / boot_alarm / tai graduate when a caller needs
// them (CLAUDE.md rule 9 — Hare-fidelity, no premature surface).
export type clock = enum i32 {
	realtime  = 0,
	monotonic = 1,
};

// ref/hare/time/+linux/functions.ha:138. Hare's now() also aborts
// on impossible errnos. (instant | oserror) is deliberately not
// the return shape — EINVAL / EFAULT are programmer errors (bad
// clock id, bad ptr), and a 1-word-payload sum return walks into
// task #9's cgen-divergence trap.
export fn now(c: clock) instant = {
	let i: instant;
	let rc = syscall2(SYS_CLOCK_GETTIME, (c as i32): i64, (&i): i64);
	if (rc != 0i64) { abort("time.now: clock_gettime failed"); };
	return i;
};

// ref/hare/time/arithm.ha:9. Adds duration to instant. The
// negative-duration branch normalises nsec into [0, second).
export fn add(i: instant, x: duration) instant = {
	let r: instant;
	let xi: i64 = x: i64;
	let sec: i64 = second: i64;
	let nsec: i64 = nanosecond: i64;
	if (xi == 0i64) {
		r.sec  = i.sec;
		r.nsec = i.nsec;
		return r;
	};
	if (xi > 0i64) {
		r.sec  = i.sec + (i.nsec + xi) / sec;
		r.nsec = (i.nsec + xi) % sec;
		return r;
	};
	r.sec  = i.sec + (i.nsec + xi - sec + nsec) / sec;
	r.nsec = (i.nsec + (xi % sec) + sec) % sec;
	return r;
};

// ref/hare/time/arithm.ha:26. Returns duration from a to b.
// Sign convention: b - a.
export fn diff(a: instant, b: instant) duration = {
	let sec: i64 = second: i64;
	let v: i64 = ((b.sec - a.sec) * sec) + (b.nsec - a.nsec);
	return v: duration;
};

// ref/hare/time/arithm.ha:32. -1 if a < b, 0 if equal, +1 if a > b.
export fn compare(a: instant, b: instant) i8 = {
	if (a.sec  < b.sec)  { return -1i8; };
	if (a.sec  > b.sec)  { return  1i8; };
	if (a.nsec < b.nsec) { return -1i8; };
	if (a.nsec > b.nsec) { return  1i8; };
	return 0i8;
};

// os — process and filesystem facade. The body of each call lands
// either in libwwrt.a (rt_syscall trampoline) or libc bindings,
// depending on how the program was linked.

package os;

import time;

@symbol("rt_syscall") fn syscall0(num: nr) i64;
@symbol("rt_syscall") fn syscall1(num: nr, a: i64) i64;
@symbol("rt_syscall") fn syscall2(num: nr, a: i64, b: i64) i64;
@symbol("rt_syscall") fn syscall3(num: nr, a: i64, b: i64, c: i64) i64;
@symbol("rt_syscall") fn syscall4(num: nr, a: i64, b: i64, c: i64, d: i64) i64;

@symbol("rt_free")  export fn free(p: *void, n: u64) void;

// Linux amd64 syscall numbers. Internal to this module — passed as
// the first arg of syscall0..4 via libwwrt's rt_syscall trampoline.
// `nr` is the type so the call sites can't accidentally pass an
// arbitrary i64 (`syscall1(0i64, ...)` no longer typechecks).
type nr = enum i64 {
	READ        = 0,
	WRITE       = 1,
	OPEN        = 2,
	CLOSE       = 3,
	LSEEK       = 8,
	ACCESS      = 21,
	DUP2        = 33,
	GETPID      = 39,
	FORK        = 57,
	EXECVE      = 59,
	EXIT        = 60,
	WAIT4       = 61,
	MKDIR       = 83,
	RMDIR       = 84,
	UNLINK      = 87,
	GETCWD      = 79,
	GETDENTS64  = 217,
	NEWFSTATAT  = 262,
};

// open(2) flags. Linux values, matching <fcntl.h>. Hare names them
// `fs::flag::RDONLY` etc; we use the same leaf names so callers say
// `os.flag.RDONLY` and `os.flag.WRONLY | os.flag.CREATE`.
export type flag = enum i32 {
	RDONLY  = 0,
	WRONLY  = 1,
	RDWR    = 2,
	CREATE  = 64,	// 0x40
	EXCL    = 128,	// 0x80 — pair with CREATE to fail on existing path
	TRUNC   = 512,	// 0x200
};

// lseek(2) whence. Hare names it `io::whence`.
export type whence = enum i32 {
	SET = 0,
	CUR = 1,
	END = 2,
};

export fn exit(code: i32) void = {
	syscall1(nr.EXIT, code: i64);
};

// PATH_MAX / pathbuf / kpath — port of Hare's ref/hare/sys/+linux/
// syscalls.ha:25,27,29-55. Hare's `path` accepts a sum `(str |
// []u8 | *const u8)`; ww's lib/os public surface narrows to `str`
// (the Hare-faithful surface at ref/hare/os/os.ha:37,47,50 etc).
// Internally, [[kpath]] copies the `str` bytes into a single
// module-level [[pathbuf]] scratch slot and NUL-terminates so the
// raw Linux syscalls (which require C strings) see a valid
// terminator. Same precedent as Hare's static `pathbuf`.
//
// Non-reentrant: one buffer, every [[stat]] / [[open]] / etc.
// rewrites it. Same caveat as strconv's `*tos` family (overwritten
// on next call). Caller must NOT hold a kpath-returned pointer
// across another lib/os path call. Graduates when ww grows a
// thread story.
//
// `nil`-as-overflow over `(*u8 | oserror)`: wwstage over-allocates
// 1-word-payload tagged returns to 24B (cstage emits 16B).
// Task #9; revert at task #10 when fixed. Repro at
// .ai/probe_tagged_return_pointer_payload.ww.
export def PATH_MAX: i32 = 4096;
let pathbuf: [4096]u8;

// ref/hare/sys/+linux/types.ha:886-888. ww folds `sys` into `os`, so the
// std fd NUMBERS live here (the sys role). Typed i32, NOT io.file as in
// Hare's os::stdout_file (ref/hare/os/+linux/stdfd.ha:28): Hare's `os`
// imports `io`, but ww's `os` is the import floor and must never import
// io (lib/CLAUDE.md) — so the io.file/io.handle binding can't live here.
// Consumers (lib/fmt's stdio wrappers) cast i32→io.file at the use site,
// where the handle layer is already in scope.
export def STDIN_FILENO:  i32 = 0;
export def STDOUT_FILENO: i32 = 1;
export def STDERR_FILENO: i32 = 2;

fn kpath(p: str) *u8 = {
	if (p.len + 1 >= PATH_MAX) { return nil: *u8; };	// ENAMETOOLONG
	let i: i32 = 0;
	for (i < p.len) { pathbuf[i] = p[i]; i += 1; };
	pathbuf[p.len] = 0u8;
	return &pathbuf[0];
};

// Raw, non-fallible primitives. These return Linux's int conventions
// (negative = -errno, non-negative = bytes/fd/etc). Callers wanting a
// Hare-style fallible API use the wrappers below.
export fn write(fd: i32, buf: *u8, n: u64) i64 = {
	return syscall3(nr.WRITE, fd: i64, buf: i64, n: i64);
};

export fn read(fd: i32, buf: *u8, n: u64) i64 = {
	return syscall3(nr.READ, fd: i64, buf: i64, n: i64);
};

export fn close(fd: i32) i32 = {
	return syscall1(nr.CLOSE, fd: i64): i32;
};

// dup2(2): make `newfd` refer to the same description as `oldfd`,
// closing `newfd` first if open. Returns `newfd` on success or a
// negative errno. Used by w6c_ww to redirect stdout into an output
// file without changing the cgen emit path.
export fn dup2(oldfd: i32, newfd: i32) i32 = {
	return syscall2(nr.DUP2, oldfd: i64, newfd: i64): i32;
};

// Fallible wrappers. The error variant is `oserror` (an i64 carrying
// -errno). The sum type makes success/failure explicit and lets
// callers `?` the result up the stack.
export fn tryread(fd: i32, buf: *u8, n: u64) (i64 | oserror) = {
	let r: i64 = read(fd, buf, n);
	if (r < 0) { return r: oserror; };
	return r;
};

export fn trywrite(fd: i32, buf: *u8, n: u64) (i64 | oserror) = {
	let r: i64 = write(fd, buf, n);
	if (r < 0) { return r: oserror; };
	return r;
};

// open — Linux open(2). Returns -errno on failure, fd otherwise.
// Higher-level callers prefer `tryopen`. Mirrors Hare's os::open
// (ref/hare/os/os.ha:117); kpath lands the bytes in pathbuf.
// Returns -ENAMETOOLONG (-36) if the path overflows PATH_MAX.
export fn open(path: str, flags: flag, mode: i32) i32 = {
	let p: *u8 = kpath(path);
	if (p == nil: *u8) { return -36i32; };	// ENAMETOOLONG
	return syscall3(nr.OPEN, p: i64, (flags as i32): i64, mode: i64): i32;
};

export fn tryopen(path: str, flags: flag, mode: i32) (i32 | oserror) = {
	let fd: i32 = open(path, flags, mode);
	if (fd < 0) { return fd: i64: oserror; };
	return fd;
};

// lseek — set/inspect the fd's position. Returns the new offset or
// a negative errno. We use this for fstat-free file-size discovery
// (open ⇒ lseek to end ⇒ lseek back).
export fn lseek(fd: i32, off: i64, w: whence) i64 = {
	return syscall3(nr.LSEEK, fd: i64, off, (w as i32): i64);
};

// oserror — the underlying errno from a failed syscall, as a
// negative i64 (Linux's int convention; e.g. -2 = ENOENT). The
// `!`-flagged alias makes ?-propagation pick this variant as the
// error half of any (T | oserror) shape. Hare's analogue is
// errors::errno carried inside io::error.
export type oserror = !i64;

// errno — the raw Linux errno as a positive code (ref/hare/sys/+linux/
// errno.ha:5, `errno = !int`). ww folds Hare's `sys` role into os
// (lib/CLAUDE.md), so the sys::errno machinery lands here. Spelled i32
// rather than int: Linux errnos are kernel ints (32-bit), keeping os's
// kernel-facing surface uniformly i32. Distinct from [[oserror]] (!i64,
// the syscall's *negative* raw return) — the two model different
// things, so they are not unified; the negative→positive normalization
// lives at the oserror→errors.error boundary in those callers.
export type errno = !i32;

// Mapped errno values, ref/hare/sys/+linux/errno.ha:559-682. Positive,
// matching Hare's defs (the kernel returns -N; the wrap-to-positive is
// the caller's concern). Subset: exactly the errnos [[errors.errno]]
// maps to a named condition; grow as callers surface more.
export def ENOENT:       errno = 2;
export def EINTR:        errno = 4;
export def EAGAIN:       errno = 11;
export def EACCES:       errno = 13;
export def EBUSY:        errno = 16;
export def EEXIST:       errno = 17;
export def EINVAL:       errno = 22;
export def EOVERFLOW:    errno = 75;
export def ENETUNREACH:  errno = 101;
export def ETIMEDOUT:    errno = 110;
export def ECONNREFUSED: errno = 111;
export def ECANCELED:    errno = 125;

// strerror — human-readable text for an [[errno]] (Hare's
// sys::strerror, ref/hare/sys/+linux/errno.ha:18). FAITHFUL MINIMAL
// SUBSET: the mapped errnos above plus a generic fallback; grow the
// switch as callers surface more (lib/CLAUDE.md documented-subset, not
// a workaround). Messages verbatim from the reference. Hare's
// unknown_errno formats the numeric value; that is deferred.
export fn strerror(err: errno) str = {
	switch (err) {
	case ENOENT:       return "No such file or directory";
	case EINTR:        return "Interrupted system call";
	case EAGAIN:       return "Resource temporarily unavailable";
	case EACCES:       return "Permission denied";
	case EBUSY:        return "Device or resource busy";
	case EEXIST:       return "File exists";
	case EINVAL:       return "Invalid argument";
	case EOVERFLOW:    return "Value too large for defined data type";
	case ENETUNREACH:  return "Network is unreachable";
	case ETIMEDOUT:    return "Connection timed out";
	case ECONNREFUSED: return "Connection refused";
	case ECANCELED:    return "Operation canceled";
	};
	return "Unknown error";
};

// filesize — byte length of an open fd via lseek-to-end-and-back.
export fn filesize(fd: i32) (i64 | oserror) = {
	let end: i64 = lseek(fd, 0i64, whence.END);
	if (end < 0) { return end: oserror; };
	let r: i64 = lseek(fd, 0i64, whence.SET);
	if (r < 0) { return r: oserror; };
	return end;
};

// readall — keep reading until `n` bytes have arrived or the fd
// closes early. Hare name (io::readall); the buffer is caller-
// supplied, matching the Plan 9 subset convention.
export fn readall(fd: i32, buf: *u8, n: u64) (i64 | oserror) = {
	let got: u64 = 0u64;
	for (got < n) {
		let r: i64 = read(fd, buf + got, n - got);
		if (r < 0) { return r: oserror; };
		if (r == 0) { return got: i64; };	// short read: caller decides
		got += r: u64;
	};
	return got: i64;
};

// writeall — keep writing until `n` bytes have been accepted or the
// fd refuses progress. Hare name (io::writeall).
export fn writeall(fd: i32, buf: *u8, n: u64) (i64 | oserror) = {
	let sent: u64 = 0u64;
	for (sent < n) {
		let r: i64 = write(fd, buf + sent, n - sent);
		if (r < 0) { return r: oserror; };
		if (r == 0) { return sent: i64; };
		sent += r: u64;
	};
	return sent: i64;
};

// ---- process and filesystem helpers used by the `ww` driver ----------

// access(2): returns 0 if the file is reachable, negative errno
// otherwise. mode is the bitset described in <unistd.h> (F_OK=0).
// Mirrors Hare's os::access (ref/hare/os/+linux/fs.ha:access).
// Returns -ENAMETOOLONG (-36) if the path overflows PATH_MAX.
export fn access(path: str, mode: i32) i32 = {
	let p: *u8 = kpath(path);
	if (p == nil: *u8) { return -36i32; };
	return syscall2(nr.ACCESS, p: i64, mode: i64): i32;
};

// remove — unlink(2). Mirrors Hare's os::remove
// (ref/hare/os/os.ha:12).
export fn remove(path: str) i32 = {
	let p: *u8 = kpath(path);
	if (p == nil: *u8) { return -36i32; };
	return syscall1(nr.UNLINK, p: i64): i32;
};

// mkdir — mkdir(2). Mode is the unix permission bitset (e.g. 0o700).
// Returns 0 on success, negative errno otherwise. Mirrors Hare's
// os::mkdir (ref/hare/os/os.ha:50).
export fn mkdir(path: str, mode: i32) i32 = {
	let p: *u8 = kpath(path);
	if (p == nil: *u8) { return -36i32; };
	return syscall2(nr.MKDIR, p: i64, mode: i64): i32;
};

// rmdir — rmdir(2). Mirrors Hare's os::rmdir
// (ref/hare/os/os.ha:58).
export fn rmdir(path: str) i32 = {
	let p: *u8 = kpath(path);
	if (p == nil: *u8) { return -36i32; };
	return syscall1(nr.RMDIR, p: i64): i32;
};

// mkdirs — recursive mkdir. Creates `path` and any non-existent
// parent directories with the given mode. EEXIST is silently
// accepted (matches Hare's `errors::exists` skip in os::mkdirs);
// any other syscall failure surfaces as `oserror`.
//
// Mirrors Hare's os::mkdirs (ref/hare/os/os.ha:54). The in-place
// '/' → NUL splice walks the kpath-loaded [[pathbuf]] directly
// instead of recursing through [[mkdir]] — re-entering kpath would
// clobber the buffer mid-walk (single static slot, see kpath's
// non-reentrancy note above).
export fn mkdirs(path: str, mode: i32) (void | oserror) = {
	let cp: *u8 = kpath(path);
	if (cp == nil: *u8) { return -36i64: oserror; };
	let n: i32 = path.len;
	if (n == 0) { return; };

	// Walk forward; at each '/' boundary, NUL-terminate the prefix,
	// raw MKDIR syscall on pathbuf, restore the slash, continue.
	// Skip index 0 so a leading '/' on absolute paths doesn't
	// trigger an empty mkdir.
	let i: i32 = 1;
	for (i < n) {
		if (pathbuf[i] == '/') {
			pathbuf[i] = 0u8;
			let r: i32 = syscall2(nr.MKDIR,
			    (&pathbuf[0]): i64, mode: i64): i32;
			pathbuf[i] = 47u8;
			if (r < 0) {
				if (r != -17) { return r: i64: oserror; };
			};
		};
		i += 1;
	};

	let r: i32 = syscall2(nr.MKDIR,
	    (&pathbuf[0]): i64, mode: i64): i32;
	if (r < 0) {
		if (r != -17) { return r: i64: oserror; };
	};
	return;
};

// getpid(2). Used by the driver to mint unique scratch paths.
export fn getpid() i32 = {
	return syscall0(nr.GETPID): i32;
};

// fork(2): 0 in the child, child pid in the parent, negative errno
// on failure.
export fn fork() i32 = {
	return syscall0(nr.FORK): i32;
};

// execve(2): on success, does not return. Mirrors Hare's
// os::exec::exec path arg (str). argv/envp stay `**u8` — the
// kernel takes a NUL-pointer-terminated table of NUL-terminated
// C strings, a different shape from a path.
export fn execve(path: str, argv: **u8, envp: **u8) i32 = {
	let p: *u8 = kpath(path);
	if (p == nil: *u8) { return -36i32; };
	return syscall3(nr.EXECVE, p: i64, argv: i64, envp: i64): i32;
};

// wait4(2): wait for `pid` (or any child if -1), store status in
// `*status`, return the pid that ended (or negative errno).
export fn wait4(pid: i32, status: *i32, options: i32, rusage: *void) i32 = {
	return syscall4(nr.WAIT4, pid: i64, status: i64,
	    options: i64, rusage: i64): i32;
};

// getcwd(2) — Linux flavour. Writes the NUL-terminated cwd into `buf`
// and returns the number of bytes written (including the NUL), or a
// negative errno. The driver uses it to expand `.` to the cwd's
// basename for `ww build` / `ww test`.
export fn getcwd(buf: *u8, n: u64) i64 = {
	return syscall2(nr.GETCWD, buf: i64, n: i64);
};

// getdents64(2) — Linux directory enumeration. The fd must be opened
// with O_RDONLY on a directory. `buf` receives a packed sequence of
// linux_dirent64 records:
//
//   struct linux_dirent64 {
//       u64  d_ino;       // 0..7
//       i64  d_off;       // 8..15
//       u16  d_reclen;    // 16..17  — total bytes for this record
//       u8   d_type;      // 18      — DT_REG/DT_DIR/...
//       u8   d_name[];    // 19..    — NUL-terminated name + padding
//   };
//
// Returns bytes written into `buf` (advance by d_reclen to walk),
// 0 at end-of-directory, or a negative errno.
export fn getdents64(fd: i32, buf: *u8, n: u64) i64 = {
	return syscall3(nr.GETDENTS64, fd: i64, buf: i64, n: i64);
};

// ---- environment ------------------------------------------------------

// rt_envp — runtime-side getter. rt/start.s captures envp into a DATAW
// slot before calling main; this binding lifts the captured pointer
// into ww. Same FFI shape as rt_syscall / rt_malloc / rt_abort: a TEXT
// symbol the linker resolves. The returned `**u8` is a NUL-terminated
// table of `*u8` entries, each pointing at a NUL-terminated
// "NAME=VALUE" byte sequence.
//
// We don't expose `rtenvp` directly; [[getenv]] is the only consumer.
@symbol("rt_envp") fn rtenvp() **u8;

// getenv — POSIX getenv. Returns a borrowed `str` view over the value
// bytes of the named environment variable, or void if the name is not
// present. The view is valid for the process lifetime — the bytes
// live in the kernel-supplied envp table at process entry. A future
// `setenv` (separate task) that grows the table behind the scenes
// would invalidate prior views; v1 has no setenv, so callers can
// hold the view indefinitely.
//
// Mirrors Hare's os::tryenv shape (returns void rather than panicking
// on missing). Hare also ships os::getenv (`(str | void)`) and
// os::mustenv (panic-on-missing); ww collapses to the single
// `(str | void)` form for now — consumers wanting "must" semantics
// abort at the call site.
//
// Algorithm: walk the NUL-pointer-terminated `environ` table doing a
// "name=" prefix match against each entry, byte-wise. NUL inside
// `name` would never match a real env var (env var names cannot
// contain '\0'), so we don't filter — POSIX puts that responsibility
// on the caller.
export fn getenv(name: str) (str | void) = {
	let envp: **u8 = rtenvp();
	let i: i32 = 0;
	for (true) {
		let entry: *u8 = envp[i];
		if (entry == nil: *u8) { return; };
		let j: i32 = 0;
		let matched: bool = true;
		for (j < name.len) {
			if (entry[j] == 0u8) { matched = false; break; };
			if (entry[j] != name[j]) { matched = false; break; };
			j += 1;
		};
		if (matched) {
			if (entry[name.len] == '=') {
				let val: *u8 = entry + ((name.len + 1): u64);
				let n: i32 = 0;
				for (val[n] != 0u8) { n += 1; };
				let r: str;
				r.ptr = val;
				r.len = n;
				return r;
			};
		};
		i += 1;
	};
	return;
};

// ---- stat / lstat / fstat / exists -----------------------------------
//
// Ports of Hare's stat family (ref/hare/fs/fs.ha:172,196 +
// ref/hare/sys/+linux/stat.ha:24-58). The Hare surface returns
// `filestat` by value; ww's cgreturn ABI tops out at 24B today (see
// STATUS task #21) and filestat is 80B, so [[stat]] / [[lstat]] /
// [[fstat]] take an out-parameter and return `(void | oserror)`.
// Re-evaluate the by-value shape when full sret lands.
//
// `filestat`, `mode`, and `stat_mask` live in lib/os because ww has
// no lib/fs yet; Hare puts them in `fs::`. These types graduate to
// lib/fs when that module ships — callers should expect a future
// re-export.
//
// Underlying syscall is SYS_newfstatat (262), which unifies
// stat/lstat/fstat through the `dirfd + flags` triple:
//   stat  = newfstatat(AT_FDCWD, path,  0)
//   lstat = newfstatat(AT_FDCWD, path,  AT_SYMLINK_NOFOLLOW)
//   fstat = newfstatat(fd,       "",    AT_EMPTY_PATH)
// Avoiding SYS_statx — its 256B variable layout would buy btime,
// but Hare's filestat doesn't expose btime either, so we stay on
// the simpler 144B kernel struct.

