w6c+w6a+selfhost+lib: cgen+asm bugs surfaced by hash modules

Seven fixes across the toolchain, plus three new lib/hash modules
(adler32, crc16, crc32) that surfaced them.

  1. `~x` on u8/u16/u32 left the upper bits set: NOTQ inverts the
     whole 64-bit register and nothing trimmed it back to type
     width, so a returned `u16` would compare 64-bit against a
     typed literal and disagree. Both stages now mask after NOTQ
     for narrow unsigned: AND $0xFF/0xFFFF for u8/u16, MOVL r,r for
     u32 (ANDQ $0xFFFFFFFF sign-extends imm32 and is a no-op).
     Signed narrows stay sign-extended and need no fix-up. See
     cmd/w6c/cgen.c N_UN TK_TILDE and selfhost cgenexpr.ww cgun
     TK_TILDE with new nodeprimwidth helper.

  2. w6a had no D_CONST immediate path for ANDQ / ORQ. cgen would
     emit `ANDQ $65535, AX` and the rr encoder silently wrote
     `21 /r` with garbage reg fields — the mask never happened.
     Added `81 /4` (AND) and `81 /1` (OR) imm32 paths in both
     cstage and selfhost w6a. The ~width fix above depends on this.

  3. `s: []u8` cast as a direct fn argument produced a 0-length
     slice. cgexpr for N_CAST left (AX=ptr, BX=len) from the str
     source but never set CX (cap), and the arg-push fallback only
     pushed AX. cgcast now synthesises CX=BX when target is slice
     and source is str; node_isslice / arg-push recognise
     cast-to-slice and emit the full (cap, len, ptr) triple. Both
     stages.

  4. `*[N]T` element-store used 8-byte stride + MOVQ regardless of
     T's width. Indexing `buf: *[4]u16` would step 8 bytes and
     write 8 bytes per element. Added idx_eff (drills *[N]T → T)
     in cstage and the matching pointer-array drill in selfhost
     elemsizeof. Also added MOVW / MOVZWQ / MOVSWQ to w6c, w6a,
     and selfhost mirrors so 2-byte element stores/loads use the
     right opcode (was falling through to MOVQ and trailing 6 bytes
     into the next slot).

  5. Slicing a top-level fixed array (`g[0:n]` where `g: [N]T` is
     a global) computed the base from BP instead of the symbol —
     localfind returned 0 and the cgen treated it as a local at
     offset 0. Both N_SLICE-as-expression (cgslice) and N_SLICE-
     as-call-arg paths now check let_islet / letvartnode and emit
     LEAQ name(SB) when the base is a global array (or MOVQ
     name(SB) for a global slice/pointer base). Both stages.

  6. Top-level `let arr: [N]T = [v0, v1, ...]` link-failed on
     cstage — emit_lets bailed when it saw N_ARRLIT init on an
     array type, and the sz==8 scalar path then misemitted any
     8-byte-sized array (e.g. [4]u16, [8]u8) as a single quad.
     emit_lets now walks N_ARRLIT, evaluates each element as an
     int/rune/bool/nil literal, packs per-element bytes
     little-endian, and honours the trailing `...` repeat marker.
     Selfhost already handled the literal-init path; fixed the
     parallel sz==8 duplicate-DATAW emit on its side (the array
     and the scalar paths both fired, last write winning at link
     but the duplicate broke cross-stage byte-identicality on user
     code with this shape).

  7. w6a's per-line input buffer was a 1KB stack `char buf[1024]`.
     A `DATAW` for a [256]u16 emits ~2080 bytes on one line, which
     truncated mid-escape; the assembler then re-parsed the
     remaining tail as garbage opcodes ("unknown opcode"). Bumped
     cstage w6a to a 32K static buffer (selfhost w6a already
     allocated per-line via amalloc).

  lib: lib/hash/adler32, lib/hash/crc16, lib/hash/crc32 — pure
  buffer-subset shape (matching lib/hash/fnv), with per-module
  *_test.ww runnable via `ww test lib/hash/<name>`. Adler-32 plus
  CRC-16 (CCITT/CMDA2000/DECT/ANSI) and CRC-32 (IEEE/Castagnoli/
  Koopman) cover Hare's reference vectors bit-for-bit. Wired into
  test/wcc/900_stdlib.c. .gitignore: lib/**/*.s,*.o so `ww test`
  droppings stay untracked.

