// Ported from Hare's math::checked (ref/hare/math/checked/checked.ha).
// add*/sub*/mul* return (result, overflow) with wrapping semantics. The
// saturating (clamp-on-overflow) siblings live in saturating.ww — same
// `checked` module.
//
// Subset of Hare's surface (Hare splits per type, so these are clean
// omissions, not divergences):
//   - size-typed *z variants (addz/subz/mulz): no `size` type yet (#85).
//   - int/uint native-width variants: ww int/uint are 64-bit (type.c),
//     so they'd silently behave like the i64/u64 forms — a width
//     divergence in the overflow boundary.
//   - 64-bit muls (muli64/mulu64/powi64) and the muli/mulu dispatchers:
//     need math::mulu64 (128-bit product), not yet exposed by lib/math.

package checked;

export fn addi8(a: i8, b: i8) (i8, bool) = {
	let res: i8 = a + b;
	let overflow = a < 0 == b < 0 && a < 0 != res < 0;
	return (res, overflow);
};

export fn addi16(a: i16, b: i16) (i16, bool) = {
	let res: i16 = a + b;
	let overflow = a < 0 == b < 0 && a < 0 != res < 0;
	return (res, overflow);
};

export fn addi32(a: i32, b: i32) (i32, bool) = {
	let res: i32 = a + b;
	let overflow = a < 0 == b < 0 && a < 0 != res < 0;
	return (res, overflow);
};

export fn addi64(a: i64, b: i64) (i64, bool) = {
	let res: i64 = a + b;
	let overflow = a < 0 == b < 0 && a < 0 != res < 0;
	return (res, overflow);
};

export fn addu8(a: u8, b: u8) (u8, bool) = {
	let res: u8 = a + b;
	let overflow = res < a;
	return (res, overflow);
};

export fn addu16(a: u16, b: u16) (u16, bool) = {
	let res: u16 = a + b;
	let overflow = res < a;
	return (res, overflow);
};

export fn addu32(a: u32, b: u32) (u32, bool) = {
	let res: u32 = a + b;
	let overflow = res < a;
	return (res, overflow);
};

export fn addu64(a: u64, b: u64) (u64, bool) = {
	let res: u64 = a + b;
	let overflow = res < a;
	return (res, overflow);
};

export fn subi8(a: i8, b: i8) (i8, bool) = {
	let res: i8 = a - b;
	let overflow = a < 0 != b < 0 && a < 0 != res < 0;
	return (res, overflow);
};

export fn subi16(a: i16, b: i16) (i16, bool) = {
	let res: i16 = a - b;
	let overflow = a < 0 != b < 0 && a < 0 != res < 0;
	return (res, overflow);
};

export fn subi32(a: i32, b: i32) (i32, bool) = {
	let res: i32 = a - b;
	let overflow = a < 0 != b < 0 && a < 0 != res < 0;
	return (res, overflow);
};

export fn subi64(a: i64, b: i64) (i64, bool) = {
	let res: i64 = a - b;
	let overflow = a < 0 != b < 0 && a < 0 != res < 0;
	return (res, overflow);
};

export fn subu8(a: u8, b: u8) (u8, bool) = {
	let res: u8 = a - b;
	let overflow = res > a;
	return (res, overflow);
};

export fn subu16(a: u16, b: u16) (u16, bool) = {
	let res: u16 = a - b;
	let overflow = res > a;
	return (res, overflow);
};

export fn subu32(a: u32, b: u32) (u32, bool) = {
	let res: u32 = a - b;
	let overflow = res > a;
	return (res, overflow);
};

export fn subu64(a: u64, b: u64) (u64, bool) = {
	let res: u64 = a - b;
	let overflow = res > a;
	return (res, overflow);
};

// muli8: Hare compares the truncated `res` against the full-width
// product directly (checked.ha:321 `res != fullres`), relying on its
// implicit i8->int promotion. ww has no implicit integer promotion
// (cmd/wcc/check.c unify_arith errors on differing concrete types), so
// the widening cast is written explicitly. Same shape in the muls below.
export fn muli8(a: i8, b: i8) (i8, bool) = {
	let fullres: int = a: int * b: int;
	let res: i8 = fullres: i8;
	let overflow = res: int != fullres;
	return (res, overflow);
};

export fn muli16(a: i16, b: i16) (i16, bool) = {
	let fullres: int = a: int * b: int;
	let res: i16 = fullres: i16;
	let overflow = res: int != fullres;
	return (res, overflow);
};

export fn muli32(a: i32, b: i32) (i32, bool) = {
	let fullres: i64 = a: i64 * b: i64;
	let res: i32 = fullres: i32;
	let overflow = res: i64 != fullres;
	return (res, overflow);
};

export fn mulu8(a: u8, b: u8) (u8, bool) = {
	let fullres: uint = a: uint * b: uint;
	let res: u8 = fullres: u8;
	let overflow = res: uint != fullres;
	return (res, overflow);
};

export fn mulu16(a: u16, b: u16) (u16, bool) = {
	let fullres: uint = a: uint * b: uint;
	let res: u16 = fullres: u16;
	let overflow = res: uint != fullres;
	return (res, overflow);
};

export fn mulu32(a: u32, b: u32) (u32, bool) = {
	let fullres: u64 = a: u64 * b: u64;
	let res: u32 = fullres: u32;
	let overflow = res: u64 != fullres;
	return (res, overflow);
};