// fstatat(2) flag values. Linux constants from <linux/fcntl.h>.
// Names mirror Hare's ref/hare/sys/+linux/types.ha:45-51 (capital-
// AT_ prefix, top-level `def`s).
export def AT_FDCWD:            i32 = -100;
export def AT_SYMLINK_NOFOLLOW: i32 = 256;	// 0x100
export def AT_EMPTY_PATH:       i32 = 4096;	// 0x1000

// mode — file-mode bits. Mirrors Hare's fs::mode (ref/hare/fs/
// types.ha:63). Permission bits are the standard Unix octal subset;
// type bits live in the S_IFMT = 0o170000 region. Type-bit test:
//
//   let t: u32 = (fi.mode as u32) & 61440u32;	// 0o170000 mask
//   if (t == os.mode.DIR as u32) { /* directory */ };
//
// Numeric values are octal in Hare's source; ww has no octal
// literals so they're written as decimal with the octal in a
// trailing comment.
export type mode = enum u32 {
	// permission bits
	USER_RWX  = 448u32,	// 0o700
	USER_RW   = 384u32,	// 0o600
	USER_RX   = 320u32,	// 0o500
	USER_R    = 256u32,	// 0o400
	USER_W    = 128u32,	// 0o200
	USER_X    = 64u32,	// 0o100
	GROUP_RWX = 56u32,	// 0o070
	GROUP_RW  = 48u32,	// 0o060
	GROUP_RX  = 40u32,	// 0o050
	GROUP_R   = 32u32,	// 0o040
	GROUP_W   = 16u32,	// 0o020
	GROUP_X   = 8u32,	// 0o010
	OTHER_RWX = 7u32,	// 0o007
	OTHER_RW  = 6u32,	// 0o006
	OTHER_RX  = 5u32,	// 0o005
	OTHER_R   = 4u32,	// 0o004
	OTHER_W   = 2u32,	// 0o002
	OTHER_X   = 1u32,	// 0o001
	SETUID    = 2048u32,	// 0o4000
	SETGID    = 1024u32,	// 0o2000
	STICKY    = 512u32,	// 0o1000
	// file-type bits (S_IFMT mask = 0o170000 = 61440)
	UNKNOWN   = 0u32,
	FIFO      = 4096u32,	// 0o010000
	CHR       = 8192u32,	// 0o020000
	DIR       = 16384u32,	// 0o040000
	BLK       = 24576u32,	// 0o060000
	REG       = 32768u32,	// 0o100000
	LINK      = 40960u32,	// 0o120000
	SOCK      = 49152u32,	// 0o140000
};

// stat_mask — which filestat fields the call populated. Mirrors
// Hare's fs::stat_mask (ref/hare/fs/types.ha:129). newfstatat fills
// every field, so [[stat]] / [[lstat]] / [[fstat]] always set all
// seven bits OR-folded (see [[fillfilestat]]); per-bit testing is
// the documented sparse-backend pattern (cf. Hare's fs::fs network
// backends that only populate mtime+size).
export type stat_mask = enum u32 {
	UID   = 1u32,
	GID   = 2u32,
	SIZE  = 4u32,
	INODE = 8u32,
	ATIME = 16u32,
	MTIME = 32u32,
	CTIME = 64u32,
};

// filestat — Hare's fs::filestat (ref/hare/fs/types.ha:141). 80
// bytes. Times are time.instant (ref/hare/time/instant.ha:9) — the
// canonical Hare shape. See module-header note re: graduation to
// lib/fs.
export type filestat = struct {
	mask:  stat_mask,	// 0  (4)
	mode:  mode,		// 4  (4)
	uid:   u32,		// 8  (4)
	gid:   u32,		// 12 (4)
	sz:    u64,		// 16 (8)
	inode: u64,		// 24 (8)
	atime: time.instant,	// 32 (16)
	mtime: time.instant,	// 48 (16)
	ctime: time.instant,	// 64 (16) — ends at 80
};

// kstat — x86_64 kernel `struct stat` layout. Mirrors
// arch/x86/include/uapi/asm/stat.h (`__kernel_ulong_t`-keyed
// fields). 144 bytes. Module-internal; SYS_newfstatat writes into
// this buffer and the public stat fns then copy the bits into the
// Hare-shaped [[filestat]].
type kstat = struct {
	dev:        u64,	// 0
	ino:        u64,	// 8
	nlink:      u64,	// 16
	mode:       u32,	// 24
	uid:        u32,	// 28
	gid:        u32,	// 32
	pad0:       u32,	// 36
	rdev:       u64,	// 40
	sz:         i64,	// 48
	blksize:    i64,	// 56
	blocks:     i64,	// 64
	atime_sec:  i64,	// 72
	atime_nsec: i64,	// 80
	mtime_sec:  i64,	// 88
	mtime_nsec: i64,	// 96
	ctime_sec:  i64,	// 104
	ctime_nsec: i64,	// 112
	unused0:    i64,	// 120
	unused1:    i64,	// 128
	unused2:    i64,	// 136 — ends at 144
};

// emptypath — single-NUL byte used as the `pathname` arg to
// newfstatat with AT_EMPTY_PATH. The kernel requires a non-NULL
// pointer to a zero-length C string, NOT a null pointer. Bytes are
// read-only from the kernel's view; ww has no module-level const so
// this is a writable `let`.
let emptypath: [1]u8 = [0u8];

// fillfilestat — copy a 144B kstat into the 80B Hare-shaped
// filestat. Internal helper used by all three public entry points.
// Mirrors Hare's st_to_filestat (ref/hare/os/+linux/dirfdfs.ha:259):
// newfstatat populates every field, so the mask is the OR-fold of
// all seven Hare stat_mask bits.
fn fillfilestat(out: *filestat, k: *kstat) void = {
	out.mask        = stat_mask.UID | stat_mask.GID | stat_mask.SIZE
	    | stat_mask.INODE | stat_mask.ATIME | stat_mask.MTIME
	    | stat_mask.CTIME;
	out.mode        = k.mode: mode;
	out.uid         = k.uid;
	out.gid         = k.gid;
	out.sz          = k.sz: u64;
	out.inode       = k.ino;
	out.atime.sec   = k.atime_sec;
	out.atime.nsec  = k.atime_nsec;
	out.mtime.sec   = k.mtime_sec;
	out.mtime.nsec  = k.mtime_nsec;
	out.ctime.sec   = k.ctime_sec;
	out.ctime.nsec  = k.ctime_nsec;
};

// stat — fill *out with metadata for `path`. Follows symlinks.
// Returns ENAMETOOLONG (-36) as `oserror` if the path overflows
// PATH_MAX.
//
// Mirrors Hare's sys::stat (ref/hare/sys/+linux/stat.ha:51) modulo
// the out-param shape forced by the cgreturn 24B cap. Note: Hare's
// higher-level fs::stat (ref/hare/fs/fs.ha:172) instead has lstat
// semantics — we follow sys::stat's POSIX-stat behavior here.
export fn stat(out: *filestat, path: str) (void | oserror) = {
	let cp: *u8 = kpath(path);
	if (cp == nil: *u8) { return -36i64: oserror; };
	let k: kstat;
	let r: i64 = syscall4(nr.NEWFSTATAT,
	    AT_FDCWD: i64, cp: i64, (&k): i64, 0i64);
	if (r < 0) { return r: oserror; };
	fillfilestat(out, &k);
};

// lstat — like [[stat]] but does NOT follow a terminal symlink.
// Mirrors Hare's sys::lstat (ref/hare/sys/+linux/stat.ha:57).
export fn lstat(out: *filestat, path: str) (void | oserror) = {
	let cp: *u8 = kpath(path);
	if (cp == nil: *u8) { return -36i64: oserror; };
	let k: kstat;
	let r: i64 = syscall4(nr.NEWFSTATAT,
	    AT_FDCWD: i64, cp: i64, (&k): i64,
	    AT_SYMLINK_NOFOLLOW: i64);
	if (r < 0) { return r: oserror; };
	fillfilestat(out, &k);
};

// fstat — like [[stat]] but addresses the file by fd. Uses
// newfstatat(fd, "", AT_EMPTY_PATH); the kernel resolves the fd
// directly. Mirrors Hare's sys::fstat (ref/hare/sys/+linux/stat.ha:54).
export fn fstat(out: *filestat, fd: i32) (void | oserror) = {
	let k: kstat;
	let r: i64 = syscall4(nr.NEWFSTATAT,
	    fd: i64, (&emptypath[0]): i64, (&k): i64,
	    AT_EMPTY_PATH: i64);
	if (r < 0) { return r: oserror; };
	fillfilestat(out, &k);
};

// exists — true if `path` resolves to anything (regular file,
// directory, symlink, ...). Stat-shaped (Hare's `fs::exists`,
// ref/hare/fs/fs.ha:196) — no separate syscall. Symlinks are
// followed; a dangling symlink is `false`. ENAMETOOLONG is
// swallowed as `false` — Hare's os::exists doc says "true if a
// node exists at the given path, or false if not."
//
// Race warning: prefer "open and handle the error" over "exists
// then open" in real code (Hare's docstring carries the same
// note). The race is unavoidable in this shape.
//
// Goes through SYS_newfstatat directly rather than match'ing on
// [[stat]]'s `(void | oserror)` return. Functionally identical;
// the direct shape sidesteps a cstage/wwstage cgen disagreement
// on the slot size of `(void | oserror)` (cstage 16B, wwstage 24B
// — same class as STATUS #22, surfaced first time a match on this
// shape combined with an 80B local-struct local frame). Use the
// match shape once #22 lands.
export fn exists(path: str) bool = {
	let cp: *u8 = kpath(path);
	if (cp == nil: *u8) { return false; };
	let k: kstat;
	let r: i64 = syscall4(nr.NEWFSTATAT,
	    AT_FDCWD: i64, cp: i64, (&k): i64, 0i64);
	return r >= 0i64;
};

// rt — runtime primitives exposed to ww programs.
// Mirrors Hare's rt:: module placement (ref/hare/rt/).

package rt;

// malloc — mmap-backed page allocator. Untyped: `malloc(n)` returns a
// `*void`; callers cast to the target type. Diverges from Hare: Hare
// exposes `alloc` / `free` as typed language builtins that the
// compiler lowers to rt::malloc/rt::free; ww has no such builtins,
// so the rt-symbol surface is exposed directly. Stdlib callers that
// need a typed allocation pattern wrap this with a cast plus a stored
// capacity (see [[strings.dup]], [[memio.dynamic]]).
//
// OOM: rt_malloc is a bare mmap(MAP_ANON|MAP_PRIVATE) wrapper with no
// error path. The raw Linux mmap syscall returns a negative errno cast
// to `*void` on failure (e.g. `(void*)-12` for ENOMEM); the
// `MAP_FAILED` (`(void*)-1`) value is a libc-wrapper convention that
// rt_malloc doesn't apply. Neither `== nil` nor `== (void*)-1` catches
// it; any deref of such a return faults. Today the stdlib does not
// check; OOM faults on first dereference. A typed fallible variant is
// a future task (task #39). ref/hare/rt/malloc.ha:27.
@symbol("rt_malloc") export fn malloc(n: u64) *void;

// types — integer limits. Mirrors Hare's types::limits (I8_MAX, …)
// platform-fixed for amd64. Numeric helpers live in lib/math, matching
// Hare's split between types::limits and math::.

package types;

def I8_MAX:  i8  = 127;
def I16_MAX: i16 = 32767;
def I32_MAX: i32 = 2147483647;
def I64_MAX: i64 = 9223372036854775807;

def I8_MIN:  i8  = -128;
def I16_MIN: i16 = -32768;
def I32_MIN: i32 = -2147483648;
def I64_MIN: i64 = -9223372036854775808;

def U8_MAX:  u8  = 255;
def U16_MAX: u16 = 65535;
def U32_MAX: u32 = 4294967295;
def U64_MAX: u64 = 18446744073709551615;

def U8_MIN:  u8  = 0;
def U16_MIN: u16 = 0;
def U32_MIN: u32 = 0;
def U64_MIN: u64 = 0;

// int/uint are machine-word (Go-style, type.c:58); limits derived from
// size(int) per #114 + user ruling; cf Go math.MaxInt; diverges from
// Hare's per-arch literal (arch+x86_64.ha) because ww's int is 64-bit.
def INT_MAX:  int  = (1 << (size(int)*8 - 1)) - 1;
def INT_MIN:  int  = -1 << (size(int)*8 - 1);
def UINT_MIN: uint = 0;
def UINT_MAX: uint = ~(0: uint);

// size is 8B on amd64; no cast needed (size ∈ unsigned class per #113).
def SIZE_MIN: size = U64_MIN;
def SIZE_MAX: size = U64_MAX;

// uintptr not in the unsigned class, so the cast is required (Hare's form).
def UINTPTR_MIN: uintptr = U64_MIN: uintptr;
def UINTPTR_MAX: uintptr = U64_MAX: uintptr;

def RUNE_MIN: rune = '\0';

// bytes — slice operations over []u8. Mirrors Hare's bytes module
// (ref/hare/bytes/) for the in-tree subset: search/equality/prefix
// helpers used by lib/encoding, lib/bufio, lib/memio.
//
// Documented divergences from Hare:
//   - index_slice / rindex_slice use naive O(n·m); Hare specialises
//     2/3/4-byte needles and falls back to two_way (Crochemore-Perrin)
//     for longer (ref/hare/bytes/index.ha:61, ref/hare/bytes/two_way.ha).
//     Correctness equivalent.
//   - peek_token dispatches index/rindex by branching on `reverse`
//     rather than a function-pointer `ifunc` (ref/hare/bytes/tokenize.ha:97).
//     ww has no fn pointers in scope yet — same pattern as lib/strings
//     `move`. Outwardly identical.
//   - tokenize / rtokenize zero the `delim` field on the constructed
//     tokenizer when `in` is empty, rather than mutating the variadic
//     param before the struct write (ref/hare/bytes/tokenize.ha:26-28).
//     Semantically identical; the variadic param is borrowed and
//     captured-by-value into the struct, so mutating either side
//     yields the same observable state.

package bytes;

import os;
import types;

// done — iteration sentinel returned by next_token / peek_token at
// end-of-input. ref/hare/bytes/tokenize.ha uses the built-in `done`
// token; ww spells it per-package the same way lib/encoding/utf8 does
// (utf8.ww:36). Plain `void` (not `!void`): continuation signal.
export type done = void;

// tokenizer — cursor over an input slice. Layout mirrors
// ref/hare/bytes/tokenize.ha:6-10. `p` is the cached peek-position;
// I64_MAX (forward) / I64_MIN (reverse) are the unprimed sentinels.
// p < 0 also identifies a reverse-direction iterator.
export type tokenizer = struct {
	in:    []u8,
	delim: []u8,
	p:     i64,
};

// equal — true iff `a` and `b` have the same length and contents.
// ref/hare/bytes/equal.ha:9.
export fn equal(a: []u8, b: []u8) bool = {
	if (a.len != b.len) { return false; };
	let i: i32 = 0;
	for (i < a.len) {
		if (a[i] != b[i]) { return false; };
		i += 1;
	};
	return true;
};

// index — first offset of `needle` in `s`. u8 needle scans for the
// byte; []u8 needle scans for the substring. void if absent.
// ref/hare/bytes/index.ha:6.
export fn index(s: []u8, needle: (u8 | []u8)) (i32 | void) = {
	match (needle) {
	case let c: u8 => {
		let i: i32 = 0;
		for (i < s.len) {
			if (s[i] == c) { return i; };
			i += 1;
		};
		return;
	};
	case let sub: []u8 => {
		if (sub.len == 0) { return 0; };
		if (sub.len > s.len) { return; };
		let last: i32 = s.len - sub.len;
		let i: i32 = 0;
		for (i <= last) {
			let j: i32 = 0;
			let ok: bool = true;
			for (j < sub.len) {
				if (s[i + j] != sub[j]) { ok = false; j = sub.len; }
				else { j += 1; };
			};
			if (ok) { return i; };
			i += 1;
		};
		return;
	};
	};
	return;
};

// rindex — last offset of `needle` in `s`. Empty []u8 needle returns
// s.len (ref/hare/bytes/index.ha:103 — Hare's loop yields r-0 at i=0).
// ref/hare/bytes/index.ha:86.
export fn rindex(s: []u8, needle: (u8 | []u8)) (i32 | void) = {
	match (needle) {
	case let c: u8 => {
		let i: i32 = s.len - 1;
		for (i >= 0) {
			if (s[i] == c) { return i; };
			i -= 1;
		};
		return;
	};
	case let sub: []u8 => {
		if (sub.len == 0) { return s.len; };
		if (sub.len > s.len) { return; };
		let i: i32 = s.len - sub.len;
		for (i >= 0) {
			let j: i32 = 0;
			let ok: bool = true;
			for (j < sub.len) {
				if (s[i + j] != sub[j]) { ok = false; j = sub.len; }
				else { j += 1; };
			};
			if (ok) { return i; };
			i -= 1;
		};
		return;
	};
	};
	return;
};

// contains — true iff any of `needles` (byte or sub-slice) appears in `s`.
// ref/hare/bytes/contains.ha:6.
export fn contains(s: []u8, needles: (u8 | []u8)...) bool = {
	let i: i32 = 0;
	for (i < needles.len) {
		match (needles[i]) {
		case let b: u8   => {
			match (index(s, b)) {
			case let bo: i32 => return true;
			case void        => void;
			};
		};
		case let n: []u8 => {
			match (index(s, n)) {
			case let bo: i32 => return true;
			case void        => void;
			};
		};
		};
		i += 1;
	};
	return false;
};

// ltrim — borrowed view of `in` with leading bytes in `trim` stripped.
// `trim` must be non-empty. ref/hare/bytes/trim.ha:7.
export fn ltrim(in: []u8, trim: u8...) []u8 = {
	assert(trim.len > 0, "bytes.ltrim called with empty trim set");
	let i: i32 = 0;
	for (i < in.len && contains(trim, in[i])) { i += 1; };
	let r: []u8;
	r.ptr = in.ptr + (i: u64);
	r.len = in.len - i;
	r.cap = r.len;
	return r;
};

// rtrim — borrowed view of `in` with trailing bytes in `trim` stripped.
// `trim` must be non-empty. ref/hare/bytes/trim.ha:17. Hare's loop uses
// `size` underflow at i==0 to terminate; ww indices are signed i32, so
// the equivalent termination is spelled `i >= 0` explicitly.
export fn rtrim(in: []u8, trim: u8...) []u8 = {
	assert(trim.len > 0, "bytes.rtrim called with empty trim set");
	let i: i32 = in.len - 1;
	for (i >= 0 && contains(trim, in[i])) { i -= 1; };
	let r: []u8;
	r.ptr = in.ptr;
	r.len = i + 1;
	r.cap = r.len;
	return r;
};

// trim — borrowed view of `in` with both ends in `trim` stripped.
// ref/hare/bytes/trim.ha:27.
export fn trim(in: []u8, trim: u8...) []u8 = {
	return ltrim(rtrim(in, trim...), trim...);
};

// hasprefix — true iff `s` starts with `pre`.
// ref/hare/bytes/contains.ha:21.
export fn hasprefix(s: []u8, pre: []u8) bool = {
	if (pre.len > s.len) { return false; };
	let i: i32 = 0;
	for (i < pre.len) {
		if (s[i] != pre[i]) { return false; };
		i += 1;
	};
	return true;
};

// hassuffix — true iff `s` ends with `suf`.
// ref/hare/bytes/contains.ha:35.
export fn hassuffix(s: []u8, suf: []u8) bool = {
	if (suf.len > s.len) { return false; };
	let off: i32 = s.len - suf.len;
	let i: i32 = 0;
	for (i < suf.len) {
		if (s[off + i] != suf[i]) { return false; };
		i += 1;
	};
	return true;
};

// reverse — in-place reverse of `s`. ref/hare/bytes/reverse.ha:5.
export fn reverse(s: []u8) void = {
	let i: i32 = 0;
	let j: i32 = s.len - 1;
	for (i < j) {
		let t: u8 = s[i];
		s[i] = s[j];
		s[j] = t;
		i += 1;
		j -= 1;
	};
};

// zero — set every byte of `s` to 0. ref/hare/bytes/zero.ha:5.
export fn zero(s: []u8) void = {
	let i: i32 = 0;
	for (i < s.len) {
		s[i] = 0u8;
		i += 1;
	};
};

// tokenize — iterator yielding tokens from `in` separated by any byte
// in `delim`. Leading / trailing / adjacent delims yield empty tokens.
// `delim` is borrowed; caller keeps it valid for the tokenizer's
// lifetime. ref/hare/bytes/tokenize.ha:22.
export fn tokenize(in: []u8, delim: u8...) tokenizer = {
	assert(delim.len > 0, "bytes.tokenize called with empty slice");
	assert((in.len: i64) < types.I64_MAX,
		"bytes.tokenize: input length exceeds I64_MAX");
	let t: tokenizer;
	t.in = in;
	t.delim = delim;
	if (in.len == 0) {
		t.delim.len = 0;
		t.delim.cap = 0;
	};
	t.p = types.I64_MAX;
	return t;
};

// rtokenize — reverse-direction tokenize. First next_token yields the
// last token, last next_token yields the first. ref/hare/bytes/tokenize.ha:40.
export fn rtokenize(in: []u8, delim: u8...) tokenizer = {
	assert(delim.len > 0, "bytes.rtokenize called with empty slice");
	assert((in.len: i64) < types.I64_MAX,
		"bytes.rtokenize: input length exceeds I64_MAX");
	let t: tokenizer;
	t.in = in;
	t.delim = delim;
	if (in.len == 0) {
		t.delim.len = 0;
		t.delim.cap = 0;
	};
	t.p = types.I64_MIN;
	return t;
};

// peek_token — next token without advancing the cursor. Returns done
// once `s.delim` has been zeroed by a prior past-end next_token.
// ref/hare/bytes/tokenize.ha:91.
export fn peek_token(s: *tokenizer) ([]u8 | done) = {
	if (s.delim.len == 0) {
		let d: done; return d;
	};

	let reverse: bool = s.p < 0i64;
	let known: bool = false;
	if (reverse) {
		if (s.p != types.I64_MIN) { known = true; };
	} else {
		if (s.p != types.I64_MAX) { known = true; };
	};
	if (!known) {
		let i: i64 = types.I64_MAX;
		if (reverse) { i = types.I64_MIN; };
		let dlen: i64 = 0i64;
		let slen: i64 = s.in.len: i64;

		let k: i32 = 0;
		for (k < s.delim.len) {
			let d: u8 = s.delim[k];
			let ix_found: bool = false;
			let ix_val: i32 = 0;
			if (reverse) {
				match (rindex(s.in, d)) {
				case let v: i32 => { ix_found = true; ix_val = v; };
				case void       => void;
				};
			} else {
				match (index(s.in, d)) {
				case let v: i32 => { ix_found = true; ix_val = v; };
				case void       => void;
				};
			};
			if (ix_found) {
				if (!reverse) {
					if ((ix_val: i64) < i) { i = ix_val: i64; dlen = 1i64; };
				} else {
					if ((ix_val: i64) > i) { i = ix_val: i64; dlen = 1i64; };
				};
			} else {
				if (!reverse) {
					if (slen < i) { i = slen; };
				} else {
					if (0i64 > i) { i = 0i64; };
				};
			};
			k += 1;
		};

		if (reverse) {
			if (i == slen) {
				s.p = -(slen + 1i64);
			} else {
				s.p = i + dlen - slen - 1i64;
			};
		} else {
			s.p = i;
		};
	};

	let r: []u8;
	if (reverse) {
		let start: i32 = (s.in.len: i64 + s.p + 1i64): i32;
		r.ptr = s.in.ptr + (start: u64);
		r.len = s.in.len - start;
		r.cap = r.len;
	} else {
		let end: i32 = s.p: i32;
		r.ptr = s.in.ptr;
		r.len = end;
		r.cap = end;
	};
	return r;
};

// next_token — current token, then advance past it and the delim.
// Once the input is exhausted, returns done and zeros `s.delim` so
// subsequent peeks short-circuit. ref/hare/bytes/tokenize.ha:59.
export fn next_token(s: *tokenizer) ([]u8 | done) = {
	let b: []u8;
	match (peek_token(s)) {
	case let v: []u8 => { b = v; };
	case done        => { let d: done; return d; };
	};

	let slen: i64 = s.in.len: i64;
	let reverse: bool = s.p < 0i64;
	if (reverse) {
		if (slen + s.p + 1i64 == 0i64) {
			s.delim.len = 0;
			s.delim.cap = 0;
			s.in.len = 0;
			s.in.cap = 0;
		} else {
			let end: i32 = (slen + s.p + 1i64 - 1i64): i32;
			s.in.len = end;
			s.in.cap = end;
		};
		s.p = types.I64_MIN;
	} else {
		if (s.p == slen) {
			s.delim.len = 0;
			s.delim.cap = 0;
			s.in.len = 0;
			s.in.cap = 0;
		} else {
			let adv: u64 = (s.p: u64) + 1u64;
			let adv_i32: i32 = (s.p: i32) + 1;
			s.in.ptr = s.in.ptr + adv;
			s.in.len = s.in.len - adv_i32;
			s.in.cap = s.in.cap - adv_i32;
		};
		s.p = types.I64_MAX;
	};
	return b;
};

