ww/lib/math/checked/saturating.ww

// math/checked (saturating) — clamp-on-overflow arithmetic. Ported from
// Hare's math::checked saturating siblings
// (ref/hare/math/checked/saturating.ha). Part of the same `checked`
// module as checked.ww. Each sat_* clamps to the type's range on
// overflow instead of wrapping.
//
// Three ww adaptations vs Hare, all forced by language differences, none
// behavioral:
//   - no if-as-expression (N_IF is statement-only, see strings.ww), so
//     Hare's `return if (c) X else Y` becomes an if-statement.
//   - unsigned overflow tests rely on inline wraparound in Hare; ww
//     truncates sub-word arithmetic only on store to a typed lvalue, so
//     the wrap is forced through a typed `res`.
//   - the mul overflow compares need an explicit widening cast (no
//     implicit promotion in ww).
//
// Deferred (faithful subset, Hare splits per type): sat_subu8/16/32/64
// (reference types::U*_MIN, not yet exported by lib/types); sat_*z (no
// `size` type, #85); sat_muli64/sat_mulu64/sat_muli/sat_mulu (need
// math::mulu64); int/uint native-width sat_* (ww int is 64-bit — a width
// divergence in the overflow boundary).

package checked;

import types;

export fn sat_addi8(a: i8, b: i8) i8 = {
	let res: i8 = a + b;
	if (a < 0 == b < 0 && a < 0 != res < 0) {
		if (res < 0) { return types.I8_MAX; };
		return types.I8_MIN;
	};
	return res;
};

export fn sat_addi16(a: i16, b: i16) i16 = {
	let res: i16 = a + b;
	if (a < 0 == b < 0 && a < 0 != res < 0) {
		if (res < 0) { return types.I16_MAX; };
		return types.I16_MIN;
	};
	return res;
};

export fn sat_addi32(a: i32, b: i32) i32 = {
	let res: i32 = a + b;
	if (a < 0 == b < 0 && a < 0 != res < 0) {
		if (res < 0) { return types.I32_MAX; };
		return types.I32_MIN;
	};
	return res;
};

export fn sat_addi64(a: i64, b: i64) i64 = {
	let res: i64 = a + b;
	if (a < 0 == b < 0 && a < 0 != res < 0) {
		if (res < 0) { return types.I64_MAX; };
		return types.I64_MIN;
	};
	return res;
};

export fn sat_addu8(a: u8, b: u8) u8 = {
	let res: u8 = a + b;
	if (res < a) { return types.U8_MAX; };
	return res;
};

export fn sat_addu16(a: u16, b: u16) u16 = {
	let res: u16 = a + b;
	if (res < a) { return types.U16_MAX; };
	return res;
};

export fn sat_addu32(a: u32, b: u32) u32 = {
	let res: u32 = a + b;
	if (res < a) { return types.U32_MAX; };
	return res;
};

export fn sat_addu64(a: u64, b: u64) u64 = {
	let res: u64 = a + b;
	if (res < a) { return types.U64_MAX; };
	return res;
};

export fn sat_subi8(a: i8, b: i8) i8 = {
	let res: i8 = a - b;
	if (a < 0 != b < 0 && a < 0 != res < 0) {
		if (res < 0) { return types.I8_MAX; };
		return types.I8_MIN;
	};
	return res;
};

export fn sat_subi16(a: i16, b: i16) i16 = {
	let res: i16 = a - b;
	if (a < 0 != b < 0 && a < 0 != res < 0) {
		if (res < 0) { return types.I16_MAX; };
		return types.I16_MIN;
	};
	return res;
};

export fn sat_subi32(a: i32, b: i32) i32 = {
	let res: i32 = a - b;
	if (a < 0 != b < 0 && a < 0 != res < 0) {
		if (res < 0) { return types.I32_MAX; };
		return types.I32_MIN;
	};
	return res;
};

export fn sat_subi64(a: i64, b: i64) i64 = {
	let res: i64 = a - b;
	if (a < 0 != b < 0 && a < 0 != res < 0) {
		if (res < 0) { return types.I64_MAX; };
		return types.I64_MIN;
	};
	return res;
};

export fn sat_muli8(a: i8, b: i8) i8 = {
	let fullres: int = a: int * b: int;
	let res: i8 = fullres: i8;
	if (res: int != fullres) {
		if (res < 0) { return types.I8_MAX; };
		return types.I8_MIN;
	};
	return res;
};

export fn sat_muli16(a: i16, b: i16) i16 = {
	let fullres: int = a: int * b: int;
	let res: i16 = fullres: i16;
	if (res: int != fullres) {
		if (res < 0) { return types.I16_MAX; };
		return types.I16_MIN;
	};
	return res;
};

export fn sat_muli32(a: i32, b: i32) i32 = {
	let fullres: i64 = a: i64 * b: i64;
	let res: i32 = fullres: i32;
	if (res: i64 != fullres) {
		if (res < 0) { return types.I32_MAX; };
		return types.I32_MIN;
	};
	return res;
};

export fn sat_mulu8(a: u8, b: u8) u8 = {
	let res: uint = a: uint * b: uint;
	if (res > (types.U8_MAX): uint) { return types.U8_MAX; };
	return res: u8;
};

export fn sat_mulu16(a: u16, b: u16) u16 = {
	let res: uint = a: uint * b: uint;
	if (res > (types.U16_MAX): uint) { return types.U16_MAX; };
	return res: u16;
};

export fn sat_mulu32(a: u32, b: u32) u32 = {
	let res: u64 = a: u64 * b: u64;
	if (res > (types.U32_MAX): u64) { return types.U32_MAX; };
	return res: u32;
};