`make test` (26/26), `make bootstrap` (ww2≡ww3≡ww4), and per-module
`ww test` all pass. cgen output is byte-identical across cstage and
selfhost for every repro that previously diverged.

selfhost/cmd/wcc/cgenutil.ww

@@ -235,10 +235,20 @@ fn pushargsrev(c: *cgen, arg: *node, param: *node) i32 = {
 		let lo: *node = arg.rhs;
 		let hi: *node = arg.cond;
 		let baselocal: *local = nil;
+		let globaltn: *node = nil;
+		let globalname: str;
+		globalname.ptr = nil; globalname.len = 0;
 		if (base != nil) {
 			if (base.kind == nkind.N_IDENT) {
 				let bn: str = base.str;
 				baselocal = localfindnode(c, bn);
+				if (baselocal == nil) {
+					let gt: *node = letvartnode(c, bn);
+					if (gt != nil) {
+						globaltn = gt;
+						globalname = bn;
+					};
+				};
 			};
 		};
 		// base address → push
@@ -259,9 +269,19 @@ fn pushargsrev(c: *cgen, arg: *node, param: *node) i32 = {
 				emitoff(baselocal.off: i64);
 				emitline("(BP), AX\n");
 			};
+		} else { if (globaltn != nil) {
+			if (globaltn.kind == nkind.N_TARRAY) {
+				emitline("\tLEAQ\t");
+				emitsymname(c, globalname);
+				emitline("(SB), AX\n");
+			} else {
+				emitline("\tMOVQ\t");
+				emitsymname(c, globalname);
+				emitline("(SB), AX\n");
+			};
 		} else {
 			cgexpr(c, base);
-		};
+		};};
 		emitline("\tPUSHQ\tAX\n");
 		// hi (default base length) → push
 		if (hi != nil) {
@@ -290,9 +310,25 @@ fn pushargsrev(c: *cgen, arg: *node, param: *node) i32 = {
 					};
 				};};};
 			};
+		} else { if (globaltn != nil) {
+			if (globaltn.kind == nkind.N_TARRAY) {
+				let lenn: *node = globaltn.rhs;
+				if (lenn != nil) {
+					if (lenn.kind == nkind.N_INTLIT) {
+						emitline("\tMOVQ\t$");
+						emituint(lenn.uval);
+						emitline(", AX\n");
+					};
+				};
+			} else { if (globaltn.kind == nkind.N_TSLICE) {
+				emitline("\tLEAQ\t");
+				emitsymname(c, globalname);
+				emitline("(SB), CX\n");
+				emitline("\tMOVQ\t8(CX), AX\n");
+			};};
 		} else {
 			emitline("\tMOVQ\t$0, AX\n");
-		};};
+		};};};
 		emitline("\tPUSHQ\tAX\n");
 		// lo (default 0) → AX
 		if (lo != nil) { cgexpr(c, lo); }
@@ -376,6 +412,7 @@ fn nodeisslice(c: *cgen, n: *node) bool = {
 		return false;
 	};
 	if (k == nkind.N_SLICE) { return true; };
+	if (k == nkind.N_CAST) { return isslicetype(c, n.rhs); };
 	return false;
 };
 
@@ -733,6 +770,11 @@ fn elemsizeof(t: *node) i32 = {
 		return 1;
 	};
 	if (elem == nil) { return 1; };
+	// `*[N]T`: drill through the pointer into the array's element so
+	// indexing scales by T's width, not the whole-array byte size.
+	if (elem.kind == nkind.N_TARRAY) {
+		if (elem.lhs != nil) { elem = elem.lhs; };
+	};
 	if (elem.kind == nkind.N_TNAME) {
 		let nm: str = elem.str;
 		// str element is 16B (ptr+len). primsize returns 0 for it.
@@ -855,6 +897,35 @@ fn nodeisunsigned(c: *cgen, n: *node) bool = {
 	};
 	return false;
 };
+
+// nodeprimwidth — primitive byte width of an expression, or 0 if not
+// statically determinable. Mirrors nodeisunsigned's structural walk.
+// Used by cgun TK_TILDE to clamp narrow unsigned ~ results to type
+// width (NOTQ inverts the full 64-bit register).
+fn nodeprimwidth(c: *cgen, n: *node) i32 = {
+	if (n == nil) { return 0; };
+	let k: nkind = n.kind;
+	if (k == nkind.N_IDENT) {
+		let lc: *local = localfindnode(c, n.str);
+		if (lc != nil) {
+			let tn: *node = lc.tnode;
+			if (tn != nil) {
+				if (tn.kind == nkind.N_TNAME) { return primsize(tn.str); };
+			};
+		};
+		return 0;
+	};
+	if (k == nkind.N_CAST) {
+		let tn: *node = n.rhs;
+		if (tn != nil) {
+			if (tn.kind == nkind.N_TNAME) { return primsize(tn.str); };
+		};
+		return 0;
+	};
+	if (k == nkind.N_UN) { return nodeprimwidth(c, n.lhs); };
+	return 0;
+};
+
 // ---- type-driven slot sizing ----------------------------------------
 
 fn structlookup(c: *cgen, name: str) *structinfo = {