// remaining_tokens — the unconsumed portion of `s.in`. Read-only view.
// ref/hare/bytes/tokenize.ha:145.
export fn remaining_tokens(s: *tokenizer) []u8 = {
	return s.in;
};

// splitn — split `in` on any byte in `delim`, returning up to `n`
// tokens via forward iteration. The trailing slot (when more than
// `n - 1` tokens exist) holds the unconsumed remainder.
//
// The caller frees the returned slice via
// `os.free(r.ptr: *void, (r.cap: u64) * 24u64)`. Element bytes are
// borrowed from `in`.
//
// Hare's `([][]u8 | nomem)` collapses to `[][]u8` here: ww os.alloc
// has no recoverable failure path. Same precedent as
// shlex.split / getopt.tryparse.
//
// ref/hare/bytes/tokenize.ha:156.
export fn splitn(in: []u8, delim: []u8, n: i32) [][]u8 = {
	assert(delim.len > 0,
		"bytes.splitn must not be called with an empty delimiter");
	let toks: [][]u8;
	toks.ptr = nil: *[]u8;
	toks.len = 0;
	toks.cap = 0;
	let tok: tokenizer = tokenize(in, delim...);
	let i: i32 = 0;
	for (i < n - 1) {
		match (next_token(&tok)) {
		case let s: []u8 => { append(toks, s); };
		case done        => { return toks; };
		};
		i += 1;
	};
	match (peek_token(&tok)) {
	case done         => void;
	case let pk: []u8 => {
		let r: []u8 = remaining_tokens(&tok);
		append(toks, r);
	};
	};
	return toks;
};

// rsplitn — reverse-direction counterpart to [[splitn]]: tokens are
// collected from the end of `in`. The trailing slot holds the
// unconsumed prefix (everything before the n-th-from-last delim hit).
//
// When the input has fewer than n tokens, the `done` short-circuit
// returns toks UN-reversed (in last-token-first order). Mirrors Hare
// at ref/hare/bytes/tokenize.ha:196-199 where the in-place reverse
// step is gated behind the n-1 loop running to completion. Only the
// "loop ran to completion AND peek saw a remainder" path applies the
// reverse; both early-exit paths skip it.
//
// ref/hare/bytes/tokenize.ha:186.
export fn rsplitn(in: []u8, delim: []u8, n: i32) [][]u8 = {
	assert(delim.len > 0,
		"bytes.rsplitn called with empty delimiter");
	let toks: [][]u8;
	toks.ptr = nil: *[]u8;
	toks.len = 0;
	toks.cap = 0;
	let tok: tokenizer = rtokenize(in, delim...);
	let i: i32 = 0;
	for (i < n - 1) {
		match (next_token(&tok)) {
		case let s: []u8 => { append(toks, s); };
		case done        => { return toks; };
		};
		i += 1;
	};
	match (peek_token(&tok)) {
	case done         => void;
	case let pk: []u8 => {
		let r: []u8 = remaining_tokens(&tok);
		append(toks, r);
	};
	};

	// In-place reverse so callers see argv-order, matching Hare
	// (ref/hare/bytes/tokenize.ha:207). Element copy is field-wise
	// through `*[]u8` because `toks[i] = toks[j]` (full 24B slice
	// store) lands in the multi-word-store gap noted at
	// cmd/w6c/cgen.c:6515-6523.
	let a: i32 = 0;
	let b: i32 = toks.len - 1;
	for (a < b) {
		let pa: *[]u8 = &toks.ptr[a];
		let pb: *[]u8 = &toks.ptr[b];
		let tp: *u8 = pa.ptr;
		let tl: i32 = pa.len;
		let tc: i32 = pa.cap;
		pa.ptr = pb.ptr;
		pa.len = pb.len;
		pa.cap = pb.cap;
		pb.ptr = tp;
		pb.len = tl;
		pb.cap = tc;
		a += 1;
		b -= 1;
	};
	return toks;
};

// split — full split of `in` on `delim` (no token cap). Mirrors
// `splitn(in, delim, types::SIZE_MAX)`. ww uses `types.I32_MAX`
// because the index type is i32 (lib/CLAUDE.md).
//
// ref/hare/bytes/tokenize.ha:225.
export fn split(in: []u8, delim: []u8) [][]u8 = {
	return splitn(in, delim, types.I32_MAX);
};

// cut — split `in` along the first instance of `delim`, returning the
// portion before and the portion after the delimiter as a borrowed
// tuple. When `delim` is absent, the whole input is the first half and
// the second is empty. ref/hare/bytes/tokenize.ha:392.
//
// Delim is spelled (u8 | []u8) to match index/rindex (bytes.ww:57/91);
// the tagged union is an unordered set, so this is the same type as
// Hare's ([]u8 | u8), not a divergence.
export fn cut(in: []u8, delim: (u8 | []u8)) ([]u8, []u8) = {
	let ln: i32 = match (delim) {
	case let c: u8     => yield 1i32;
	case let sub: []u8 => {
		assert(sub.len > 0,
			"bytes.cut called with empty delimiter");
		yield sub.len;
	};
	};
	match (index(in, delim)) {
	case let i: i32 => {
		let lo: i32 = i + ln;
		return (in[0:i], in[lo:in.len]);
	};
	case void => {
		let empty: []u8;
		empty.ptr = nil; empty.len = 0; empty.cap = 0;
		return (in, empty);
	};
	};
};

// rcut — like [[cut]] but splits along the last instance of `delim`.
// ref/hare/bytes/tokenize.ha:413.
export fn rcut(in: []u8, delim: (u8 | []u8)) ([]u8, []u8) = {
	let ln: i32 = match (delim) {
	case let c: u8     => yield 1i32;
	case let sub: []u8 => {
		assert(sub.len > 0,
			"bytes.rcut called with empty delimiter");
		yield sub.len;
	};
	};
	match (rindex(in, delim)) {
	case let i: i32 => {
		let lo: i32 = i + ln;
		return (in[0:i], in[lo:in.len]);
	};
	case void => {
		let empty: []u8;
		empty.ptr = nil; empty.len = 0; empty.cap = 0;
		return (in, empty);
	};
	};
};

// encoding/utf8 — UTF-8 encode/decode. Hare port; see
// ref/hare/encoding/utf8/{types,rune,encode,decode,decodetable}.ha.
//
// The decoder is Hoehrmann's branchless DFA, originally published
// at <https://bjoern.hoehrmann.de/utf-8/decoder/dfa/>. Hare's
// ref/hare/encoding/utf8/decodetable.ha:4 restructures Hoehrmann's
// flat table to 2D `[8][256]i8`; we flatten back to 1D `[2048]i8`
// because ww cgen does not yet ship 2D arrays (task #20).
//
// Surface deviation from ref/hare/encoding/utf8:
//
//   - `encoderune` takes a caller-supplied `out: []u8` and returns
//     the byte count. Hare returns a slice into a `static let buf`;
//     the caller-buffer form skips the static-buffer/slice-return pair.
//
// Deferred (no in-tree caller, follow-up tasks): `appendrune`,
// `strencode`, `strdecode`. Hare's string-iteration surface
// (`strings::iterator`/`strings::next` — ref/hare/strings/iter.ha)
// lives under lib/strings, not here.

// ref/hare/encoding/utf8/types.ha:6 — incomplete trailing sequence.
// Plain `void` (not `!void`): a truncated tail is a control-flow
// signal, not an error caller can ignore.
package utf8;

export type more = void;

// ref/hare/encoding/utf8/types.ha:9 — invalid UTF-8 sequence.
export type invalid = !void;

// ref/hare/encoding/utf8/types.ha:12 — fixed message; `invalid` carries
// no payload, so the rendering is constant.
export fn strerror(err: invalid) str = {
	return "Invalid UTF-8";
};

// `done` is not a built-in singleton in ww (Hare ships it as part of
// the type system). Plain `void` (not `!void`): end-of-input is a
// continuation signal, not an error. lib/io spells its EOF the same
// way (lib/io/io.ww:8-11).
export type done = void;

// ref/hare/encoding/utf8/decodetable.ha:4 — Hoehrmann's UTF-8 DFA,
// flat 1D `[2048]i8`. Layout: dfa[state*256 + byte] gives the next
// state (>0), the accept transition (0 — emit rune), or invalid (-1).
// Values match ref/hare/encoding/utf8/decodetable.ha verbatim.
let dfa: [2048]i8 = [
	// state 0 — initial byte: ASCII accepts (0), continuation/illegal
	// byte rejects (-1), legal multibyte start emits a state.
	0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8,
	0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8,
	0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8,
	0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8,
	0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8,
	0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8,
	0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8,
	0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8,
	1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8,
	3i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 4i8, 2i8, 2i8,
	5i8, 6i8, 6i8, 6i8, 7i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,

	// state 1 — expecting one continuation byte (0x80..0xBF).
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8,
	0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8,
	0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8,
	0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8, 0i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,

	// state 2 — expecting one continuation byte (full 0x80..0xBF range).
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8,
	1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8,
	1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8,
	1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,

	// state 3 — first byte was 0xE0; continuation byte must be 0xA0..0xBF
	// (rejects overlong 3-byte encodings).
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8,
	1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,

	// state 4 — first byte was 0xED; continuation byte must be 0x80..0x9F
	// (rejects UTF-16 surrogate codepoints U+D800..U+DFFF).
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8,
	1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8, 1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,

	// state 5 — first byte was 0xF0; continuation byte must be 0x90..0xBF
	// (rejects overlong 4-byte encodings).
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8,
	2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8,
	2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,

	// state 6 — middle continuation byte of a 4-byte sequence (0x80..0xBF).
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8,
	2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8,
	2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8,
	2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,

	// state 7 — first byte was 0xF4; continuation byte must be 0x80..0x8F
	// (rejects codepoints above U+10FFFF).
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8, 2i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
	-1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8, -1i8,
];

// ref/hare/encoding/utf8/decode.ha:17 — payload-bit masks. Hare's
// [2][8]u8 flattened to 1D [16]u8; row 0 (offsets 0..7) is the
// continuation-byte mask (always 0x3F), row 1 (offsets 8..15) is the
// initial-byte payload mask indexed by the transition class.
let masks: [16]u8 = [
	0x3fu8, 0x3fu8, 0x3fu8, 0x3fu8, 0x3fu8, 0x3fu8, 0x3fu8, 0x3fu8,
	0x7fu8, 0x1fu8, 0x0fu8, 0x0fu8, 0x0fu8, 0x07u8, 0x07u8, 0x07u8,
];

// ref/hare/encoding/utf8/decode.ha:6 — incremental decoder state.
export type decoder = struct {
	offs: i32,
	src:  []u8,
};

// ref/hare/encoding/utf8/decode.ha:12.
export fn decode(src: []u8) decoder = {
	let d: decoder;
	d.src = src;
	d.offs = 0;
	return d;
};

// ref/hare/encoding/utf8/decode.ha:27. Returns the next rune from a
// decoder, `done` at end-of-input, `more` on truncated trailing
// sequence, `invalid` on malformed input (overlong, surrogate,
// out-of-range, bad continuation).
//
// Algorithm is verbatim Hoehrmann (see file header). One structural
// rewrite: Hare encodes the "initial vs continuation byte" decision
// as the branchless `(state - 1): uint >> 31`, which assumes a 32-bit
// uint. ww's uint is 64-bit (cmd/wcc/type.c:58), so the shift answer
// would be 0x1_ffff_ffff rather than 1. We spell the same predicate
// with an explicit conditional.
export fn next(d: *decoder) (rune | done | more | invalid) = {
	if (d.offs == d.src.len) {
		let dn: done; return dn;
	};
	let nx: i32 = 0;
	let state: i32 = 0;
	let r: u32 = 0u32;
	for (d.offs < d.src.len) {
		let b: u8 = d.src[d.offs];
		let bi: i32 = b: i32;
		let row: i32 = state * 256 + bi;
		let cell: i8 = dfa[row];
		nx = cell: i32;
		let mi: i32 = 0;
		if (state == 0) { mi = 1; };
		let m: u8 = masks[mi * 8 + (nx & 7)];
		r = (r << 6u32) | ((b & m): u32);
		if (nx <= 0) {
			d.offs += 1;
			if (nx == 0) { return r: rune; };
			let e: invalid; return e;
		};
		state = nx;
		d.offs += 1;
	};
	let mr: more; return mr;
};

// ref/hare/encoding/utf8/decode.ha:207. Strict whole-input check.
// The hot path: tight DFA loop, no rune assembly. Bails the moment
// the table returns -1 so malformed inputs don't pay for the rest
// of the buffer.
export fn validate(src: []u8) (void | invalid) = {
	let state: i32 = 0;
	let i: i32 = 0;
	for (i < src.len) {
		if (state < 0) { break; };
		let bi: i32 = src[i]: i32;
		let cell: i8 = dfa[state * 256 + bi];
		state = cell: i32;
		i += 1;
	};
	if (state == 0) { return; };
	let e: invalid; return e;
};

// ref/hare/encoding/utf8/rune.ha:5. Encoded byte length of `r` as
// UTF-8. Callers in ww use this to size the buffer they hand to
// [[encoderune]]; values >0x10FFFF or negative are not legal Unicode
// codepoints and Hare aborts on them in `encoderune` itself, so we
// keep `runesz` infallible (matches Hare).
export fn runesz(r: rune) i32 = {
	let ch: u32 = r: u32;
	if (ch < 128u32)    { return 1; };
	if (ch < 2048u32)   { return 2; };
	if (ch < 65536u32)  { return 3; };
	return 4;
};

// ref/hare/encoding/utf8/rune.ha:15. Expected byte length of the
// codepoint that starts with `c`, or `invalid` if `c` cannot start
// a legal UTF-8 sequence. Constants written in decimal because ww
// doesn't accept Hare's `0b1000_0000` binary syntax: 0x80=128,
// 0xC2=194, 0xE0=224, 0xF0=240, 0xF8=248.
export fn utf8sz(c: u8) (i32 | invalid) = {
	if (c < 128u8) { return 1; };
	if (c < 194u8) { let e: invalid; return e; };
	if (c >= 248u8) { let e: invalid; return e; };
	if (c < 224u8) { return 2; };
	if (c < 240u8) { return 3; };
	return 4;
};

// ref/hare/encoding/utf8/encode.ha:7. Encode `r` into `out` (caller-
// supplied; must hold at least [[runesz]](r) bytes) and return the
// byte count. ABORT if `r` is a UTF-16 surrogate or above U+10FFFF —
// same precondition Hare asserts at ref/hare/encoding/utf8/encode.ha:9.
//
// Surface deviation: Hare returns `[]u8` (slice into a static buf).
// ww uses the caller-buffer form; caller can reuse a [4]u8 stack
// scratch across encodes.
export fn encoderune(out: []u8, r: rune) i32 = {
	let ch: u32 = r: u32;
	if (ch >= 0xD800u32) {
		if (ch <= 0xDFFFu32) {
			abort("utf8.encoderune: surrogate codepoint");
		};
	};
	if (ch > 0x10FFFFu32) {
		abort("utf8.encoderune: codepoint > U+10FFFF");
	};

	let n: i32 = 0;
	let first: u8 = 0u8;
	if (ch < 0x80u32) {
		first = 0u8; n = 1;
	} else if (ch < 0x800u32) {
		first = 0xC0u8; n = 2;
	} else if (ch < 0x10000u32) {
		first = 0xE0u8; n = 3;
	} else {
		first = 0xF0u8; n = 4;
	};

	let v: u32 = ch;
	let i: i32 = n - 1;
	for (i > 0) {
		out[i] = ((v: u8) & 0x3Fu8) | 0x80u8;
		v = v >> 6u32;
		i -= 1;
	};
	out[0] = (v: u8) | first;
	return n;
};

// ref/hare/encoding/utf8/decode.ha:52. Walks back from `d.offs` to a
// byte that could start a codepoint (state-0 dfa cell != -1), re-decodes
// forward from there, and confirms the forward decode lands back at the
// original offset. Returns `done` at start-of-input; `invalid` if no
// initial byte appears within 4 steps (no legal UTF-8 codepoint exceeds
// 4 bytes), if the forward decode returns `more`/`invalid`, or if it
// lands at a different offset than expected. Returns `more` when the
// walk reaches byte 0 without finding any initial byte.
//
// Hare's `for (d.offs < len(d.src); d.offs -= 1)` relies on size_t
// wrap-around to exit when offs underflows past 0; ww's offs is i32,
// so we spell the same exit as `d.offs >= 0`. Hare's `defer d.offs = t`
// is inlined in each match arm — ww has no defer.
export fn prev(d: *decoder) (rune | done | more | invalid) = {
	if (d.offs == 0) {
		let dn: done; return dn;
	};
	let n: i32 = d.offs;
	d.offs -= 1;
	for (d.offs >= 0) {
		let b: u8 = d.src[d.offs];
		let bi: i32 = b: i32;
		let cell: i8 = dfa[bi];
		if (cell: i32 != -1) {
			let t: i32 = d.offs;
			match (next(d)) {
			case let r: rune => {
				let landed: i32 = d.offs;
				d.offs = t;
				if (landed != n) {
					let e: invalid; return e;
				};
				return r;
			};
			case let dn: done => {
				d.offs = t;
				let e: invalid; return e;
			};
			case let m: more => {
				d.offs = t;
				let e: invalid; return e;
			};
			case let e: invalid => {
				d.offs = t;
				let e2: invalid; return e2;
			};
			};
		};
		if (n - d.offs == 4) {
			let e: invalid; return e;
		};
		d.offs -= 1;
	};
	let mr: more; return mr;
};

// ref/hare/encoding/utf8/decode.ha:74. Borrowed view of the bytes from
// the decoder's current position to the end of its source.
export fn remaining(d: *decoder) []u8 = {
	let r: []u8;
	r.ptr = d.src.ptr + (d.offs: u64);
	r.len = d.src.len - d.offs;
	r.cap = d.src.len - d.offs;
	return r;
};

// ref/hare/encoding/utf8/decode.ha:80. Borrowed view of the bytes
// between two decoders' positions. Precondition (Hare asserts both):
// the decoders share the same source, and `begin.offs <= end.offs`.
export fn slice(begin: *decoder, end: *decoder) []u8 = {
	if (begin.src.ptr != end.src.ptr) {
		abort("utf8.slice: decoders from different sources");
	};
	if (begin.offs > end.offs) {
		abort("utf8.slice: begin past end");
	};
	let r: []u8;
	r.ptr = begin.src.ptr + (begin.offs: u64);
	r.len = end.offs - begin.offs;
	r.cap = end.offs - begin.offs;
	return r;
};

// ref/hare/encoding/utf8/decode.ha:203. Byte position of the decoder
// in its source.
export fn position(d: *decoder) i32 = {
	return d.offs;
};


// strings — operations over str ({ptr,len}). Hare port; see
// ref/hare/strings/.
//
// Documented divergences from Hare:
//
//   - `byteindex` / `rbyteindex` rune arms encode via
//     `utf8.encoderune`; the legacy impls scanned for `r: u8` (an
//     undocumented ASCII-only restriction that silently dropped
//     to the wrong byte for U+80..U+7FF and higher).
//   - `dup(s: str) str` — Hare returns `(str | nomem)`. ww's
//     `os.alloc` aborts on OOM (no `nomem` type), so we return plain
//     `str`. Empty input returns `{nil, 0}`; Hare returns the static
//     empty string — same observable result.
//   - `iterator` is flattened (`offs`, `src`, `reverse` fields).
//     Hare uses anonymous-embedded `utf8::decoder`
//     (ref/hare/strings/iter.ha:6-9); ww has no anonymous-embed
//     syntax, so `next`/`prev`/`slice` copy `offs`/`src` into a
//     local `utf8.decoder` for the call (and `next`/`prev` write
//     `offs` back).
//   - Hare's private `move()` helper dispatches on a `forward: bool`
//     using a function-pointer `let fun = if (forward) &utf8::next
//     else &utf8::prev`. ww has no fn-pointers in scope yet, so the
//     dispatch is a branch on `forward` selecting the call site.

package strings;

import bytes;
import encoding.utf8;
import os;
import rt;
import types;

// toutf8 — borrowed []u8 view of `s`. ref/hare/strings/utf8.ha:29.
// `cap` equals `len`; the slice does not own a separate allocation.
export fn toutf8(s: str) []u8 = {
	let r: []u8;
	r.ptr = s.ptr;
	r.len = s.len;
	r.cap = s.len;
	return r;
};

// frombytes — borrowed str view of `in`. Pure reinterpret per
// CLAUDE.md rule 9 carve-out; ref/hare/strings/utf8.ha:10.
export fn frombytes(in: []u8) str = {
	let r: str;
	r.ptr = in.ptr;
	r.len = in.len;
	return r;
};

// compare — three-way bytewise codepoint-order comparison. Return is
// a sign (neg/zero/pos), not an index, so it tracks Hare's `int`
// rather than the str-index i32 (#8). ref/hare/strings/compare.ha:12.
export fn compare(a: str, b: str) int = {
	let n: i32 = a.len;
	if (b.len < n) { n = b.len; };
	let i: i32 = 0;
	for (i < n) {
		if (a[i] != b[i]) { return (a[i]: int) - (b[i]: int); };
		i += 1;
	};
	return (a.len: int) - (b.len: int);
};

// dup — allocate a fresh copy of `s`. Caller releases with
// `os.free(r.ptr, r.len: u64)`. ref/hare/strings/dup.ha:7.
export fn dup(s: str) str = {
	let r: str;
	r.ptr = nil;
	r.len = 0;
	if (s.len == 0) { return r; };
	let buf: []u8 = alloc([], s.len: u64)!;
	let i: i32 = 0;
	for (i < s.len) { buf[i] = s[i]; i += 1; };
	buf.len = s.len;
	return frombytes(buf);
};

// dupall — fresh `[]str` whose elements are independent copies of
// `s`'s elements. Caller releases via [[freeall]].
// ref/hare/strings/dup.ha:26 (#6).
//
// Hare gates the per-element dup behind `?` and rolls back via
// `defer if (!ok) freeall(newsl)`. ww has no `defer if`; more
// importantly, ww's [[dup]] is still unchecked (returns plain `str`,
// aborts via os.alloc on OOM — see top-of-file divergence note),
// so the only nomem propagation point is the initial slice alloc.
// With no inner failure path, the rollback is structurally a no-op
// and is omitted; it returns once dup graduates to `(str | nomem)`
// (#46). The pre-allocated slice has `cap == s.len`, so append's
// rt_ensure call never reaches the grow branch.
//
// Empty input bypasses the alloc: rt_malloc(0) is an mmap of 0 bytes
// which returns -EINVAL, and the alloc-slice `?` shortcut routes
// that through nomem — Hare's heap allocator hands back a sentinel
// instead (#47). Return `{nil, 0, 0}` directly so callers get the
// Hare-observable shape (len==0, freeall is a no-op via cap==0).
export fn dupall(s: []str) ([]str | nomem) = {
	if (s.len == 0) {
		let r: []str;
		r.ptr = nil: *str;
		r.len = 0;
		r.cap = 0;
		return r;
	};
	let newsl: []str = alloc([], s.len)?;
	let i: i32 = 0;
	for (i < s.len) {
		append(newsl, dup(s[i]));
		i += 1;
	};
	return newsl;
};

// freeall — release each element + the slice header. The natural
// disposer for any `[]str` of dup'd elements (e.g. shlex.split).
// ref/hare/strings/dup.ha:38.
//
// Empty elements (`{nil, 0}` from a zero-length dup) are skipped:
// os.free on a nil pointer at len 0 tickles the rt_free guard. The
// slice header itself is freed at `cap * size(str)` — the literal
// would drift under #1's str-layout bump, so route through the
// typ.ww SSoT. A never-grown slice (cap == 0) skips the header free.
export fn freeall(s: []str) void = {
	let i: i32 = 0;
	for (i < s.len) {
		if (s[i].len > 0) {
			os.free(s[i].ptr: *void, s[i].len: u64);
		};
		i += 1;
	};
	if (s.cap > 0) {
		os.free(s.ptr: *void, (s.cap: u64) * size(str): u64);
	};
};

// concat — fresh allocation containing each element of `strs` in
// order. Caller releases with `os.free(r.ptr, r.len: u64)`.
// ref/hare/strings/concat.ha:5. Hare's `nomem` return is dropped:
// `os.alloc` aborts on OOM.
export fn concat(strs: str...) str = {
	let total: i32 = 0;
	let i: i32 = 0;
	for (i < strs.len) { total += strs[i].len; i += 1; };
	let r: str;
	r.ptr = nil;
	r.len = 0;
	if (total == 0) { return r; };
	let buf: []u8 = alloc([], total: u64)!;
	let off: i32 = 0;
	i = 0;
	for (i < strs.len) {
		let j: i32 = 0;
		for (j < strs[i].len) {
			buf[off + j] = strs[i][j];
			j += 1;
		};
		off += strs[i].len;
		i += 1;
	};
	buf.len = total;
	return frombytes(buf);
};

// join — fresh allocation with `delim` placed between each element of
// `strs`. Caller releases with `os.free(r.ptr, r.len: u64)`.
// ref/hare/strings/concat.ha:46. Hare's `nomem` return is dropped:
// `os.alloc` aborts on OOM.
export fn join(delim: str, strs: str...) str = {
	let total: i32 = 0;
	let i: i32 = 0;
	for (i < strs.len) {
		total += strs[i].len;
		if (i + 1 < strs.len) { total += delim.len; };
		i += 1;
	};
	let r: str;
	r.ptr = nil;
	r.len = 0;
	if (total == 0) { return r; };
	let buf: []u8 = alloc([], total: u64)!;
	let off: i32 = 0;
	i = 0;
	for (i < strs.len) {
		let j: i32 = 0;
		for (j < strs[i].len) {
			buf[off + j] = strs[i][j];
			j += 1;
		};
		off += strs[i].len;
		if (i + 1 < strs.len) {
			j = 0;
			for (j < delim.len) {
				buf[off + j] = delim[j];
				j += 1;
			};
			off += delim.len;
		};
		i += 1;
	};
	buf.len = total;
	return frombytes(buf);
};

// utf8bytelenbounded — walk `it` forward `end` runes and return the
// resulting byte offset. ref/hare/strings/sub.ha:10. Aborts on
// short input per Hare's contract for the rune-wise [[sub]].
fn utf8bytelenbounded(it: *iterator, end: i32) i32 = {
	let i: i32 = 0;
	for (i < end) {
		match (next(it)) {
		case let r: rune => void;
		case utf8.done   => abort("strings.sub: index exceeds string length");
		};
		i += 1;
	};
	return it.offs;
};

// sub — borrowed substring [start, end) where start/end are rune
// indices. ref/hare/strings/sub.ha:30. Hare's 2-arg `sub(s, start)`
// defaulting end=END is omitted: ww has no default-parameter syntax
// (filed as #37). Byte-indexed counterpart: [[bytesub]].
export fn sub(s: str, start: i32, end: i32) str = {
	assert(start <= end, "strings.sub: start is higher than end");
	let it: iterator = iter(s);
	let starti: i32 = utf8bytelenbounded(&it, start);
	let endi: i32 = utf8bytelenbounded(&it, end - start);
	let r: str;
	r.ptr = s.ptr + (starti: u64);
	r.len = endi - starti;
	return r;
};

// bytesub — borrowed substring [start, end) where start/end are byte
// offsets. ref/hare/strings/sub.ha:59 (#7). Returns `utf8.invalid` if
// either endpoint lands on a continuation byte (would split a
// codepoint); the equivalent Hare predicate is `s[i] & 0xc0 == 0x80`
// at ref/hare/strings/sub.ha:72-73.
export fn bytesub(s: str, start: i32, end: i32) (str | utf8.invalid) = {
	assert(start <= end, "strings.bytesub: start is higher than end");
	assert(end <= s.len, "strings.bytesub: end exceeds string length");
	if (start < s.len && (s[start] & 0xC0u8) == 0x80u8) {
		let e: utf8.invalid; return e;
	};
	if (end < s.len && (s[end] & 0xC0u8) == 0x80u8) {
		let e: utf8.invalid; return e;
	};
	let r: str;
	r.ptr = s.ptr + (start: u64);
	r.len = end - start;
	return r;
};

// runebytes — encode `r` into caller's `scratch` (must hold 4 bytes)
// and return the borrowed slice trimmed to the encoded length. Hare
// inlines the same shape at ref/hare/strings/index.ha:132.
fn runebytes(scratch: []u8, r: rune) []u8 = {
	let n: i32 = utf8.encoderune(scratch, r);
	let s: []u8;
	s.ptr = scratch.ptr;
	s.len = n;
	s.cap = n;
	return s;
};

// hasprefix — true iff `in` begins with `prefix`.
// ref/hare/strings/suffix.ha:8.
export fn hasprefix(in: str, prefix: (str | rune)) bool = {
	let scratch: [4]u8;
	let p: []u8 = match (prefix) {
	case let s: str  => yield toutf8(s);
	case let r: rune => yield runebytes(scratch[0:4], r);
	};
	return bytes.hasprefix(toutf8(in), p);
};

// hassuffix — true iff `in` ends with `suff`.
// ref/hare/strings/suffix.ha:26.
export fn hassuffix(in: str, suff: (str | rune)) bool = {
	let scratch: [4]u8;
	let s: []u8 = match (suff) {
	case let v: str  => yield toutf8(v);
	case let r: rune => yield runebytes(scratch[0:4], r);
	};
	return bytes.hassuffix(toutf8(in), s);
};

// byteindex — byte-wise offset of `needle` in `haystack`, or void if
// absent. ref/hare/strings/index.ha:127. Rune arm encodes via
// utf8.encoderune (Hare passes the encoded slice straight to
// bytes::index).
export fn byteindex(haystack: str, needle: (str | rune)) (i32 | void) = {
	let scratch: [4]u8;
	let n: []u8 = match (needle) {
	case let s: str  => yield toutf8(s);
	case let r: rune => yield runebytes(scratch[0:4], r);
	};
	return bytes.index(toutf8(haystack), n);
};

// rbyteindex — byte-wise offset of the last `needle` in `haystack`.
// ref/hare/strings/index.ha:138.
export fn rbyteindex(haystack: str, needle: (str | rune)) (i32 | void) = {
	let scratch: [4]u8;
	let n: []u8 = match (needle) {
	case let s: str  => yield toutf8(s);
	case let r: rune => yield runebytes(scratch[0:4], r);
	};
	return bytes.rindex(toutf8(haystack), n);
};

// indexstring — str-arm of [[index]]. Dual-rune-iterator walk: at each
// candidate rune index `i`, compare `haystack` from that position
// against `needle` rune-by-rune until needle is exhausted (match) or
// a mismatch / haystack-exhaustion breaks the inner loop. Mirrors
// ref/hare/strings/index.ha:59 (#10). Hare copies `rest_iter = s_iter`
// directly via struct assignment; ww re-seats `rest_iter` field-wise
// because the let-init struct-copy form diverges between cstage and
// wwstage on this iterator type (993_ww_ww + 995_self_rebuild fail,
// filed as #41) and rule #10 (CLAUDE.md) forbids stage asymmetry.
fn indexstring(haystack: str, needle: str) (i32 | void) = {
	let s_iter: iterator = iter(haystack);
	let i: i32 = 0;
	for (true) {
		let rest_iter: iterator;
		rest_iter.src = s_iter.src;
		rest_iter.offs = s_iter.offs;
		rest_iter.reverse = s_iter.reverse;
		let needle_iter: iterator = iter(needle);
		let matched: bool = false;
		for (true) {
			let rest_done:   bool = false;
			let rest_r:      rune;
			match (next(&rest_iter)) {
			case let r: rune => rest_r = r;
			case utf8.done   => rest_done = true;
			};
			let needle_done: bool = false;
			let needle_r:    rune;
			match (next(&needle_iter)) {
			case let r: rune => needle_r = r;
			case utf8.done   => needle_done = true;
			};
			if (rest_done && !needle_done) { break; };
			if (needle_done) { matched = true; break; };
			if (rest_r != needle_r) { break; };
		};
		if (matched) { return i; };
		match (next(&s_iter)) {
		case let r: rune => i += 1;
		case utf8.done   => return;
		};
	};
	return;
};

// index — rune-wise offset of `needle`'s first occurrence in
// `haystack`, or void if absent. ref/hare/strings/index.ha:10. The
// str-arm delegates to [[indexstring]] (dual-iterator rune-by-rune
// walk per Hare's `index_string`, #10); the rune-arm mirrors Hare's
// `index_rune` (ref/hare/strings/index.ha:31).
export fn index(haystack: str, needle: (str | rune)) (i32 | void) = {
	match (needle) {
	case let s: str  => return indexstring(haystack, s);
	case let r: rune => {
		let it: iterator = iter(haystack);
		let i: i32 = 0;
		for (true) {
			match (next(&it)) {
			case let n: rune => {
				if (n == r) { return i; };
				i += 1;
			};
			case utf8.done   => return;
			};
		};
	};
	};
	return;
};

// rindex — rune-wise offset of `needle`'s last occurrence in
// `haystack`, or void if absent. ref/hare/strings/index.ha:22. The
// str-arm reuses `rbyteindex`; the rune-arm walks forward tracking
// the most recent matching rune index (Hare's `rindex_rune` with
// `riter` returns a byte-offset value for multibyte strings, which
// disagrees with the rune-wise docstring; we keep the docstring's
// contract).
export fn rindex(haystack: str, needle: (str | rune)) (i32 | void) = {
	match (needle) {
	case let s: str  => {
		match (rbyteindex(haystack, s)) {
		case void        => return;
		case let bo: i32 => {
			let it: iterator = iter(haystack);
			let i: i32 = 0;
			for (position(&it) < bo) {
				match (next(&it)) {
				case let r: rune => i += 1;
				case utf8.done   => break;
				};
			};
			return i;
		};
		};
	};
	case let r: rune => {
		let it: iterator = iter(haystack);
		let i: i32 = 0;
		let last: i32 = -1;
		for (true) {
			match (next(&it)) {
			case let n: rune => {
				if (n == r) { last = i; };
				i += 1;
			};
			case utf8.done   => break;
			};
		};
		if (last < 0) { return; };
		return last;
	};
	};
	return;
};

// contains — true iff any of `needles` occurs in `haystack`.
// ref/hare/strings/contains.ha:9.
export fn contains(haystack: str, needles: (str | rune)...) bool = {
	let i: i32 = 0;
	for (i < needles.len) {
		match (needles[i]) {
		case let s: str  => {
			match (byteindex(haystack, s)) {
			case let bo: i32 => return true;
			case void        => void;
			};
		};
		case let r: rune => {
			match (byteindex(haystack, r)) {
			case let bo: i32 => return true;
			case void        => void;
			};
		};
		};
		i += 1;
	};
	return false;
};

// trimprefix — `s` with `prefix` stripped from the front, or `s`
// unchanged if it doesn't start with `prefix`. Borrowed view.
// ref/hare/strings/trim.ha:60.
export fn trimprefix(input: str, prefix: str) str = {
	if (!hasprefix(input, prefix)) { return input; };
	let r: str;
	r.ptr = input.ptr + (prefix.len: u64);
	r.len = input.len - prefix.len;
	return r;
};

// trimsuffix — symmetric. ref/hare/strings/trim.ha:69.
export fn trimsuffix(input: str, suffix: str) str = {
	if (!hassuffix(input, suffix)) { return input; };
	let r: str;
	r.ptr = input.ptr;
	r.len = input.len - suffix.len;
	return r;
};

// whitespace — ASCII whitespace set used by the 0-arg ltrim/rtrim/trim
// branches (#9). ref/hare/strings/trim.ha:6.
let whitespace: [4]u8 = [0x20u8, 0x0Au8, 0x09u8, 0x0Du8];

// ltrim — strip leading runes that occur in `trim`. Borrowed view.
// 0-arg strips ASCII whitespace via [[bytes.ltrim]] (#9).
// ref/hare/strings/trim.ha:11. The spread expression is inlined
// because `let ws: []u8 = whitespace[0:4]` produces a slice whose
// ptr doesn't track the module-level array storage (filed as #40);
// `b.flush = flushdefault[0:1]` in lib/bufio is the same shape via
// the working field-assign path.
export fn ltrim(input: str, trim: rune...) str = {
	if (trim.len == 0) {
		return frombytes(bytes.ltrim(toutf8(input), whitespace[0:4]...));
	};
	let it: iterator = iter(input);
	for (true) {
		match (next(&it)) {
		case let r: rune => {
			let j: i32 = 0;
			let found: bool = false;
			for (j < trim.len) {
				if (r == trim[j]) { found = true; j = trim.len; }
				else { j += 1; };
			};
			if (!found) {
				match (prev(&it)) {
				case let r2: rune => void;
				case utf8.done    => void;
				};
				break;
			};
		};
		case utf8.done => break;
		};
	};
	return iterstr(&it);
};

// rtrim — strip trailing runes that occur in `trim`. Borrowed view.
// 0-arg strips ASCII whitespace via [[bytes.rtrim]] (#9). Spread is
// inlined to dodge #40 — see [[ltrim]].
// ref/hare/strings/trim.ha:32.
export fn rtrim(input: str, trim: rune...) str = {
	if (trim.len == 0) {
		return frombytes(bytes.rtrim(toutf8(input), whitespace[0:4]...));
	};
	let it: iterator = riter(input);
	for (true) {
		match (next(&it)) {
		case let r: rune => {
			let j: i32 = 0;
			let found: bool = false;
			for (j < trim.len) {
				if (r == trim[j]) { found = true; j = trim.len; }
				else { j += 1; };
			};
			if (!found) {
				match (prev(&it)) {
				case let r2: rune => void;
				case utf8.done    => void;
				};
				break;
			};
		};
		case utf8.done => break;
		};
	};
	return iterstr(&it);
};

// trim — strip from both ends. ref/hare/strings/trim.ha:54.
export fn trim(input: str, trim: rune...) str = {
	return ltrim(rtrim(input, trim...), trim...);
};

// iterator — UTF-8 rune cursor over a `str`. Layout flattens Hare's
// anonymous-embedded `utf8::decoder` (ref/hare/strings/iter.ha:6-9) to
// explicit fields. `reverse` selects walk direction: forward iterators
// (`iter`) advance through utf8.next; reverse iterators (`riter`) advance
// through utf8.prev. May be copied to save state.
export type iterator = struct {
	offs:    i32,
	src:     []u8,
	reverse: bool,
};

// iter — initialize a forward iterator at the start of `src`.
// ref/hare/strings/iter.ha:24.
export fn iter(src: str) iterator = {
	let r: iterator;
	r.src = toutf8(src);
	r.offs = 0;
	r.reverse = false;
	return r;
};

// riter — initialize a reverse iterator at the end of `src`. `next`
// on a reverse iterator walks back through the string.
// ref/hare/strings/iter.ha:32.
export fn riter(src: str) iterator = {
	let r: iterator;
	r.src = toutf8(src);
	r.offs = src.len;
	r.reverse = true;
	return r;
};

// move — private dispatch shared by next/prev. `forward` selects
// utf8.next vs utf8.prev. Aborts on more/invalid per Hare's
// ref/hare/strings/iter.ha:51-58 ("Invalid UTF-8 string (this should
// not happen)"). Hare picks the utf8 function via a fn-pointer; ww
// branches on `forward` at each call site instead.
fn move(forward: bool, it: *iterator) (rune | utf8.done) = {
	let d: utf8.decoder;
	d.src = it.src;
	d.offs = it.offs;
	if (forward) {
		match (utf8.next(&d)) {
		case let r: rune          => { it.offs = d.offs; return r; };
		case let dn: utf8.done    => return dn;
		case let m:  utf8.more    => abort("strings.move: invalid UTF-8");
		case let e:  utf8.invalid => abort("strings.move: invalid UTF-8");
		};
	} else {
		match (utf8.prev(&d)) {
		case let r: rune          => { it.offs = d.offs; return r; };
		case let dn: utf8.done    => return dn;
		case let m:  utf8.more    => abort("strings.move: invalid UTF-8");
		case let e:  utf8.invalid => abort("strings.move: invalid UTF-8");
		};
	};
};

// next — advance the iterator one rune. Forward iterators step
// through utf8.next; reverse iterators (riter) step backward through
// utf8.prev. Returns utf8.done at end-of-walk. ref/hare/strings/iter.ha:45.
export fn next(it: *iterator) (rune | utf8.done) = {
	return move(!it.reverse, it);
};

// prev — step back one rune. Dual to next: on a forward iterator
// this walks utf8.prev; on a reverse iterator (riter) it walks
// utf8.next. ref/hare/strings/iter.ha:49.
export fn prev(it: *iterator) (rune | utf8.done) = {
	return move(it.reverse, it);
};

// iterstr — borrowed view of the bytes remaining in the iterator's
// walk direction. Forward iter: bytes from offs to end; reverse iter:
// bytes from start to offs. ref/hare/strings/iter.ha:63.
export fn iterstr(it: *iterator) str = {
	let r: []u8;
	if (it.reverse) {
		r = it.src[0:it.offs];
	} else {
		r = it.src[it.offs:it.src.len];
	};
	return frombytes(r);
};

// slice — borrowed substring between two iterator positions.
// ref/hare/strings/iter.ha:75. Hare passes `*iterator` directly where
// `*utf8::decoder` is expected via anonymous-embed coercion; ww has
// no anonymous embed, so we reconstruct a local utf8.decoder for each
// endpoint and forward — same pattern as `move` above.
export fn slice(begin: *iterator, end: *iterator) str = {
	let b: utf8.decoder;
	b.src = begin.src;
	b.offs = begin.offs;
	let e: utf8.decoder;
	e.src = end.src;
	e.offs = end.offs;
	return frombytes(utf8.slice(&b, &e));
};

// position — byte-wise offset of the iterator in its source.
// ref/hare/strings/iter.ha:82.
export fn position(it: *iterator) i32 = {
	return it.offs;
};

// tokenizer — re-export of bytes.tokenizer. ref/hare/strings/tokenize.ha:7.
// First cross-module type alias in tree; needs #22's transitive
// alias-chain unwrap (cstage type_chase_named + wwstage
// structlookupchain) to walk struct fields through the chain.
export type tokenizer = bytes.tokenizer;

// tokenize — yield substrings of `s` split on any byte in `delim`.
// Leading / trailing / adjacent delims yield empty tokens. `s` and
// `delim` are borrowed; caller keeps them live for the tokenizer's
// lifetime. ref/hare/strings/tokenize.ha:32. ASCII-only delim
// asserted per Hare lines 35-37: a multibyte rune in delim would
// split on a single continuation byte and yield invalid UTF-8.
export fn tokenize(s: str, delim: str) tokenizer = {
	let d: []u8 = toutf8(delim);
	let i: i32 = 0;
	for (i < d.len) {
		assert((d[i] & 0x80u8) == 0u8,
			"strings.tokenize cannot tokenize on non-ASCII delimiters");
		i += 1;
	};
	return bytes.tokenize(toutf8(s), d...);
};

// rtokenize — reverse-direction counterpart to [[tokenize]]. First
// next_token yields the last token, last yields the first.
// ref/hare/strings/tokenize.ha:44.
export fn rtokenize(s: str, delim: str) tokenizer = {
	let d: []u8 = toutf8(delim);
	let i: i32 = 0;
	for (i < d.len) {
		assert((d[i] & 0x80u8) == 0u8,
			"strings.rtokenize cannot tokenize on non-ASCII delimiters");
		i += 1;
	};
	return bytes.rtokenize(toutf8(s), d...);
};

// next_token — current token, advancing the cursor.
// ref/hare/strings/tokenize.ha:62.
export fn next_token(s: *tokenizer) (str | bytes.done) = {
	let b: *bytes.tokenizer = s: *bytes.tokenizer;
	match (bytes.next_token(b)) {
	case let v: []u8 => return frombytes(v);
	case bytes.done  => { let d: bytes.done; return d; };
	};
};

// peek_token — current token without advancing.
// ref/hare/strings/tokenize.ha:71.
export fn peek_token(s: *tokenizer) (str | bytes.done) = {
	let b: *bytes.tokenizer = s: *bytes.tokenizer;
	match (bytes.peek_token(b)) {
	case let v: []u8 => return frombytes(v);
	case bytes.done  => { let d: bytes.done; return d; };
	};
};

// remaining_tokens — unconsumed portion of the input ahead of the
// cursor. ref/hare/strings/tokenize.ha:79.
export fn remaining_tokens(s: *tokenizer) str = {
	let b: *bytes.tokenizer = s: *bytes.tokenizer;
	return frombytes(bytes.remaining_tokens(b));
};

// cut — split `in` along the first instance of `delim`, returning the
// portions before and after it. When `delim` is absent the whole input
// is the first half and the second is empty. Both halves are borrowed
// from `in`; caller ensures `delim` is non-empty.
// ref/hare/strings/tokenize.ha:288.
export fn cut(in: str, delim: str) (str, str) = {
	let (a, b) = bytes.cut(toutf8(in), toutf8(delim));
	return (frombytes(a), frombytes(b));
};

// rcut — like [[cut]] but split along the LAST instance of `delim`.
// ref/hare/strings/tokenize.ha:302.
export fn rcut(in: str, delim: str) (str, str) = {
	let (a, b) = bytes.rcut(toutf8(in), toutf8(delim));
	return (frombytes(a), frombytes(b));
};

// splitn — split `in` on any byte in `delim`, returning up to `n`
// tokens via forward iteration. The trailing slot (when more than
// `n - 1` tokens exist) holds the unconsumed remainder. Strings
// within the result are borrowed from `in`.
//
// The caller frees the returned slice via
// `os.free(r.ptr: *void, (r.cap: u64) * size(str): u64)`.
//
// Hare's `([]str | nomem)` collapses to `[]str` here: ww os.alloc
// has no recoverable failure path. Same precedent as
// shlex.split / bytes.splitn.
//
// ref/hare/strings/tokenize.ha:172.
export fn splitn(in: str, delim: str, n: i32) []str = {
	let toks: []str;
	toks.ptr = nil: *str;
	toks.len = 0;
	toks.cap = 0;
	let tok: tokenizer = tokenize(in, delim);
	let i: i32 = 0;
	for (i < n - 1) {
		match (next_token(&tok)) {
		case let s: str => { append(toks, s); };
		case bytes.done => { return toks; };
		};
		i += 1;
	};
	match (peek_token(&tok)) {
	case bytes.done  => void;
	case let pk: str => {
		let r: str = remaining_tokens(&tok);
		append(toks, r);
	};
	};
	return toks;
};

// rsplitn — reverse-direction counterpart to [[splitn]]: tokens are
// collected from the end of `in`. The trailing slot holds the
// unconsumed prefix (everything before the n-th-from-last delim hit).
//
// When the input has fewer than n tokens, the `done` short-circuit
// returns toks UN-reversed (in last-token-first order). Mirrors Hare
// at ref/hare/strings/tokenize.ha:219-224 where the in-place reverse
// step is gated behind the n-1 loop running to completion.
//
// ref/hare/strings/tokenize.ha:200.
export fn rsplitn(in: str, delim: str, n: i32) []str = {
	let toks: []str;
	toks.ptr = nil: *str;
	toks.len = 0;
	toks.cap = 0;
	let tok: tokenizer = rtokenize(in, delim);
	let i: i32 = 0;
	for (i < n - 1) {
		match (next_token(&tok)) {
		case let s: str => { append(toks, s); };
		case bytes.done => { return toks; };
		};
		i += 1;
	};
	match (peek_token(&tok)) {
	case bytes.done  => void;
	case let pk: str => {
		let r: str = remaining_tokens(&tok);
		append(toks, r);
	};
	};

	// In-place reverse so callers see argv-order, matching Hare
	// (ref/hare/strings/tokenize.ha:220). Element copy is field-wise
	// through `*str` because `toks[i] = toks[j]` (full 16B str store)
	// lands in the multi-word-store gap noted at cmd/w6c/cgen.c:6515.
	let a: i32 = 0;
	let b: i32 = toks.len - 1;
	for (a < b) {
		let pa: *str = &toks.ptr[a];
		let pb: *str = &toks.ptr[b];
		let tp: *u8 = pa.ptr;
		let tl: i32 = pa.len;
		pa.ptr = pb.ptr;
		pa.len = pb.len;
		pb.ptr = tp;
		pb.len = tl;
		a += 1;
		b -= 1;
	};
	return toks;
};

// split — full split of `in` on `delim` (no token cap). Mirrors
// `splitn(in, delim, types::SIZE_MAX)`. ww uses `types.I32_MAX`
// because the index type is i32 (lib/CLAUDE.md).
//
// ref/hare/strings/tokenize.ha:242.
export fn split(in: str, delim: str) []str = {
	return splitn(in, delim, types.I32_MAX);
};

// lpad — left-pad `s` with `p` rune until the result reaches `maxlen`
// bytes. Length comparison is BYTES, mirroring Hare's `len(s) >= maxlen`
// at ref/hare/strings/pad.ha:9. A multibyte `p` whose encoded width
// doesn't divide `maxlen - s.len` evenly leaves a trailing pad byte
// pair sliced mid-codepoint at byte `maxlen-1`, exactly as Hare's
// `res[..maxlen]` does (ref/hare/strings/pad.ha:20). When
// `(maxlen - s.len) * pad.len >= maxlen` (multibyte pad overflows the
// budget), `s` is entirely sliced off — same as Hare. Caller releases
// with `os.free(r.ptr, r.len: u64)`. Hare's `nomem` return is dropped:
// `os.alloc` aborts on OOM. Buf size == r.len keeps the free-contract
// shape of [[dup]] / [[concat]] / [[join]]; Hare's `alloc([], maxlen)!`
// over-allocs via append then slices, but Hare's slice-free recovers
// the true capacity from the heap allocator (rt/ensure.ha:24), which
// ww's munmap-based `os.free` cannot do.
export fn lpad(s: str, p: rune, maxlen: i32) str = {
	if (s.len >= maxlen) { return dup(s); };
	let scratch: [4]u8;
	let pad: []u8 = runebytes(scratch[0:4], p);
	let buf: []u8 = alloc([], maxlen: u64)!;
	let padwrite: i32 = (maxlen - s.len) * pad.len;
	if (padwrite > maxlen) { padwrite = maxlen; };
	let off: i32 = 0;
	for (off < padwrite) {
		buf[off] = pad.ptr[off % pad.len];
		off += 1;
	};
	let k: i32 = 0;
	let srem: i32 = maxlen - off;
	if (srem > s.len) { srem = s.len; };
	for (k < srem) {
		buf[off + k] = s[k];
		k += 1;
	};
	buf.len = maxlen;
	return frombytes(buf);
};

// replace — fresh allocation of `s` with every non-overlapping
// occurrence of `needle` replaced by `target`. Caller releases with
// `os.free(r.ptr, r.len: u64)`. ref/hare/strings/replace.ha:8 (#4).
//
// Hare delegates to [[multireplace]] with a single pair; ww has no
// `(str, str)` variadic shape today (#39), so this is a standalone
// two-pass implementation: pass 1 counts matches to size the result,
// pass 2 copies chunks and `target` into a single fresh buffer.
// Single nomem path (the `alloc([], total)?`) preserves Hare's
// signature without a per-write `append(...)?` (ww's append builtin
// aborts on OOM, #11). Empty `needle` would hasprefix-match every
// position with a zero stride — same infinite loop Hare exhibits at
// ref/hare/strings/replace.ha:31; not gated.
export fn replace(s: str, needle: str, target: str) (str | nomem) = {
	let sb: []u8 = toutf8(s);
	let nb: []u8 = toutf8(needle);
	let tb: []u8 = toutf8(target);
	let count: i32 = 0;
	let i: i32 = 0;
	for (i < sb.len) {
		if (bytes.hasprefix(sb[i:sb.len], nb)) {
			count += 1;
			i += nb.len;
		} else {
			i += 1;
		};
	};
	let total: i32 = sb.len + count * (tb.len - nb.len);
	if (total == 0) {
		let r: str;
		r.ptr = nil;
		r.len = 0;
		return r;
	};
	let res: []u8 = alloc([], total)?;
	let off: i32 = 0;
	i = 0;
	for (i < sb.len) {
		if (bytes.hasprefix(sb[i:sb.len], nb)) {
			let j: i32 = 0;
			for (j < tb.len) {
				res.ptr[off + j] = tb.ptr[j];
				j += 1;
			};
			off += tb.len;
			i += nb.len;
		} else {
			res.ptr[off] = sb.ptr[i];
			off += 1;
			i += 1;
		};
	};
	res.len = total;
	return frombytes(res);
};

// rpad — right-pad `s` with `p` rune until the result reaches `maxlen`
// bytes. Symmetric with [[lpad]]. ref/hare/strings/pad.ha:39.
export fn rpad(s: str, p: rune, maxlen: i32) str = {
	if (s.len >= maxlen) { return dup(s); };
	let scratch: [4]u8;
	let pad: []u8 = runebytes(scratch[0:4], p);
	let buf: []u8 = alloc([], maxlen: u64)!;
	let k: i32 = 0;
	for (k < s.len) {
		buf[k] = s[k];
		k += 1;
	};
	let padwrite: i32 = maxlen - s.len;
	let i: i32 = 0;
	for (i < padwrite) {
		buf[s.len + i] = pad.ptr[i % pad.len];
		i += 1;
	};
	buf.len = maxlen;
	return frombytes(buf);
};

// selfhost/cmd/w6a/opcodes.ww — types + constants shared across the
// w6a port. Mirrors cmd/w6a/a.h and cmd/w6c/6.out.h.

package w6a;

// ---- registers + operand kinds (from 6.out.h) -------------------------
// These must stay numerically aligned with the C enum so that ww-cgen
// output (which reads them via `D_AX(SB)` etc.) lands on the same
// integers when read by ww-w6a.
def D_NONE: i32 = 0;

def D_AX: i32 = 1;
def D_CX: i32 = 2;
def D_DX: i32 = 3;
def D_BX: i32 = 4;
def D_SP: i32 = 5;
def D_BP: i32 = 6;
def D_SI: i32 = 7;
def D_DI: i32 = 8;
def D_R8:  i32 = 9;
def D_R9:  i32 = 10;
def D_R10: i32 = 11;
def D_R11: i32 = 12;
def D_R12: i32 = 13;
def D_R13: i32 = 14;
def D_R14: i32 = 15;
def D_R15: i32 = 16;

def D_X0:  i32 = 17;
def D_X1:  i32 = 18;
def D_X2:  i32 = 19;
def D_X3:  i32 = 20;
def D_X4:  i32 = 21;
def D_X5:  i32 = 22;
def D_X6:  i32 = 23;
def D_X7:  i32 = 24;
def D_X8:  i32 = 25;
def D_X9:  i32 = 26;
def D_X10: i32 = 27;
def D_X11: i32 = 28;
def D_X12: i32 = 29;
def D_X13: i32 = 30;
def D_X14: i32 = 31;
def D_X15: i32 = 32;

def D_PSP: i32 = 33;
def D_PFP: i32 = 34;
def D_PSB: i32 = 35;

def D_CONST:  i32 = 36;
def D_BRANCH: i32 = 37;
def D_EXTERN: i32 = 38;
def D_INDIR:  i32 = 39;

// ---- opcodes ----------------------------------------------------------
def A_NOP: i32 = 0;
def A_TEXT: i32 = 1;
def A_DATA: i32 = 2;
def A_GLOBL: i32 = 3;
def A_END: i32 = 4;

def A_MOVQ: i32 = 5;
def A_MOVL: i32 = 6;
def A_MOVB: i32 = 7;
def A_MOVZBQ: i32 = 8;
def A_MOVSXD: i32 = 9;
def A_MOVW: i32 = 62;
def A_MOVZWQ: i32 = 63;
def A_MOVSWQ: i32 = 64;
def A_MOVSBQ: i32 = 65;

def A_MOVSD: i32 = 10;
def A_ADDSD: i32 = 11;
def A_SUBSD: i32 = 12;
def A_MULSD: i32 = 13;
def A_DIVSD: i32 = 14;
def A_UCOMISD: i32 = 15;
def A_CVTTSD2SI: i32 = 16;
def A_CVTSI2SD: i32 = 17;

def A_MOVSS: i32 = 18;
def A_ADDSS: i32 = 19;
def A_SUBSS: i32 = 20;
def A_MULSS: i32 = 21;
def A_DIVSS: i32 = 22;
def A_UCOMISS: i32 = 23;
def A_CVTTSS2SI: i32 = 24;
def A_CVTSI2SS: i32 = 25;
def A_CVTSD2SS: i32 = 26;
def A_CVTSS2SD: i32 = 27;

def A_ADDQ: i32 = 28;
def A_SUBQ: i32 = 29;
def A_IMULQ: i32 = 30;
def A_IDIVQ: i32 = 31;
def A_DIVQ: i32 = 32;
def A_NEGQ: i32 = 33;
def A_NOTQ: i32 = 34;
def A_ANDQ: i32 = 35;
def A_ORQ: i32 = 36;
def A_XORQ: i32 = 37;
def A_SHLQ: i32 = 38;
def A_SHRQ: i32 = 39;
def A_CMPQ: i32 = 40;

def A_PUSHQ: i32 = 41;
def A_POPQ: i32 = 42;
def A_LEAQ: i32 = 43;

def A_CALL: i32 = 44;
def A_RET:  i32 = 45;
def A_JMP:  i32 = 46;
def A_JE:   i32 = 47;
def A_JNE:  i32 = 48;
def A_JL:   i32 = 49;
def A_JLE:  i32 = 50;
def A_JG:   i32 = 51;
def A_JGE:  i32 = 52;
def A_JB:   i32 = 53;
def A_JBE:  i32 = 54;
def A_JA:   i32 = 55;
def A_JAE:  i32 = 56;
def A_JZ:   i32 = 57;
def A_JNZ:  i32 = 58;
// 67 (next free above A_CQO=66): appended so the existing A_MOV*/
// A_SYSCALL/A_DATAW/A_DATAR/A_CQO numbers stay put. Jump on
// parity (PF=1): UCOMISD unordered (#97).
def A_JP:   i32 = 67;
// #136: arithmetic right-shift, sign-extends MSB. SHR injects
// zeros and is wrong for signed operands; cgen routes signed
// `>>` / `>>=` through SAR after this opcode landed.
def A_SARQ: i32 = 68;

def A_SYSCALL: i32 = 59;

// Writable data + reloc-only data. Mirror cmd/w6c/6.out.h.
// A_DATAW: bytes land in .data (RW) instead of .text.
// A_DATAR: record an R_X86_64_64 reloc at a .data slot, patched
//          to a target symbol's runtime VA at link time.
def A_DATAW: i32 = 60;
def A_DATAR: i32 = 61;

// REX.W 99 — sign-extend RAX into RDX:RAX. Pairs with IDIVQ for
// signed division; pendant to the MOVQ $0, DX zero-fill that pairs
// with DIVQ.
def A_CQO: i32 = 66;

// ---- structs (mirror cmd/w6a/a.h) --------------------------------------

type aoperand = struct {
	atype:  i32,	// D_NONE / D_AX..D_R15 / D_CONST / D_INDIR / D_EXTERN / D_BRANCH
	reg:    i32,
	offset: i64,
	asym:   str,
};

// `from` and `to` are pointer-to-aoperand (rather than embedded).
// The C cgen doesn't support chained-dot through embedded value
// fields, so allocating each operand once per prog lets us write
// `p.to.atype` directly.
type aprog = struct {
	as_:   i32,
	from:  *aoperand,
	to:    *aoperand,
	line:  i32,
	label: str,
	link:  *aprog,
	bytes: *u8,	// payload for A_DATA
	nbytes: u64,
};

type asym = struct {
	name:      str,
	defined:   i32,
	istext:    i32,
	isdata:    i32,	// mutually exclusive with istext; DATAW symbols
	isglobal:  i32,
	addr:      u64,	// offset within its section (.text or .data)
	idx:       i32,
	snext:     *asym,
};

type areloc = struct {
	off:    u64,
	section: i32,	// 0 = .text, 1 = .data
	kind:   i32,
	asy:    *asym,
	addend: i64,
	rnext:  *areloc,
};

type afixup = struct {
	off:    u64,	// where the rel32 lands in .text
	label:  str,
	fnext:  *afixup,
};

type asm_ = struct {
	file:    str,
	src:     *u8,
	srclen:  u64,
	pos:     u64,
	line:    i32,

	head:    *aprog,
	tail:    *aprog,

	text:    *u8,
	textcap: u64,
	textlen: u64,

	// Writable .data. Empty unless any DATAW directive was seen;
	// obj.ww emits the extra section conditionally so .o output
	// stays byte-identical for inputs that don't use DATAW (test
	// 991 byte-diff invariant).
	data:    *u8,
	datacap: u64,
	datalen: u64,

	syms:    *asym,
	relocs:  *areloc,
	fixups:  *afixup,

	errs:    i32,
};

// selfhost/cmd/w6a/lex.ww — port of cmd/w6a/lex.c.
//
// Character-level helpers for w6a's line-oriented parser. The parser
// itself is in parse.ww; here we keep tokenisers for identifiers and
// numbers so parse.ww stays focused on syntax.

package w6a;

export fn isidstart(c: i32) bool = {
	if (c == 95) { return true; };
	if (c >= 65) { if (c <= 90)  { return true; }; };	// A-Z
	if (c >= 97) { if (c <= 122) { return true; }; };	// a-z
	return false;
};

export fn isidcont(c: i32) bool = {
	if (isidstart(c)) { return true; };
	if (c >= 48) { if (c <= 57) { return true; }; };	// 0-9
	if (c == 46) { return true; };				// .
	return false;
};

// parsenum — read a leading [+-]?[0x|0X|0]?digits from p[0..n-1].
// Returns (value, consumed). Stops at first non-digit.
// Plain Plan 9-style: $123 / $0x1f / $-7. Decimal default; 0x prefix
// for hex; 0 prefix for octal when followed by a digit (else just 0).
export fn parsenum(p: *u8, n: u64) (i64, u64) = {
	let i: u64 = 0u64;
	let neg: bool = false;
	if (i < n) {
		if (p[i] == 45u8) { neg = true; i += 1u64; }
		else { if (p[i] == 43u8) { i += 1u64; }; };
	};
	let base: i64 = 10i64;
	if (i + 1u64 < n) {
		if (p[i] == 48u8) {
			if (p[i + 1u64] == 120u8) { base = 16i64; i += 2u64; }
			else { if (p[i + 1u64] == 88u8) { base = 16i64; i += 2u64; }
			else { if (p[i + 1u64] >= 48u8) { if (p[i + 1u64] <= 55u8) {
				base = 8i64; i += 1u64;
			};};};};
		};
	};
	let v: i64 = 0i64;
	let scan: bool = true;
	for (scan) {
		if (i >= n) { scan = false; }
		else {
			let c: u8 = p[i];
			let d: i64 = -1i64;
			if (c >= 48u8) { if (c <= 57u8) { d = (c - 48u8): i64; }; };
			if (d < 0i64) {
				if (base == 16i64) {
					if (c >= 97u8) { if (c <= 102u8) { d = (c - 97u8): i64 + 10i64; }; };
					if (c >= 65u8) { if (c <= 70u8)  { d = (c - 65u8): i64 + 10i64; }; };
				};
			};
			if (d < 0i64) { scan = false; }
			else { if (d >= base) { scan = false; }
			else {
				v = v * base + d;
				i += 1u64;
			}; };
		};
	};
	if (neg) { v = -v; };
	return v, i;
};

// selfhost/cmd/w6a/parse.ww — port of cmd/w6a/parse.c.
//
// Line-oriented parser for the asm subset emitted by w6c.
// Grammar:
//   line  := blank | comment | label | text | instr
//   blank := /^\s*$/
//   comment := /^\s*\/\/.*$/
//   label := /^IDENT:$/
//   text  := TEXT name,$framesize
//   instr := \tMNEM\t[OP1[, OP2]]
//   OP    := $NUM | REG | NUM(REG) | (REG) | name(SB) | label

package w6a;

import os;
import strings;
import lex;
import opcodes;

fn streqlit(p: *u8, n: u64, lit: str) bool = {
	if (n != lit.len: u64) { return false; };
	let i: u64 = 0u64;
	for (i < n) {
		let li: i32 = i: i32;
		if (p[i] != lit[li]) { return false; };
		i += 1u64;
	};
	return true;
};

// opcodelookup — name (length-bounded *u8) → A_*. Returns 0 (A_NOP)
// if not found.
fn opcodelookup(p: *u8, n: u64) i32 = {
	if (streqlit(p, n, "MOVQ"))    { return A_MOVQ; };
	if (streqlit(p, n, "MOVL"))    { return A_MOVL; };
	if (streqlit(p, n, "MOVW"))    { return A_MOVW; };
	if (streqlit(p, n, "MOVB"))    { return A_MOVB; };
	if (streqlit(p, n, "MOVZBQ"))  { return A_MOVZBQ; };
	if (streqlit(p, n, "MOVZWQ"))  { return A_MOVZWQ; };
	if (streqlit(p, n, "MOVSXD"))  { return A_MOVSXD; };
	if (streqlit(p, n, "MOVSWQ"))  { return A_MOVSWQ; };
	if (streqlit(p, n, "MOVSBQ"))  { return A_MOVSBQ; };
	if (streqlit(p, n, "MOVSD"))   { return A_MOVSD; };
	if (streqlit(p, n, "ADDSD"))   { return A_ADDSD; };
	if (streqlit(p, n, "SUBSD"))   { return A_SUBSD; };
	if (streqlit(p, n, "MULSD"))   { return A_MULSD; };
	if (streqlit(p, n, "DIVSD"))   { return A_DIVSD; };
	if (streqlit(p, n, "UCOMISD")) { return A_UCOMISD; };
	if (streqlit(p, n, "CVTTSD2SI")) { return A_CVTTSD2SI; };
	if (streqlit(p, n, "CVTSI2SD")) { return A_CVTSI2SD; };
	if (streqlit(p, n, "MOVSS"))   { return A_MOVSS; };
	if (streqlit(p, n, "ADDSS"))   { return A_ADDSS; };
	if (streqlit(p, n, "SUBSS"))   { return A_SUBSS; };
	if (streqlit(p, n, "MULSS"))   { return A_MULSS; };
	if (streqlit(p, n, "DIVSS"))   { return A_DIVSS; };
	if (streqlit(p, n, "UCOMISS")) { return A_UCOMISS; };
	if (streqlit(p, n, "CVTTSS2SI")) { return A_CVTTSS2SI; };
	if (streqlit(p, n, "CVTSI2SS")) { return A_CVTSI2SS; };
	if (streqlit(p, n, "CVTSD2SS")) { return A_CVTSD2SS; };
	if (streqlit(p, n, "CVTSS2SD")) { return A_CVTSS2SD; };
	if (streqlit(p, n, "ADDQ"))    { return A_ADDQ; };
	if (streqlit(p, n, "SUBQ"))    { return A_SUBQ; };
	if (streqlit(p, n, "IMULQ"))   { return A_IMULQ; };
	if (streqlit(p, n, "IDIVQ"))   { return A_IDIVQ; };
	if (streqlit(p, n, "DIVQ"))    { return A_DIVQ; };
	if (streqlit(p, n, "CQO"))     { return A_CQO; };
	if (streqlit(p, n, "NEGQ"))    { return A_NEGQ; };
	if (streqlit(p, n, "NOTQ"))    { return A_NOTQ; };
	if (streqlit(p, n, "ANDQ"))    { return A_ANDQ; };
	if (streqlit(p, n, "ORQ"))     { return A_ORQ; };
	if (streqlit(p, n, "XORQ"))    { return A_XORQ; };
	if (streqlit(p, n, "SHLQ"))    { return A_SHLQ; };
	if (streqlit(p, n, "SHRQ"))    { return A_SHRQ; };
	if (streqlit(p, n, "SARQ"))    { return A_SARQ; };
	if (streqlit(p, n, "CMPQ"))    { return A_CMPQ; };
	if (streqlit(p, n, "PUSHQ"))   { return A_PUSHQ; };
	if (streqlit(p, n, "POPQ"))    { return A_POPQ; };
	if (streqlit(p, n, "LEAQ"))    { return A_LEAQ; };
	if (streqlit(p, n, "CALL"))    { return A_CALL; };
	if (streqlit(p, n, "RET"))     { return A_RET; };
	if (streqlit(p, n, "JMP"))     { return A_JMP; };
	if (streqlit(p, n, "JE"))      { return A_JE; };
	if (streqlit(p, n, "JNE"))     { return A_JNE; };
	if (streqlit(p, n, "JL"))      { return A_JL; };
	if (streqlit(p, n, "JLE"))     { return A_JLE; };
	if (streqlit(p, n, "JG"))      { return A_JG; };
	if (streqlit(p, n, "JGE"))     { return A_JGE; };
	if (streqlit(p, n, "JB"))      { return A_JB; };
	if (streqlit(p, n, "JBE"))     { return A_JBE; };
	if (streqlit(p, n, "JA"))      { return A_JA; };
	if (streqlit(p, n, "JAE"))     { return A_JAE; };
	if (streqlit(p, n, "JZ"))      { return A_JZ; };
	if (streqlit(p, n, "JNZ"))     { return A_JNZ; };
	if (streqlit(p, n, "JP"))      { return A_JP; };
	if (streqlit(p, n, "SYSCALL")) { return A_SYSCALL; };
	if (streqlit(p, n, "TEXT"))    { return A_TEXT; };
	if (streqlit(p, n, "DATA"))    { return A_DATA; };
	if (streqlit(p, n, "DATAW"))   { return A_DATAW; };
	if (streqlit(p, n, "DATAR"))   { return A_DATAR; };
	return A_NOP;
};

// reglookup — name → D_*. Returns D_NONE if not found.
fn reglookup(p: *u8, n: u64) i32 = {
	if (streqlit(p, n, "AX")) { return D_AX; };
	if (streqlit(p, n, "BX")) { return D_BX; };
	if (streqlit(p, n, "CX")) { return D_CX; };
	if (streqlit(p, n, "DX")) { return D_DX; };
	if (streqlit(p, n, "SP")) { return D_SP; };
	if (streqlit(p, n, "BP")) { return D_BP; };
	if (streqlit(p, n, "SI")) { return D_SI; };
	if (streqlit(p, n, "DI")) { return D_DI; };
	if (streqlit(p, n, "R8"))  { return D_R8; };
	if (streqlit(p, n, "R9"))  { return D_R9; };
	if (streqlit(p, n, "R10")) { return D_R10; };
	if (streqlit(p, n, "R11")) { return D_R11; };
	if (streqlit(p, n, "R12")) { return D_R12; };
	if (streqlit(p, n, "R13")) { return D_R13; };
	if (streqlit(p, n, "R14")) { return D_R14; };
	if (streqlit(p, n, "R15")) { return D_R15; };
	if (streqlit(p, n, "X0"))  { return D_X0; };
	if (streqlit(p, n, "X1"))  { return D_X1; };
	if (streqlit(p, n, "X2"))  { return D_X2; };
	if (streqlit(p, n, "X3"))  { return D_X3; };
	if (streqlit(p, n, "X4"))  { return D_X4; };
	if (streqlit(p, n, "X5"))  { return D_X5; };
	if (streqlit(p, n, "X6"))  { return D_X6; };
	if (streqlit(p, n, "X7"))  { return D_X7; };
	if (streqlit(p, n, "X8"))  { return D_X8; };
	if (streqlit(p, n, "X9"))  { return D_X9; };
	if (streqlit(p, n, "X10")) { return D_X10; };
	if (streqlit(p, n, "X11")) { return D_X11; };
	if (streqlit(p, n, "X12")) { return D_X12; };
	if (streqlit(p, n, "X13")) { return D_X13; };
	if (streqlit(p, n, "X14")) { return D_X14; };
	if (streqlit(p, n, "X15")) { return D_X15; };
	if (streqlit(p, n, "SB"))  { return D_PSB; };
	if (streqlit(p, n, "FP"))  { return D_PFP; };
	return D_NONE;
};

export fn init(a: *asm_, file: str, src: *u8, len: u64) void = {
	a.file = file;
	a.src = src;
	a.srclen = len;
	a.pos = 0u64;
	a.line = 1;
	a.head = nil;
	a.tail = nil;
	a.text = nil;
	a.textcap = 0u64;
	a.textlen = 0u64;
	a.syms = nil;
	a.relocs = nil;
	a.fixups = nil;
	a.errs = 0;
};

export fn intern(a: *asm_, name: str) *asym = {
	let s: *asym = a.syms;
	for (s != nil) {
		if (strings.compare(s.name, name) == 0) { return s; };
		s = s.snext;
	};
	let n: *asym = alloc(asym { name = name, snext = a.syms })!;
	a.syms = n;
	return n;
};

fn perr(a: *asm_, msg: str) void = {
	let pfx: str = "w6a: ";
	os.write(2, pfx.ptr, pfx.len: u64);
	let f: str = a.file;
	os.write(2, f.ptr, f.len: u64);
	let sep: str = ": ";
	os.write(2, sep.ptr, sep.len: u64);
	os.write(2, msg.ptr, msg.len: u64);
	let nl: str = "\n";
	os.write(2, nl.ptr, nl.len: u64);
	a.errs += 1;
};

// dupstr — copy n bytes from p into a fresh heap str.
fn dupstr(p: *u8, n: u64) str = {
	let view: str;
	view.ptr = p;
	view.len = n: i32;
	return strings.dup(view);
};

// ---- line iteration & whitespace --------------------------------------

// Read next line into a fresh heap buffer; returns (ptr, len) or (nil,0)
// at EOF. Advances a.pos past the newline.
fn nextline(a: *asm_) (*u8, u64) = {
	if (a.pos >= a.srclen) { return nil, 0u64; };
	let start: u64 = a.pos;
	for (a.pos < a.srclen) {
		if (a.src[a.pos] == '\n') { a.pos = a.pos; a.pos += 0u64; }	// no-op; explicit break via condition
		else { a.pos += 1u64; continue; };
		// hit newline
		let n: u64 = a.pos - start;
		let buf: []u8 = alloc([], n + 1u64)!;
		let i: u64 = 0u64;
		for (i < n) { buf[i] = a.src[start + i]; i += 1u64; };
		buf[n] = 0u8;
		a.pos += 1u64;	// skip newline
		return buf.ptr, n;
	};
	// EOF without trailing newline
	let n: u64 = a.pos - start;
	if (n == 0u64) { return nil, 0u64; };
	let buf: []u8 = alloc([], n + 1u64)!;
	let i: u64 = 0u64;
	for (i < n) { buf[i] = a.src[start + i]; i += 1u64; };
	buf[n] = 0u8;
	return buf.ptr, n;
};

fn skipws(p: *u8, off: u64, n: u64) u64 = {
	let i: u64 = off;
	for (i < n) {
		if (p[i] != ' ') { if (p[i] != '\t') { return i; }; };
		i += 1u64;
	};
	return i;
};

// parseoperand — parse one operand from p[off..n), populate out.
// Returns new offset (clamped to n on error).
fn parseoperand(a: *asm_, p: *u8, offin: u64, n: u64, out: *aoperand) u64 = {
	let off: u64 = skipws(p, offin, n);
	out.atype = D_NONE;
	out.reg = 0;
	out.offset = 0i64;
	let empty: str;
	empty.ptr = nil; empty.len = 0;
	out.asym = empty;
	if (off >= n) { return off; };
	let c0: u8 = p[off];

	// $NUM
	if (c0 == '$') {
		off += 1u64;
		let v: i64;
		let used: u64;
		v, used = parsenum(p + off, n - off);
		out.atype = D_CONST;
		out.offset = v;
		return off + used;
	};

	// (REG)
	if (c0 == '(') {
		off += 1u64;
		let rstart: u64 = off;
		for (off < n) {
			if (p[off] == ')') { off = off; off += 0u64; }	// no-op marker
			else { off += 1u64; continue; };
			let rn: u64 = off - rstart;
			let r: i32 = reglookup(p + rstart, rn);
			if (r == 0) { perr(a, "bad register in indirect"); return n; };
			out.atype = D_INDIR;
			out.reg = r;
			out.offset = 0i64;
			return off + 1u64;	// past ')'
		};
		perr(a, "missing ')' in indirect");
		return n;
	};

	// number(REG) — possibly signed — or bare $NUM-less constant
	let cur: u64 = off;
	let isnum: bool = false;
	if (cur < n) {
		if (p[cur] == '-') { isnum = true; }
		else { if (p[cur] >= '0') { if (p[cur] <= '9') { isnum = true; }; }; };
	};
	if (isnum) {
		let v: i64;
		let used: u64;
		v, used = parsenum(p + off, n - off);
		let after: u64 = off + used;
		if (after < n) { if (p[after] == '(') {
			let rstart: u64 = after + 1u64;
			let cur2: u64 = rstart;
			for (cur2 < n) {
				if (p[cur2] == ')') { cur2 = cur2; cur2 += 0u64; }
				else { cur2 += 1u64; continue; };
				let rn: u64 = cur2 - rstart;
				let r: i32 = reglookup(p + rstart, rn);
				if (r == 0) { perr(a, "bad register"); return n; };
				out.atype = D_INDIR;
				out.reg = r;
				out.offset = v;
				return cur2 + 1u64;
			};
			perr(a, "missing ')'");
			return n;
		};};
		out.atype = D_CONST;
		out.offset = v;
		return after;
	};

	// IDENT — register, symbol(SB), symbol+disp(SB), or branch label
	if (isidstart(c0: i32)) {
		let istart: u64 = off;
		for (off < n) {
			if (isidcont(p[off]: i32)) { off += 1u64; continue; };
			off = off; off += 0u64;	// loop break
			let in_: u64 = off - istart;
			// Optional `+disp` between the ident and `(SB)`. Used
			// by DATAR to address bytes within a previously-defined
			// .data slot (e.g. `DATAR s+8(SB),...`).
			let symdisp: i64 = 0i64;
			if (off < n) { if (p[off] == '+') {
				off += 1u64;
				let v: i64;
				let used: u64;
				v, used = parsenum(p + off, n - off);
				symdisp = v;
				off += used;
			};};
			// IDENT(SB) — external
			if (off < n) { if (p[off] == '(') {
				let rstart: u64 = off + 1u64;
				let cur2: u64 = rstart;
				for (cur2 < n) {
					if (p[cur2] == ')') { cur2 = cur2; cur2 += 0u64; }
					else { cur2 += 1u64; continue; };
					let rn: u64 = cur2 - rstart;
					let r: i32 = reglookup(p + rstart, rn);
					if (r == D_PSB) {
						out.atype = D_EXTERN;
						out.asym = dupstr(p + istart, in_);
						out.offset = symdisp;
					} else {
						out.atype = D_INDIR;
						out.reg = r;
						out.offset = 0i64;
					};
					return cur2 + 1u64;
				};
				perr(a, "missing ')'");
				return n;
			};};
			let r: i32 = reglookup(p + istart, in_);
			if (r != D_NONE) {
				out.atype = r;
				return off;
			};
			out.atype = D_BRANCH;
			out.asym = dupstr(p + istart, in_);
			return off;
		};
		// EOF inside ident
		let in_: u64 = off - istart;
		let r: i32 = reglookup(p + istart, in_);
		if (r != D_NONE) { out.atype = r; return off; };
		out.atype = D_BRANCH;
		out.asym = dupstr(p + istart, in_);
		return off;
	};

	perr(a, "unrecognised operand");
	return n;
};

// Append a fresh aprog to the list with given opcode and label.
fn addprog(a: *asm_, opc: i32, lbl: str) *aprog = {
	let pr: *aprog = alloc(aprog { as_ = opc, line = a.line, label = lbl })!;
	pr.from = alloc(aoperand { })!;
	pr.to   = alloc(aoperand { })!;
	if (a.head == nil) { a.head = pr; }
	else { a.tail.link = pr; };
	a.tail = pr;
	return pr;
};

export fn parse(a: *asm_) i32 = {
	let pending: str;
	pending.ptr = nil; pending.len = 0;

	for (true) {
		let line: *u8;
		let n: u64;
		line, n = nextline(a);
		if (line == nil) { return a.errs; };

		// skip leading ws
		let i: u64 = skipws(line, 0u64, n);
		// blank or //-comment
		if (i >= n) { a.line += 1; continue; };
		if (i + 1u64 < n) {
			if (line[i] == '/') { if (line[i + 1u64] == '/') {
				a.line += 1; continue;
			};};
		};

		// Label? IDENT: starting at column 0 (no leading tab).
		// Only if the identifier is followed by ':'. Otherwise, fall
		// through to mnemonic parsing so e.g. `TEXT foo,$0` (which
		// also starts with an idchar in column 0) gets parsed.
		if (line[0u64] != '\t') {
			if (isidstart(line[i]: i32)) {
				let q: u64 = i;
				let scanid: bool = true;
				for (scanid) {
					if (q >= n) { scanid = false; }
					else { if (isidcont(line[q]: i32)) { q += 1u64; }
					else { scanid = false; }; };
				};
				if (q < n) { if (line[q] == ':') {
					let nm: str = dupstr(line + i, q - i);
					// Pending label gets a NOP prog so addresses pin.
					if (pending.len > 0) {
						let np: *aprog = addprog(a, A_NOP, pending);
					};
					pending = nm;
					a.line += 1;
					continue;
				};};
				// not a label — fall through to mnemonic parse
			};
		};

		// MNEMONIC at the start of the rest. Scan to first ws/EOL.
		let mstart: u64 = i;
		let m: u64 = mstart;
		let scan: bool = true;
		for (scan) {
			if (m >= n)            { scan = false; }
			else { if (line[m] == ' ') { scan = false; }
			else { if (line[m] == '\t')  { scan = false; }
			else { m += 1u64; }; }; };
		};
		let mlen: u64 = m - mstart;
		let opc: i32 = opcodelookup(line + mstart, mlen);
		if (opc == 0) {
			if (mlen > 0u64) {
				perr(a, "unknown opcode");
			};
			pending.ptr = nil; pending.len = 0;
			a.line += 1; continue;
		};

		let pr: *aprog = addprog(a, opc, pending);
		pending.ptr = nil; pending.len = 0;

		// Skip ws after mnemonic
		let r0: u64 = skipws(line, m, n);

		if (opc == A_TEXT) {
			// TEXT name,$framesize — find first ',' as the end of name.
			let q: u64 = r0;
			let commapos: u64 = n;
			let scant: bool = true;
			for (scant) {
				if (q >= n) { scant = false; }
				else { if (line[q] == ',') { commapos = q; scant = false; }
				else { q += 1u64; }; };
			};
			let toop: *aoperand = pr.to;
			toop.atype = D_EXTERN;
			toop.asym = dupstr(line + r0, commapos - r0);
			if (commapos < n) {
				let p2: u64 = commapos + 1u64;
				p2 = skipws(line, p2, n);
				if (p2 < n) { if (line[p2] == '$') { p2 += 1u64; }; };
				let v: i64;
				let used: u64;
				v, used = parsenum(line + p2, n - p2);
				let fromop: *aoperand = pr.from;
				fromop.atype = D_CONST;
				fromop.offset = v;
			};
			a.line += 1; continue;
		};

		if (opc == A_DATA || opc == A_DATAW) {
			// DATA / DATAW name(SB),"escaped bytes" — same syntax,
			// different destination section (.text vs .data).
			let q: u64 = r0;
			let lparen: u64 = n;
			let scand: bool = true;
			for (scand) {
				if (q >= n) { scand = false; }
				else { if (line[q] == '(') { lparen = q; scand = false; }
				else { q += 1u64; }; };
			};
			let toop: *aoperand = pr.to;
			toop.atype = D_EXTERN;
			toop.asym = dupstr(line + r0, lparen - r0);
			// Skip past `(SB)` to land just after ')'.
			let p2: u64 = lparen;
			let scand2: bool = true;
			for (scand2) {
				if (p2 >= n) { scand2 = false; }
				else { if (line[p2] == ')') { p2 += 1u64; scand2 = false; }
				else { p2 += 1u64; }; };
			};
			// Skip ws / ',' / tab between `)` and the `"`.
			let scand3: bool = true;
			for (scand3) {
				if (p2 >= n) { scand3 = false; }
				else { if (line[p2] == ' ') { p2 += 1u64; }
				else { if (line[p2] == ',') { p2 += 1u64; }
				else { if (line[p2] == '\t')  { p2 += 1u64; }
				else { scand3 = false; }; }; }; };
			};
			if (p2 >= n) { perr(a, "DATA missing payload"); a.line += 1; continue; };
			if (line[p2] != '"') { perr(a, "DATA expects \"...\""); a.line += 1; continue; };
			p2 += 1u64;	// past opening "
			// Parse escape sequence into a fresh growable buffer.
			let cap: u64 = 32u64;
			let blen: u64 = 0u64;
			let dbuf: []u8 = alloc([], cap)!;
			for (p2 < n) {
				if (line[p2] == '"') { p2 = p2; p2 += 0u64; p2 = n + 1u64; }
				else {
					let ch: u8 = line[p2];
					p2 += 1u64;
					if (ch == '\\') {
						if (p2 < n) {
							let e: u8 = line[p2];
							p2 += 1u64;
							if (e == 'n') { ch = '\n'; }
							else { if (e == 't') { ch = '\t'; }
							else { if (e == 'r') { ch = '\r'; }
							else { if (e == '\\')  { ch = '\\'; }
							else { if (e == '"')  { ch = '"'; }
							else { if (e == '0')  { ch = '\0'; }
							else { if (e == 'x') {
								if (p2 + 1u64 < n) {
									let hi: u8 = line[p2];
									let lo: u8 = line[p2 + 1u64];
									p2 += 2u64;
									let h: u8 = 0u8;
									let l: u8 = 0u8;
									if (hi <= 57u8) { h = hi - 48u8; }
									else { h = (hi | 32u8) - 97u8 + 10u8; };
									if (lo <= 57u8) { l = lo - 48u8; }
									else { l = (lo | 32u8) - 97u8 + 10u8; };
									ch = (h << 4u8) | l;
								};
							}
							else { ch = e; };};};};};};};
						};
					};
					if (blen + 1u64 > cap) {
						let ncap: u64 = cap * 2u64;
						let nb: []u8 = alloc([], ncap)!;
						let bi: u64 = 0u64;
						for (bi < blen) { nb[bi] = dbuf[bi]; bi += 1u64; };
						dbuf = nb;
						cap = ncap;
					};
					dbuf[blen] = ch;
					blen += 1u64;
				};
			};
			pr.bytes = dbuf.ptr;
			pr.nbytes = blen;
			a.line += 1; continue;
		};

		// Generic instruction: 0/1/2 operands separated by ','.
		// Find top-level comma.
		let comma: i64 = -1i64;
		let q: u64 = r0;
		for (q < n) {
			if (line[q] == ',') {
				if (comma < 0i64) { comma = q: i64; };
			};
			q += 1u64;
		};
		if (comma >= 0i64) {
			let cu: u64 = comma: u64;
			parseoperand(a, line, r0, cu, pr.from);
			parseoperand(a, line + (cu + 1u64), 0u64, n - (cu + 1u64), pr.to);
		} else { if (r0 < n) {
			parseoperand(a, line, r0, n, pr.to);
		};};

		a.line += 1;
	};
	return a.errs;
};

// selfhost/cmd/w6a/asm.ww — port of cmd/w6a/asm.c.
//
// Encode the parsed aprog list into amd64 machine bytes, appending to
// asm_.text. Relocations for CALL/branch targets that resolve to
// externals are queued in asm_.relocs.
//
// Encoding subset matches what w6c emits — see cmd/w6a/asm.c for the
// authoritative list. Helpers (rcode/rhi/modrm/emitrex etc.) are
// fully ported; encode itself is still a stub pending the full
// switch over A_*.

package w6a;

import os;
import rt;
import opcodes;
import strings;

// ---- text buffer growth ------------------------------------------------

export fn emitbyte(a: *asm_, b: u8) void = {
	if (a.textlen + 1u64 > a.textcap) {
		let nc: u64 = a.textcap;
		if (nc == 0u64) { nc = 4096u64; };
		nc = nc * 2u64;
		let nb: []u8 = alloc([], nc)!;
		let i: u64 = 0u64;
		for (i < a.textlen) { nb[i] = a.text[i]; i += 1u64; };
		a.text = nb.ptr;
		a.textcap = nc;
	};
	a.text[a.textlen] = b;
	a.textlen += 1u64;
};

export fn emitu32(a: *asm_, v: u32) void = {
	emitbyte(a, (v & 255u32): u8);
	emitbyte(a, ((v >> 8u32) & 255u32): u8);
	emitbyte(a, ((v >> 16u32) & 255u32): u8);
	emitbyte(a, ((v >> 24u32) & 255u32): u8);
};

export fn addreloc(a: *asm_, off: u64, kind: i32, s: *asym, add: i64) void = {
	let r: *areloc = alloc(areloc { off = off, section = 0, kind = kind, asy = s, addend = add, rnext = a.relocs })!;
	a.relocs = r;
};

// Record a relocation that lives in the .data section. Used by
// DATAR to patch a 64-bit slot with a symbol's runtime VA. obj.ww
// separates these into .rela.data when emitting the .o.
export fn addrelocdata(a: *asm_, off: u64, kind: i32, s: *asym, add: i64) void = {
	let r: *areloc = alloc(areloc { off = off, section = 1, kind = kind, asy = s, addend = add, rnext = a.relocs })!;
	a.relocs = r;
};

// Append one byte to the writable .data buffer. Mirrors emitbyte
// but targets a.data instead of a.text.
export fn emitdatabyte(a: *asm_, b: u8) void = {
	if (a.datalen + 1u64 > a.datacap) {
		let nc: u64 = a.datacap;
		if (nc == 0u64) { nc = 256u64; };
		nc = nc * 2u64;
		let nb: []u8 = alloc([], nc)!;
		let i: u64 = 0u64;
		for (i < a.datalen) { nb[i] = a.data[i]; i += 1u64; };
		a.data = nb.ptr;
		a.datacap = nc;
	};
	a.data[a.datalen] = b;
	a.datalen += 1u64;
};

// ---- register codes ----------------------------------------------------

// Low 3 bits of register encoding.
fn rcode(r: i32) i32 = {
	if (r == D_AX) { return 0; };  if (r == D_CX) { return 1; };
	if (r == D_DX) { return 2; };  if (r == D_BX) { return 3; };
	if (r == D_SP) { return 4; };  if (r == D_BP) { return 5; };
	if (r == D_SI) { return 6; };  if (r == D_DI) { return 7; };
	if (r == D_R8)  { return 0; }; if (r == D_R9)  { return 1; };
	if (r == D_R10) { return 2; }; if (r == D_R11) { return 3; };
	if (r == D_R12) { return 4; }; if (r == D_R13) { return 5; };
	if (r == D_R14) { return 6; }; if (r == D_R15) { return 7; };
	if (r == D_X0) { return 0; };  if (r == D_X1) { return 1; };
	if (r == D_X2) { return 2; };  if (r == D_X3) { return 3; };
	if (r == D_X4) { return 4; };  if (r == D_X5) { return 5; };
	if (r == D_X6) { return 6; };  if (r == D_X7) { return 7; };
	if (r == D_X8)  { return 0; }; if (r == D_X9)  { return 1; };
	if (r == D_X10) { return 2; }; if (r == D_X11) { return 3; };
	if (r == D_X12) { return 4; }; if (r == D_X13) { return 5; };
	if (r == D_X14) { return 6; }; if (r == D_X15) { return 7; };
	return 0;
};

// 1 if r needs the REX high bit (R8..R15 or X8..X15).
fn rhi(r: i32) i32 = {
	if (r >= D_R8) { if (r <= D_R15) { return 1; }; };
	if (r >= D_X8) { if (r <= D_X15) { return 1; }; };
	return 0;
};

fn isxmm(r: i32) bool = {
	if (r >= D_X0) { if (r <= D_X15) { return true; }; };
	return false;
};

// ModR/M byte builder.
fn modrmbyte(mod: i32, reg: i32, rm: i32) u8 = {
	return (((mod & 3) << 6) | ((reg & 7) << 3) | (rm & 7)): u8;
};

// REX prefix; W=1 for 64-bit operand size.
fn emitrex(a: *asm_, regbit: i32, rmbit: i32, w: i32) void = {
	let b: u8 = 64u8;	// 0x40
	if (w != 0)      { b = b | 8u8; };
	if (regbit != 0) { b = b | 4u8; };
	if (rmbit != 0)  { b = b | 1u8; };
	if (b != 64u8) { emitbyte(a, b); }
	else { if (w != 0) { emitbyte(a, b); }; };
};

// ModR/M + (optional) SIB + displacement for [base+disp].
// Special-cases SP (needs SIB) and BP (forces explicit disp).
fn emitmodrmmem(a: *asm_, regfield: i32, base: i32, disp: i64) void = {
	let rm: i32 = rcode(base);
	let needsib: bool = (rm == 4);
	let forceddisp: bool = false;
	if (rm == 5) { if (disp == 0i64) { forceddisp = true; }; };

	let mod: i32 = 2;
	if (disp == 0i64) {
		if (!forceddisp) { mod = 0; }
		else { mod = 1; };
	} else {
		if (disp >= -128i64) { if (disp <= 127i64) { mod = 1; }; };
	};

	emitbyte(a, modrmbyte(mod, regfield, rm));
	if (needsib) {
		emitbyte(a, 36u8);	// 0x24: scale=0 idx=4(none) base=4
	};
	if (mod == 1) {
		emitbyte(a, (disp: u64 & 255u64): u8);
	} else { if (mod == 2) {
		emitu32(a, disp: u32);
	};};
};

// reg→reg "src, dst" generic encoding (89 /r, 01 /r, etc.).
fn encoderr(a: *asm_, opcode: u8, src: i32, dst: i32) void = {
	emitrex(a, rhi(src), rhi(dst), 1);
	emitbyte(a, opcode);
	emitbyte(a, modrmbyte(3, rcode(src), rcode(dst)));
};

// reg→mem(base, disp) (e.g. MOVQ src reg into mem; opcode = 0x89).
fn encoderm(a: *asm_, opcode: u8, srcreg: i32, base: i32, disp: i64) void = {
	emitrex(a, rhi(srcreg), rhi(base), 1);
	emitbyte(a, opcode);
	emitmodrmmem(a, rcode(srcreg), base, disp);
};

// mem(base, disp) → reg (e.g. MOVQ mem into reg; opcode = 0x8B).
fn encodemr(a: *asm_, opcode: u8, dstreg: i32, base: i32, disp: i64) void = {
	emitrex(a, rhi(dstreg), rhi(base), 1);
	emitbyte(a, opcode);
	emitmodrmmem(a, rcode(dstreg), base, disp);
};

// OPCODE /n imm32 reg form (e.g. ADDQ $imm, reg).
fn encoderiimm32(a: *asm_, opcode: u8, subop: i32, dst: i32, imm: i32) void = {
	emitrex(a, 0, rhi(dst), 1);
	emitbyte(a, opcode);
	emitbyte(a, modrmbyte(3, subop, rcode(dst)));
	emitu32(a, imm: u32);
};

// Unary on reg: F7 /n reg, etc.
fn encodeunary(a: *asm_, opcode: u8, subop: i32, dst: i32) void = {
	emitrex(a, 0, rhi(dst), 1);
	emitbyte(a, opcode);
	emitbyte(a, modrmbyte(3, subop, rcode(dst)));
};

// SSE2 helpers. Plan 9 syntax: source first, destination second.
// For ADDSD-style ops we put dst in the reg field, src in r/m.
fn sserr(a: *asm_, prefix: u8, op2: u8, regop: i32, rmop: i32) void = {
	if (prefix != 0u8) { emitbyte(a, prefix); };
	emitrex(a, rhi(regop), rhi(rmop), 0);
	emitbyte(a, 15u8);	// 0x0F
	emitbyte(a, op2);
	emitbyte(a, modrmbyte(3, rcode(regop), rcode(rmop)));
};

fn ssemrload(a: *asm_, prefix: u8, op2: u8, regop: i32, base: i32, disp: i64) void = {
	if (prefix != 0u8) { emitbyte(a, prefix); };
	emitrex(a, rhi(regop), rhi(base), 0);
	emitbyte(a, 15u8);
	emitbyte(a, op2);
	emitmodrmmem(a, rcode(regop), base, disp);
};

// REX.W variant of sse_rr (CVTTSD2SI / CVTSI2SD).
fn sserrw(a: *asm_, prefix: u8, op2: u8, regop: i32, rmop: i32) void = {
	if (prefix != 0u8) { emitbyte(a, prefix); };
	emitrex(a, rhi(regop), rhi(rmop), 1);
	emitbyte(a, 15u8);
	emitbyte(a, op2);
	emitbyte(a, modrmbyte(3, rcode(regop), rcode(rmop)));
};

// ---- label resolution / fixups ----------------------------------------

fn resolvelabel(a: *asm_, name: str) u64 = {
	let s: *asym = a.syms;
	for (s != nil) {
		if (s.defined != 0) { if (strings.compare(s.name, name) == 0) { return s.addr; }; };
		s = s.snext;
	};
	return 0u64;
};

fn labeldefined(a: *asm_, name: str) bool = {
	let s: *asym = a.syms;
	for (s != nil) {
		if (s.defined != 0) { if (strings.compare(s.name, name) == 0) { return true; }; };
		s = s.snext;
	};
	return false;
};

// ---- fixup helper -----------------------------------------------------

fn addfixup(a: *asm_, off: u64, label: str) void = {
	let f: *afixup = alloc(afixup { off = off, label = label, fnext = a.fixups })!;
	a.fixups = f;
};

fn isgpr(t: i32) bool = {
	if (t >= D_AX) { if (t <= D_R15) { return true; }; };
	return false;
};

// `intern` lives in parse.ww — flat-scope concat lets us call it
// directly without an @symbol declaration here.

// ---- encode ----------------------------------------------------------

export fn encode(a: *asm_) i32 = {
	let p: *aprog = a.head;
	for (p != nil) {
		// Define any pending label at the current PC.
		if (p.label.len > 0) {
			let s: *asym = intern(a, p.label);
			s.defined = 1;
			s.istext = 1;
			s.addr = a.textlen;
		};
		let op: i32 = p.as_;

		if (op == A_NOP) {
			p = p.link; continue;
		};
		if (op == A_TEXT) {
			let s: *asym = intern(a, p.to.asym);
			s.defined = 1;
			s.istext = 1;
			s.isglobal = 1;
			s.addr = a.textlen;
			p = p.link; continue;
		};
		if (op == A_DATA) {
			let s: *asym = intern(a, p.to.asym);
			s.defined = 1;
			s.istext = 1;
			s.isglobal = 1;
			s.addr = a.textlen;
			let i: u64 = 0u64;
			for (i < p.nbytes) { emitbyte(a, p.bytes[i]); i += 1u64; };
			p = p.link; continue;
		};
		if (op == A_DATAW) {
			// Writable variant: bytes go into .data instead of
			// .text. obj.ww emits the extra section conditionally
			// on datalen > 0 so .o output stays byte-identical
			// for inputs that don't use DATAW.
			let s: *asym = intern(a, p.to.asym);
			s.defined = 1;
			s.isdata = 1;
			s.isglobal = 1;
			s.addr = a.datalen;
			let i: u64 = 0u64;
			for (i < p.nbytes) { emitdatabyte(a, p.bytes[i]); i += 1u64; };
			p = p.link; continue;
		};
		if (op == A_DATAR) {
			// DATAR slot+off(SB), target(SB) — record an
			// R_X86_64_64 relocation at slot+off in .data
			// pointing at target. Slot must already be defined
			// by a prior DATAW.
			let holder: *asym = intern(a, p.from.asym);
			if (holder.defined == 0) {
				p = p.link; continue;
			};
			if (holder.isdata == 0) {
				p = p.link; continue;
			};
			let target: *asym = intern(a, p.to.asym);
			let reloff: u64 = holder.addr + p.from.offset: u64;
			addrelocdata(a, reloff, 1 /* R_X86_64_64 */,
			    target, 0i64);
			p = p.link; continue;
		};
		if (op == A_RET) {
			emitbyte(a, 195u8);	// 0xC3
			p = p.link; continue;
		};
		if (op == A_SYSCALL) {
			emitbyte(a, 15u8);
			emitbyte(a, 5u8);
			p = p.link; continue;
		};
		if (op == A_PUSHQ) {
			if (rhi(p.to.atype) != 0) { emitbyte(a, 65u8); };	// 0x41
			emitbyte(a, (80 + rcode(p.to.atype)): u8);	// 0x50
			p = p.link; continue;
		};
		if (op == A_POPQ) {
			if (rhi(p.to.atype) != 0) { emitbyte(a, 65u8); };
			emitbyte(a, (88 + rcode(p.to.atype)): u8);	// 0x58
			p = p.link; continue;
		};
		if (op == A_NEGQ)  { encodeunary(a, 247u8, 3, p.to.atype); p = p.link; continue; };
		if (op == A_NOTQ)  { encodeunary(a, 247u8, 2, p.to.atype); p = p.link; continue; };
		if (op == A_IDIVQ) { encodeunary(a, 247u8, 7, p.to.atype); p = p.link; continue; };
		if (op == A_DIVQ)  { encodeunary(a, 247u8, 6, p.to.atype); p = p.link; continue; };
		if (op == A_CQO) {
			emitbyte(a, 72u8);	// REX.W (0x48)
			emitbyte(a, 153u8);	// 0x99
			p = p.link; continue;
		};

		if (op == A_MOVQ) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_CONST) { if (isgpr(tt)) {
				let v: i64 = p.from.offset;
				if (v >= -2147483648i64) { if (v <= 2147483647i64) {
					encoderiimm32(a, 199u8, 0, tt, v: i32);
					p = p.link; continue;
				};};
				// movabs r64, imm64: REX.W B8+rd imm64
				emitrex(a, 0, rhi(tt), 1);
				emitbyte(a, (184 + rcode(tt)): u8);
				let k: i32 = 0;
				for (k < 8) {
					emitbyte(a, ((v: u64 >> (k: u64 * 8u64)) & 255u64): u8);
					k += 1;
				};
				p = p.link; continue;
			};};
			if (isgpr(ft)) { if (isgpr(tt)) {
				encoderr(a, 137u8, ft, tt);	// 0x89
				p = p.link; continue;
			};};
			if (ft == D_INDIR) { if (isgpr(tt)) {
				encodemr(a, 139u8, tt, p.from.reg, p.from.offset);	// 0x8B
				p = p.link; continue;
			};};
			if (isgpr(ft)) { if (tt == D_INDIR) {
				encoderm(a, 137u8, ft, p.to.reg, p.to.offset);
				p = p.link; continue;
			};};
			if (ft == D_CONST) { if (tt == D_INDIR) {
				emitrex(a, 0, rhi(p.to.reg), 1);
				emitbyte(a, 199u8);
				emitmodrmmem(a, 0, p.to.reg, p.to.offset);
				emitu32(a, p.from.offset: u32);
				p = p.link; continue;
			};};
			if (ft == D_EXTERN) { if (isgpr(tt)) {
				// RIP-relative load: 48 8B /r mod=00 rm=5 disp32
				emitrex(a, rhi(tt), 0, 1);
				emitbyte(a, 139u8);
				emitbyte(a, modrmbyte(0, rcode(tt), 5));
				let reloff: u64 = a.textlen;
				emitu32(a, 0u32);
				let s: *asym = intern(a, p.from.asym);
				addreloc(a, reloff, 2, s, -4i64);
				p = p.link; continue;
			};};
			if (isgpr(ft)) { if (tt == D_EXTERN) {
				// RIP-relative store: 48 89 /r mod=00 rm=5 disp32
				emitrex(a, rhi(ft), 0, 1);
				emitbyte(a, 137u8);
				emitbyte(a, modrmbyte(0, rcode(ft), 5));
				let reloff: u64 = a.textlen;
				emitu32(a, 0u32);
				let s: *asym = intern(a, p.to.asym);
				addreloc(a, reloff, 2, s, -4i64);
				p = p.link; continue;
			};};
			os.write(2, "w6a: unsupported MOVQ shape\n".ptr, 27u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_MOVB) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (isgpr(ft)) { if (tt == D_INDIR) {
				emitrex(a, rhi(ft), rhi(p.to.reg), 0);
				emitbyte(a, 136u8);	// 0x88
				emitmodrmmem(a, rcode(ft), p.to.reg, p.to.offset);
				p = p.link; continue;
			};};
			if (ft == D_INDIR) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), rhi(p.from.reg), 0);
				emitbyte(a, 138u8);	// 0x8A
				emitmodrmmem(a, rcode(tt), p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			os.write(2, "w6a: unsupported MOVB shape\n".ptr, 27u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_MOVW) {
			// 16-bit MOV: 0x66 operand-size prefix + the 32-bit
			// MOV opcodes 0x89 / 0x8B. No REX.W.
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (isgpr(ft)) { if (tt == D_INDIR) {
				emitbyte(a, 102u8);	// 0x66
				emitrex(a, rhi(ft), rhi(p.to.reg), 0);
				emitbyte(a, 137u8);	// 0x89
				emitmodrmmem(a, rcode(ft), p.to.reg, p.to.offset);
				p = p.link; continue;
			};};
			if (ft == D_INDIR) { if (isgpr(tt)) {
				emitbyte(a, 102u8);	// 0x66
				emitrex(a, rhi(tt), rhi(p.from.reg), 0);
				emitbyte(a, 139u8);	// 0x8B
				emitmodrmmem(a, rcode(tt), p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			os.write(2, "w6a: unsupported MOVW shape\n".ptr, 27u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_MOVZWQ) {
			// MOVZX r64, r/m16 — 0F B7 /r with REX.W.
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_INDIR) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), rhi(p.from.reg), 1);
				emitbyte(a, 15u8);
				emitbyte(a, 183u8);	// 0xB7
				emitmodrmmem(a, rcode(tt), p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			os.write(2, "w6a: unsupported MOVZWQ shape\n".ptr, 29u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_MOVSWQ) {
			// MOVSX r64, r/m16 — 0F BF /r with REX.W.
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_INDIR) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), rhi(p.from.reg), 1);
				emitbyte(a, 15u8);
				emitbyte(a, 191u8);	// 0xBF
				emitmodrmmem(a, rcode(tt), p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			if (isgpr(ft)) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), rhi(ft), 1);
				emitbyte(a, 15u8);
				emitbyte(a, 191u8);	// 0xBF
				emitbyte(a, modrmbyte(3, rcode(tt), rcode(ft)));
				p = p.link; continue;
			};};
			os.write(2, "w6a: unsupported MOVSWQ shape\n".ptr, 29u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_MOVSBQ) {
			// MOVSX r64, r/m8 — 0F BE /r with REX.W.
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_INDIR) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), rhi(p.from.reg), 1);
				emitbyte(a, 15u8);
				emitbyte(a, 190u8);	// 0xBE
				emitmodrmmem(a, rcode(tt), p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			if (isgpr(ft)) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), rhi(ft), 1);
				emitbyte(a, 15u8);
				emitbyte(a, 190u8);	// 0xBE
				emitbyte(a, modrmbyte(3, rcode(tt), rcode(ft)));
				p = p.link; continue;
			};};
			os.write(2, "w6a: unsupported MOVSBQ shape\n".ptr, 29u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_MOVZBQ) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_INDIR) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), rhi(p.from.reg), 1);
				emitbyte(a, 15u8);
				emitbyte(a, 182u8);	// 0xB6
				emitmodrmmem(a, rcode(tt), p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			os.write(2, "w6a: unsupported MOVZBQ shape\n".ptr, 29u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_MOVL) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (isgpr(ft)) { if (tt == D_INDIR) {
				emitrex(a, rhi(ft), rhi(p.to.reg), 0);
				emitbyte(a, 137u8);
				emitmodrmmem(a, rcode(ft), p.to.reg, p.to.offset);
				p = p.link; continue;
			};};
			if (ft == D_INDIR) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), rhi(p.from.reg), 0);
				emitbyte(a, 139u8);
				emitmodrmmem(a, rcode(tt), p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			if (isgpr(ft)) { if (isgpr(tt)) {
				emitrex(a, rhi(ft), rhi(tt), 0);
				emitbyte(a, 137u8);
				emitbyte(a, modrmbyte(3, rcode(ft), rcode(tt)));
				p = p.link; continue;
			};};
			os.write(2, "w6a: unsupported MOVL shape\n".ptr, 27u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_MOVSXD) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_INDIR) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), rhi(p.from.reg), 1);
				emitbyte(a, 99u8);	// 0x63
				emitmodrmmem(a, rcode(tt), p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			if (isgpr(ft)) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), rhi(ft), 1);
				emitbyte(a, 99u8);	// 0x63
				emitbyte(a, modrmbyte(3, rcode(tt), rcode(ft)));
				p = p.link; continue;
			};};
			os.write(2, "w6a: unsupported MOVSXD shape\n".ptr, 29u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_MOVSD) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (isxmm(ft)) { if (isxmm(tt)) {
				sserr(a, 242u8, 16u8, tt, ft);
				p = p.link; continue;
			};};
			if (ft == D_INDIR) { if (isxmm(tt)) {
				ssemrload(a, 242u8, 16u8, tt, p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			if (isxmm(ft)) { if (tt == D_INDIR) {
				ssemrload(a, 242u8, 17u8, ft, p.to.reg, p.to.offset);
				p = p.link; continue;
			};};
			os.write(2, "w6a: unsupported MOVSD shape\n".ptr, 28u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_ADDSD) { sserr(a, 242u8, 88u8,  p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_SUBSD) { sserr(a, 242u8, 92u8,  p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_MULSD) { sserr(a, 242u8, 89u8,  p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_DIVSD) { sserr(a, 242u8, 94u8,  p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_UCOMISD)   { sserr(a, 102u8, 46u8, p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_CVTTSD2SI) { sserrw(a, 242u8, 44u8, p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_CVTSI2SD)  { sserrw(a, 242u8, 42u8, p.to.atype, p.from.atype); p = p.link; continue; };

		if (op == A_MOVSS) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (isxmm(ft)) { if (isxmm(tt)) {
				sserr(a, 243u8, 16u8, tt, ft); p = p.link; continue;
			};};
			if (ft == D_INDIR) { if (isxmm(tt)) {
				ssemrload(a, 243u8, 16u8, tt, p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			if (isxmm(ft)) { if (tt == D_INDIR) {
				ssemrload(a, 243u8, 17u8, ft, p.to.reg, p.to.offset);
				p = p.link; continue;
			};};
			os.write(2, "w6a: unsupported MOVSS shape\n".ptr, 28u64);
			a.errs += 1;
			p = p.link; continue;
		};

		if (op == A_ADDSS) { sserr(a, 243u8, 88u8, p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_SUBSS) { sserr(a, 243u8, 92u8, p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_MULSS) { sserr(a, 243u8, 89u8, p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_DIVSS) { sserr(a, 243u8, 94u8, p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_UCOMISS)   { sserr(a, 0u8,   46u8, p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_CVTTSS2SI) { sserrw(a, 243u8, 44u8, p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_CVTSI2SS)  { sserrw(a, 243u8, 42u8, p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_CVTSD2SS)  { sserr(a, 242u8, 90u8, p.to.atype, p.from.atype); p = p.link; continue; };
		if (op == A_CVTSS2SD)  { sserr(a, 243u8, 90u8, p.to.atype, p.from.atype); p = p.link; continue; };

		if (op == A_ADDQ) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_CONST) { if (isgpr(tt)) {
				encoderiimm32(a, 129u8, 0, tt, p.from.offset: i32);	// 0x81
				p = p.link; continue;
			};};
			if (ft == D_CONST) { if (tt == D_INDIR) {
				emitrex(a, 0, rhi(p.to.reg), 1);
				emitbyte(a, 129u8);
				emitmodrmmem(a, 0, p.to.reg, p.to.offset);
				emitu32(a, p.from.offset: u32);
				p = p.link; continue;
			};};
			if (isgpr(ft)) { if (tt == D_INDIR) {
				encoderm(a, 1u8, ft, p.to.reg, p.to.offset);
				p = p.link; continue;
			};};
			if (ft == D_INDIR) { if (isgpr(tt)) {
				encodemr(a, 3u8, tt, p.from.reg, p.from.offset);
				p = p.link; continue;
			};};
			encoderr(a, 1u8, ft, tt);
			p = p.link; continue;
		};

		if (op == A_SUBQ) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_CONST) { if (isgpr(tt)) {
				encoderiimm32(a, 129u8, 5, tt, p.from.offset: i32);
				p = p.link; continue;
			};};
			if (ft == D_CONST) { if (tt == D_INDIR) {
				emitrex(a, 0, rhi(p.to.reg), 1);
				emitbyte(a, 129u8);
				emitmodrmmem(a, 5, p.to.reg, p.to.offset);
				emitu32(a, p.from.offset: u32);
				p = p.link; continue;
			};};
			if (isgpr(ft)) { if (tt == D_INDIR) {
				encoderm(a, 41u8, ft, p.to.reg, p.to.offset);	// 0x29
				p = p.link; continue;
			};};
			if (ft == D_INDIR) { if (isgpr(tt)) {
				encodemr(a, 43u8, tt, p.from.reg, p.from.offset);	// 0x2B
				p = p.link; continue;
			};};
			encoderr(a, 41u8, ft, tt);
			p = p.link; continue;
		};

		if (op == A_ANDQ) {
			// AND r/m64, imm32 — 0x81 /4 (REX.W). Without the
			// D_CONST path encoderr would silently emit 0x21
			// with garbage reg fields.
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_CONST) { if (isgpr(tt)) {
				encoderiimm32(a, 129u8, 4, tt, p.from.offset: i32);
				p = p.link; continue;
			};};
			encoderr(a, 33u8, ft, tt);	// 0x21
			p = p.link; continue;
		};
		if (op == A_ORQ) {
			// OR r/m64, imm32 — 0x81 /1 (REX.W). Mirrors ANDQ.
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_CONST) { if (isgpr(tt)) {
				encoderiimm32(a, 129u8, 1, tt, p.from.offset: i32);
				p = p.link; continue;
			};};
			encoderr(a, 9u8, ft, tt);	// 0x09
			p = p.link; continue;
		};
		if (op == A_XORQ) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_CONST) { if (isgpr(tt)) {
				encoderiimm32(a, 129u8, 6, tt, p.from.offset: i32);
				p = p.link; continue;
			};};
			encoderr(a, 49u8, ft, tt);	// 0x31
			p = p.link; continue;
		};
		if (op == A_IMULQ) {
			emitrex(a, rhi(p.to.atype), rhi(p.from.atype), 1);
			emitbyte(a, 15u8);
			emitbyte(a, 175u8);	// 0xAF
			emitbyte(a, modrmbyte(3, rcode(p.to.atype), rcode(p.from.atype)));
			p = p.link; continue;
		};
		if (op == A_SHLQ) { encodeunary(a, 211u8, 4, p.to.atype); p = p.link; continue; };	// 0xD3
		if (op == A_SHRQ) { encodeunary(a, 211u8, 5, p.to.atype); p = p.link; continue; };
		// #136: SAR r/m64, CL — REX.W + D3 /7 (arithmetic right
		// shift, sign-extends MSB; cstage twin cmd/w6a/asm.c).
		if (op == A_SARQ) { encodeunary(a, 211u8, 7, p.to.atype); p = p.link; continue; };
		if (op == A_CMPQ) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_CONST) { if (isgpr(tt)) {
				encoderiimm32(a, 129u8, 7, tt, p.from.offset: i32);
				p = p.link; continue;
			};};
			encoderr(a, 57u8, ft, tt);	// 0x39
			p = p.link; continue;
		};

		if (op == A_LEAQ) {
			let ft: i32 = p.from.atype;
			let tt: i32 = p.to.atype;
			if (ft == D_INDIR) { if (isgpr(tt)) {
				encodemr(a, 141u8, tt, p.from.reg, p.from.offset);	// 0x8D
				p = p.link; continue;
			};};
			if (ft == D_EXTERN) { if (isgpr(tt)) {
				emitrex(a, rhi(tt), 0, 1);
				emitbyte(a, 141u8);
				emitbyte(a, modrmbyte(0, rcode(tt), 5));
				let reloff: u64 = a.textlen;
				emitu32(a, 0u32);
				let s: *asym = intern(a, p.from.asym);
				addreloc(a, reloff, 2, s, -4i64);
				p = p.link; continue;
			};};
			p = p.link; continue;
		};

		if (op == A_CALL) {
			let tt: i32 = p.to.atype;
			if (tt == D_EXTERN) {
				emitbyte(a, 232u8);	// 0xE8
				let reloff: u64 = a.textlen;
				emitu32(a, 0u32);
				let s: *asym = intern(a, p.to.asym);
				addreloc(a, reloff, 4, s, -4i64);
				p = p.link; continue;
			};
			if (tt == D_BRANCH) {
				emitbyte(a, 232u8);
				addfixup(a, a.textlen, p.to.asym);
				emitu32(a, 0u32);
				p = p.link; continue;
			};
			if (isgpr(tt)) {
				if (rhi(tt) != 0) { emitbyte(a, 65u8); };
				emitbyte(a, 255u8);	// 0xFF
				emitbyte(a, modrmbyte(3, 2, rcode(tt)));
				p = p.link; continue;
			};
			p = p.link; continue;
		};

		if (op == A_JMP) {
			emitbyte(a, 233u8);	// 0xE9
			addfixup(a, a.textlen, p.to.asym);
			emitu32(a, 0u32);
			p = p.link; continue;
		};

		// Conditional jumps. 0x0F + cc + rel32.
		let cc: u8 = 0u8;
		let isjcc: bool = true;
		switch (op) {
		case A_JE:  cc = 132u8;	// 0x84
		case A_JZ:  cc = 132u8;
		case A_JNE: cc = 133u8;
		case A_JNZ: cc = 133u8;
		case A_JL:  cc = 140u8;
		case A_JLE: cc = 142u8;
		case A_JG:  cc = 143u8;
		case A_JGE: cc = 141u8;
		case A_JB:  cc = 130u8;
		case A_JBE: cc = 134u8;
		case A_JA:  cc = 135u8;
		case A_JAE: cc = 131u8;
		case A_JP:  cc = 138u8;	// 0x8A, UCOMISD unordered (#97)
		case:       isjcc = false;
		};
		if (isjcc) {
			emitbyte(a, 15u8);
			emitbyte(a, cc);
			addfixup(a, a.textlen, p.to.asym);
			emitu32(a, 0u32);
			p = p.link; continue;
		};

		os.write(2, "w6a: unsupported opcode\n".ptr, 23u64);
		a.errs += 1;
		p = p.link;
	};

	// Second pass: patch fixups (forward label refs).
	let f: *afixup = a.fixups;
	for (f != nil) {
		if (!labeldefined(a, f.label)) {
			os.write(2, "w6a: undefined label '".ptr, 21u64);
			let lbl: str = f.label;
			os.write(2, lbl.ptr, lbl.len: u64);
			os.write(2, "'\n".ptr, 2u64);
			a.errs += 1;
			f = f.fnext;
			continue;
		};
		let target: u64 = resolvelabel(a, f.label);
		let rel: i64 = target: i64 - (f.off: i64 + 4i64);
		let rel32: u32 = rel: u32;
		a.text[f.off]         = (rel32 & 255u32): u8;
		a.text[f.off + 1u64]  = ((rel32 >> 8u32)  & 255u32): u8;
		a.text[f.off + 2u64]  = ((rel32 >> 16u32) & 255u32): u8;
		a.text[f.off + 3u64]  = ((rel32 >> 24u32) & 255u32): u8;
		f = f.fnext;
	};
	return a.errs;
};

// selfhost/cmd/w6a/obj.ww — port of cmd/w6a/obj.c.
//
// Emit a tiny ELF64 relocatable object. Layout (in file order):
//   [0] ELF header
//   [1] Section .text (program bytes)
//   [2] Section .rela.text (relocations)
//   [3] Section .symtab
//   [4] Section .strtab
//   [5] Section .shstrtab
//   [6] Section header table
//
// Symtab indices: 0 = STN_UNDEF, 1.. = our syms. Only GLOBAL symbols.

package w6a;

import os;
import opcodes;

// Local wrappers around os.writeall's tagged return — collapse the
// (i64 | oserror) back to a boolean / int sentinel for the
// length-checked / fire-and-forget write patterns below.
fn wrn(fd: i32, p: *u8, n: u64, want: i64) bool = {
	let r: (i64 | os.oserror) = os.writeall(fd, p, n);
	match (r) {
	case let v: i64 => return v == want;
	case let e: os.oserror => return false;
	};
	return false;
};

fn wrdrop(fd: i32, p: *u8, n: u64) void = {
	let r: (i64 | os.oserror) = os.writeall(fd, p, n);
	match (r) {
	case let v: i64 => { };
	case let e: os.oserror => { };
	};
};

// ---- ELF constants ----------------------------------------------------
def ELFCLASS64:   u8  = 2u8;
def ELFDATA2LSB:  u8  = 1u8;
def EV_CURRENT_W: u32 = 1u32;
def ET_REL_W:     u16 = 1u16;
def EM_X86_64_W:  u16 = 62u16;

def SHT_NULL_C:     u32 = 0u32;
def SHT_PROGBITS_C: u32 = 1u32;
def SHT_SYMTAB_C:   u32 = 2u32;
def SHT_STRTAB_C:   u32 = 3u32;
def SHT_RELA_C:     u32 = 4u32;

def SHF_WRITE:      u64 = 1u64;
def SHF_ALLOC:      u64 = 2u64;
def SHF_EXECINSTR:  u64 = 4u64;
def SHF_INFO_LINK:  u64 = 64u64;	// 0x40

def STB_GLOBAL:     u8 = 1u8;
def STT_NOTYPE:     u8 = 0u8;
def STT_OBJECT:     u8 = 1u8;
def STT_FUNC:       u8 = 2u8;

// Sizes of fixed structures.
def EHDR_SZ: u64 = 64u64;
def SHDR_SZ: u64 = 64u64;
def SYM_SZ:  u64 = 24u64;
def RELA_SZ: u64 = 24u64;

// ---- LE byte writers (own the bytes — write into a *u8 + offset) ----

fn wru8(p: *u8, off: u64, v: u8) void = { p[off] = v; };
fn wru16(p: *u8, off: u64, v: u16) void = {
	p[off]        = (v & 255u16): u8;
	p[off + 1u64] = ((v >> 8u16) & 255u16): u8;
};
fn wru32(p: *u8, off: u64, v: u32) void = {
	p[off]        = (v & 255u32): u8;
	p[off + 1u64] = ((v >> 8u32)  & 255u32): u8;
	p[off + 2u64] = ((v >> 16u32) & 255u32): u8;
	p[off + 3u64] = ((v >> 24u32) & 255u32): u8;
};
fn wru64(p: *u8, off: u64, v: u64) void = {
	wru32(p, off,        (v & 4294967295u64): u32);
	wru32(p, off + 4u64, ((v >> 32u64) & 4294967295u64): u32);
};

// ---- growable byte buffer ---------------------------------------------

type buf = struct {
	p:    *u8,
	n:    u64,
	cap:  u64,
};

fn bufinit(b: *buf) void = {
	b.cap = 256u64;
	b.n = 0u64;
	let np: []u8 = alloc([], b.cap)!;
	b.p = np.ptr;
};

fn bufgrow(b: *buf, need: u64) void = {
	if (b.n + need <= b.cap) { return; };
	let nc: u64 = b.cap;
	for (nc < b.n + need) { nc = nc * 2u64; };
	let np: []u8 = alloc([], nc)!;
	let i: u64 = 0u64;
	for (i < b.n) { np[i] = b.p[i]; i += 1u64; };
	b.p = np.ptr;
	b.cap = nc;
};

fn bufputb(b: *buf, src: *u8, n: u64) void = {
	bufgrow(b, n);
	let i: u64 = 0u64;
	for (i < n) { b.p[b.n + i] = src[i]; i += 1u64; };
	b.n += n;
};

// Write a NUL-terminated C-string copy of `s` into b. Returns offset
// where it started (suitable for st_name / sh_name fields).
fn bufputcstr(b: *buf, s: str) u32 = {
	let off: u32 = b.n: u32;
	bufgrow(b, s.len: u64 + 1u64);
	let i: i32 = 0;
	for (i < s.len) { b.p[b.n] = s[i]; b.n += 1u64; i += 1; };
	b.p[b.n] = 0u8;
	b.n += 1u64;
	return off;
};

// ---- emitelf ---------------------------------------------------------

export fn emitelf(a: *asm_, fd: i32) i32 = {
	let shstr: buf;  bufinit(&shstr);
	let str_:  buf;  bufinit(&str_);
	let sym:   buf;  bufinit(&sym);
	let rela:  buf;  bufinit(&rela);
	let relad: buf;  bufinit(&relad);

	// Index 0 = empty.
	let zero: u8 = 0u8;
	bufputb(&shstr, &zero, 1u64);
	bufputb(&str_,  &zero, 1u64);

	let hasdata: bool = a.datalen > 0u64;
	let hasdatarelocs: bool = false;
	let rscan: *areloc = a.relocs;
	for (rscan != nil) {
		if (rscan.section == 1) { hasdatarelocs = true; };
		rscan = rscan.rnext;
	};

	// Section indices (mirror cmd/w6a/obj.c):
	//   without data, without data-relocs:
	//     1=.text 2=.rela.text 3=.symtab 4=.strtab 5=.shstrtab
	//   with data, no data-relocs:
	//     1=.text 2=.rela.text 3=.data 4=.symtab 5=.strtab 6=.shstrtab
	//   with data + data-relocs:
	//     1=.text 2=.rela.text 3=.data 4=.rela.data 5=.symtab
	//     6=.strtab 7=.shstrtab
	let SH_TEXT:   u16 = 1u16;
	let SH_DATA:   u16 = 0u16;
	let SH_RELAD:  u16 = 0u16;
	let SH_SYMTAB: u16 = 3u16;
	if (hasdata) {
		SH_DATA = 3u16;
		if (hasdatarelocs) {
			SH_RELAD = 4u16;
			SH_SYMTAB = 5u16;
		} else {
			SH_SYMTAB = 4u16;
		};
	};
	let SH_STRTAB: u16 = SH_SYMTAB + 1u16;
	let SH_SHSTR:  u16 = SH_STRTAB + 1u16;

	// Section name offsets. Append .data / .rela.data only when
	// used so the .shstrtab buffer stays byte-identical for the
	// no-DATAW case (test 991 byte-diff invariant).
	let shntext:     u32 = bufputcstr(&shstr, ".text");
	let shnrela:     u32 = bufputcstr(&shstr, ".rela.text");
	let shndata:     u32 = 0u32;
	let shnrelad:    u32 = 0u32;
	if (hasdata) { shndata = bufputcstr(&shstr, ".data"); };
	if (hasdata) { if (hasdatarelocs) {
		shnrelad = bufputcstr(&shstr, ".rela.data");
	};};
	let shnsymtab:   u32 = bufputcstr(&shstr, ".symtab");
	let shnstrtab:   u32 = bufputcstr(&shstr, ".strtab");
	let shnshstrtab: u32 = bufputcstr(&shstr, ".shstrtab");

	// Symbol 0 — STN_UNDEF (24 zero bytes).
	let zsym: [24]u8;
	let zi: i32 = 0;
	for (zi < 24) { zsym[zi] = 0u8; zi += 1; };
	bufputb(&sym, zsym.ptr, 24u64);

	// Build symbols.
	let idx: i32 = 1;
	let s: *asym = a.syms;
	for (s != nil) {
		let entry: [24]u8;
		let ei: i32 = 0;
		for (ei < 24) { entry[ei] = 0u8; ei += 1; };
		let stname: u32 = bufputcstr(&str_, s.name);
		wru32(entry.ptr, 0u64, stname);
		if (s.defined != 0) {
			if (s.isdata != 0) {
				wru8(entry.ptr,  4u64, ((STB_GLOBAL << 4u8) | STT_OBJECT));
				wru16(entry.ptr, 6u64, SH_DATA);
			} else {
				wru8(entry.ptr,  4u64, ((STB_GLOBAL << 4u8) | STT_FUNC));
				wru16(entry.ptr, 6u64, SH_TEXT);
			};
			wru64(entry.ptr, 8u64, s.addr);
		} else {
			wru8(entry.ptr,  4u64, ((STB_GLOBAL << 4u8) | STT_NOTYPE));
			wru16(entry.ptr, 6u64, 0u16);
		};
		bufputb(&sym, entry.ptr, 24u64);
		s.idx = idx;
		idx += 1;
		s = s.snext;
	};

	// Build relocations — split into text vs data buffers.
	let r: *areloc = a.relocs;
	for (r != nil) {
		let entry: [24]u8;
		wru64(entry.ptr,  0u64, r.off);
		let rinfo: u64 = (r.asy.idx: u64 << 32u64) | (r.kind: u64 & 4294967295u64);
		wru64(entry.ptr,  8u64, rinfo);
		wru64(entry.ptr, 16u64, r.addend: u64);
		if (r.section == 1) {
			bufputb(&relad, entry.ptr, 24u64);
		} else {
			bufputb(&rela, entry.ptr, 24u64);
		};
		r = r.rnext;
	};

	// File offsets.
	let off:      u64 = EHDR_SZ;
	let offtext: u64 = off;  off = off + a.textlen;
	let offrela: u64 = off;  off = off + rela.n;
	let offdata: u64 = off;  if (hasdata) { off = off + a.datalen; };
	let offrelad: u64 = off; if (hasdata) { if (hasdatarelocs) {
		off = off + relad.n;
	};};
	let offsym:  u64 = off;  off = off + sym.n;
	let offstr:  u64 = off;  off = off + str_.n;
	let offshstr: u64 = off; off = off + shstr.n;
	for ((off & 7u64) != 0u64) { off += 1u64; };
	let offshdr: u64 = off;
	let NSECT: u16 = 6u16;
	if (hasdata) {
		if (hasdatarelocs) { NSECT = 8u16; }
		else { NSECT = 7u16; };
	};

	// ---- Ehdr ----
	let eh: [64]u8;
	let i: i32 = 0;
	for (i < 64) { eh[i] = 0u8; i += 1; };
	eh[0] = 127u8;	// 0x7f
	eh[1] = 'E';
	eh[2] = 'L';
	eh[3] = 'F';
	eh[4] = ELFCLASS64;
	eh[5] = ELFDATA2LSB;
	eh[6] = EV_CURRENT_W: u8;
	wru16(eh.ptr, 16u64, ET_REL_W);
	wru16(eh.ptr, 18u64, EM_X86_64_W);
	wru32(eh.ptr, 20u64, EV_CURRENT_W);
	wru64(eh.ptr, 24u64, 0u64);		// e_entry
	wru64(eh.ptr, 32u64, 0u64);		// e_phoff
	wru64(eh.ptr, 40u64, offshdr);	// e_shoff
	wru32(eh.ptr, 48u64, 0u32);		// e_flags
	wru16(eh.ptr, 52u64, 64u16);		// e_ehsize
	wru16(eh.ptr, 54u64, 0u16);		// e_phentsize
	wru16(eh.ptr, 56u64, 0u16);		// e_phnum
	wru16(eh.ptr, 58u64, 64u16);		// e_shentsize
	wru16(eh.ptr, 60u64, NSECT);		// e_shnum
	wru16(eh.ptr, 62u64, SH_SHSTR);	// e_shstrndx

	if (!wrn(fd, eh.ptr, 64u64, 64i64)) { return -1; };
	if (a.textlen > 0u64) {
		if (!wrn(fd, a.text, a.textlen, a.textlen: i64)) { return -1; };
	};
	if (rela.n > 0u64) {
		if (!wrn(fd, rela.p, rela.n, rela.n: i64)) { return -1; };
	};
	if (hasdata) {
		if (a.datalen > 0u64) {
			if (!wrn(fd, a.data, a.datalen, a.datalen: i64)) { return -1; };
		};
		if (hasdatarelocs) {
			if (relad.n > 0u64) {
				if (!wrn(fd, relad.p, relad.n, relad.n: i64)) { return -1; };
			};
		};
	};
	if (sym.n > 0u64) {
		if (!wrn(fd, sym.p, sym.n, sym.n: i64)) { return -1; };
	};
	if (str_.n > 0u64) {
		if (!wrn(fd, str_.p, str_.n, str_.n: i64)) { return -1; };
	};
	if (shstr.n > 0u64) {
		if (!wrn(fd, shstr.p, shstr.n, shstr.n: i64)) { return -1; };
	};

	// Pad to 8 before shdrs.
	let written: u64 = EHDR_SZ + a.textlen + rela.n + sym.n + str_.n + shstr.n;
	if (hasdata) {
		written += a.datalen;
		if (hasdatarelocs) { written += relad.n; };
	};
	for ((written & 7u64) != 0u64) {
		wrdrop(fd, &zero, 1u64);
		written += 1u64;
	};

	// Section header table — 6 headers of 64 bytes each = 384 bytes.
	let shbuf: [64]u8;
	// SHT_NULL
	let sn: i32 = 0;
	for (sn < 64) { shbuf[sn] = 0u8; sn += 1; };
	wrdrop(fd, shbuf.ptr, 64u64);
	// .text
	sn = 0;
	for (sn < 64) { shbuf[sn] = 0u8; sn += 1; };
	wru32(shbuf.ptr,  0u64, shntext);
	wru32(shbuf.ptr,  4u64, SHT_PROGBITS_C);
	wru64(shbuf.ptr,  8u64, SHF_ALLOC | SHF_EXECINSTR);
	wru64(shbuf.ptr, 24u64, offtext);
	wru64(shbuf.ptr, 32u64, a.textlen);
	wru64(shbuf.ptr, 48u64, 1u64);	// sh_addralign
	wrdrop(fd, shbuf.ptr, 64u64);
	// .rela.text
	sn = 0;
	for (sn < 64) { shbuf[sn] = 0u8; sn += 1; };
	wru32(shbuf.ptr,  0u64, shnrela);
	wru32(shbuf.ptr,  4u64, SHT_RELA_C);
	wru64(shbuf.ptr,  8u64, SHF_INFO_LINK);
	wru64(shbuf.ptr, 24u64, offrela);
	wru64(shbuf.ptr, 32u64, rela.n);
	wru32(shbuf.ptr, 40u64, SH_SYMTAB: u32);	// sh_link
	wru32(shbuf.ptr, 44u64, 1u32);		// sh_info = .text idx
	wru64(shbuf.ptr, 48u64, 8u64);
	wru64(shbuf.ptr, 56u64, RELA_SZ);
	wrdrop(fd, shbuf.ptr, 64u64);
	if (hasdata) {
		// .data
		sn = 0;
		for (sn < 64) { shbuf[sn] = 0u8; sn += 1; };
		wru32(shbuf.ptr,  0u64, shndata);
		wru32(shbuf.ptr,  4u64, SHT_PROGBITS_C);
		wru64(shbuf.ptr,  8u64, SHF_ALLOC | SHF_WRITE);
		wru64(shbuf.ptr, 24u64, offdata);
		wru64(shbuf.ptr, 32u64, a.datalen);
		wru64(shbuf.ptr, 48u64, 8u64);	// sh_addralign
		wrdrop(fd, shbuf.ptr, 64u64);
		if (hasdatarelocs) {
			// .rela.data
			sn = 0;
			for (sn < 64) { shbuf[sn] = 0u8; sn += 1; };
			wru32(shbuf.ptr,  0u64, shnrelad);
			wru32(shbuf.ptr,  4u64, SHT_RELA_C);
			wru64(shbuf.ptr,  8u64, SHF_INFO_LINK);
			wru64(shbuf.ptr, 24u64, offrelad);
			wru64(shbuf.ptr, 32u64, relad.n);
			wru32(shbuf.ptr, 40u64, SH_SYMTAB: u32);
			wru32(shbuf.ptr, 44u64, SH_DATA: u32);	// applies to .data
			wru64(shbuf.ptr, 48u64, 8u64);
			wru64(shbuf.ptr, 56u64, RELA_SZ);
			wrdrop(fd, shbuf.ptr, 64u64);
		};
	};
	// .symtab
	sn = 0;
	for (sn < 64) { shbuf[sn] = 0u8; sn += 1; };
	wru32(shbuf.ptr,  0u64, shnsymtab);
	wru32(shbuf.ptr,  4u64, SHT_SYMTAB_C);
	wru64(shbuf.ptr, 24u64, offsym);
	wru64(shbuf.ptr, 32u64, sym.n);
	wru32(shbuf.ptr, 40u64, SH_STRTAB: u32);	// sh_link
	wru32(shbuf.ptr, 44u64, 1u32);	// sh_info = one local (STN_UNDEF)
	wru64(shbuf.ptr, 48u64, 8u64);
	wru64(shbuf.ptr, 56u64, SYM_SZ);
	wrdrop(fd, shbuf.ptr, 64u64);
	// .strtab
	sn = 0;
	for (sn < 64) { shbuf[sn] = 0u8; sn += 1; };
	wru32(shbuf.ptr,  0u64, shnstrtab);
	wru32(shbuf.ptr,  4u64, SHT_STRTAB_C);
	wru64(shbuf.ptr, 24u64, offstr);
	wru64(shbuf.ptr, 32u64, str_.n);
	wru64(shbuf.ptr, 48u64, 1u64);
	wrdrop(fd, shbuf.ptr, 64u64);
	// .shstrtab
	sn = 0;
	for (sn < 64) { shbuf[sn] = 0u8; sn += 1; };
	wru32(shbuf.ptr,  0u64, shnshstrtab);
	wru32(shbuf.ptr,  4u64, SHT_STRTAB_C);
	wru64(shbuf.ptr, 24u64, offshstr);
	wru64(shbuf.ptr, 32u64, shstr.n);
	wru64(shbuf.ptr, 48u64, 1u64);
	wrdrop(fd, shbuf.ptr, 64u64);

	return 0;
};

// selfhost/cmd/w6a/main.ww — port of cmd/w6a/main.c.
//
// w6a = amd64 assembler. Read .s, parse, encode, emit ELF .o.
//
//   w6a_ww -o file.o file.s

package main;

import os;
import rt;
import strings;
import opcodes;
import lex;
import parse;
import asm;
import obj;

fn cstreq(a: *u8, lit: str) bool = {
	let n: u64 = lit.len: u64;
	let i: u64 = 0u64;
	for (i < n) {
		let li: i32 = i: i32;
		if (a[i] != lit[li]) { return false; };
		i += 1u64;
	};
	if (a[i] != 0u8) { return false; };
	return true;
};

fn cstrlen(p: *u8) u64 = {
	let n: u64 = 0u64;
	for (p[n] != 0u8) { n += 1u64; };
	return n;
};

// pathstr — view a NUL-terminated *u8 as a str. Bridges argv-style
// callers to lib/os entrypoints (str post-task-#23).
fn pathstr(p: *u8) str = {
	let r: str;
	r.ptr = p;
	r.len = cstrlen(p): i32;
	return r;
};

// Slurp the whole file into a fresh buffer.
fn slurp(path: *u8) (*u8, u64) = {
	let fd: i32 = os.open(pathstr(path), os.flag.RDONLY, 0i32);
	if (fd < 0) { return nil, 0u64; };
	let szr: (i64 | os.oserror) = os.filesize(fd);
	let n: i64 = 0i64;
	match (szr) {
	case let v: i64 => n = v;
	case let e: os.oserror => { os.close(fd); return nil, 0u64; };
	};
	let nz: u64 = n: u64;
	let buf: []u8 = alloc([], nz + 1u64)!;
	buf.len = (nz + 1u64): i32;
	let rr: (i64 | os.oserror) = os.readall(fd, buf.ptr, nz);
	os.close(fd);
	let got: i64 = 0i64;
	match (rr) {
	case let v: i64 => got = v;
	case let e: os.oserror => return nil, 0u64;
	};
	if (got != n) { return nil, 0u64; };
	buf[nz] = 0u8;
	return buf.ptr, nz;
};

export fn main(argc: i32, argv: **u8) i32 = {
	let src: *u8 = nil;
	let out: *u8 = nil;

	let i: i32 = 1;
	for (i < argc) {
		let a: *u8 = argv[i];
		if (cstreq(a, "-o")) {
			i += 1;
			if (i >= argc) {
				os.write(2, "w6a: -o requires arg\n".ptr, 20u64);
				return 2;
			};
			out = argv[i];
		} else { if (a[0u64] == 45u8) {
			os.write(2, "w6a: unknown flag\n".ptr, 17u64);
			return 2;
		} else {
			if (src != nil) {
				os.write(2, "w6a: only one input\n".ptr, 19u64);
				return 2;
			};
			src = a;
		}; };
		i += 1;
	};

	if (src == nil) {
		os.write(2, "usage: w6a_ww -o file.o file.s\n".ptr, 30u64);
		return 2;
	};
	if (out == nil) {
		os.write(2, "w6a: missing -o\n".ptr, 15u64);
		return 2;
	};

	let buf: *u8;
	let blen: u64;
	buf, blen = slurp(src);
	if (buf == nil) {
		os.write(2, "w6a: cannot read input\n".ptr, 22u64);
		return 1;
	};

	let s: asm_;
	let nlen: u64 = cstrlen(src);
	let view: str;
	view.ptr = src;
	view.len = nlen: i32;
	let fname: str = strings.dup(view);
	init(&s, fname, buf, blen);

	if (parse(&s) != 0) { return 1; };
	if (encode(&s) != 0) { return 1; };

	// Open output for write.
	let fd: i32 = os.open(pathstr(out), os.flag.WRONLY | os.flag.CREATE | os.flag.TRUNC, 420i32);	// 0o644
	if (fd < 0) {
		os.write(2, "w6a: cannot open output\n".ptr, 23u64);
		return 1;
	};
	let rc: i32 = emitelf(&s, fd);
	os.close(fd);
	return rc;
};