ww/lib/math/floats.ww

// floats — f64 classification, sign, bit-reinterpret core, and the
// subnormal-normalize step of the f64 decompose half. Ported from
// ref/hare/math/floats.ha (fold-1: classify/sign/bits; fold-2a:
// issubnormalf64/normalizef64). frexpf64 (floats.ha:278) is held back: its
// Hare-exact zero guard `n == 0f64` miscompiles — a no-decimal `0f64`
// literal in an f64 comparison is materialized into a GPR and never moved
// to XMM, so the compare reads a stale operand (both stages identically,
// so the byte-id gates are blind to it). `0.0` would dodge it, but that is
// a workaround (CLAUDE.md rule 7); frexpf64 lands once the cgen bug is
// fixed. f32 variants, NAN/INF + magnitude consts, and the
// ldexp/modfrac/nextafter family (need f64 DIVIDE + the INF const) are
// deferred to a later fold.

package math;

// Returns the binary representation of the given f64.
// ref/hare/math/floats.ha:5. Parens around &n are load-bearing: ww's `:`
// cast binds tighter than unary `&`, so Hare's `*(&n: *u64)` would parse
// as `*(&(n: *u64))`; `(&n): *u64` reinterprets the address as intended.
export fn f64bits(n: f64) u64 = {
	return *((&n): *u64);
};

// Returns f64 with the given binary representation.
// ref/hare/math/floats.ha:11
export fn f64frombits(n: u64) f64 = {
	return *((&n): *f64);
};

// ref/hare/math/floats.ha:17,20,23 declare these as untyped int. ww has
// no untyped def (every def carries a type) and routes shift/bitwise
// through unify_arith, which rejects mixed operand types (cmd/wcc/
// check.c:769). The bit-structure consts are used only as u64 shift
// amounts and mask widths, so they are typed u64 here — the closest
// stand-in for Hare's untyped-int adapt at those use sites.

// The number of bits in the significand of the binary representation of f64.
export def F64_MANTISSA_BITS: u64 = 52;

// The number of bits in the exponent of the binary representation of f64.
export def F64_EXPONENT_BITS: u64 = 11;

// The bias of the exponent of the binary representation of f64. Subtract this
// from the exponent in the binary representation to get the actual exponent.
export def F64_EXPONENT_BIAS: u64 = 1023;

// Mask with each bit of an f64's mantissa set.
// ref/hare/math/floats.ha:37
export def F64_MANTISSA_MASK: u64 = (1 << F64_MANTISSA_BITS) - 1;

// Mask with each bit of an f64's exponent set.
// ref/hare/math/floats.ha:40
export def F64_EXPONENT_MASK: u64 = (1 << F64_EXPONENT_BITS) - 1;

// The mask that gets an f64's sign.
// ref/hare/math/floats.ha:75
def F64_SIGN_MASK: u64 = 1u64 << 63;

// Returns true if the given floating-point number is NaN.
// ref/hare/math/floats.ha:144 (Hare's expression body inlined into a
// block: ww has no expression-bodied fn form, only brace blocks).
export fn isnan(n: f64) bool = {
	return n != n;
};

// Returns true if the given floating-point number is infinite.
// ref/hare/math/floats.ha:147
export fn isinf(n: f64) bool = {
	const bits = f64bits(n);
	const mant = bits & F64_MANTISSA_MASK;
	const exp = bits >> F64_MANTISSA_BITS & F64_EXPONENT_MASK;
	return exp == F64_EXPONENT_MASK && mant == 0;
};

// Returns true if the given f64 is subnormal.
// ref/hare/math/floats.ha:179
export fn issubnormalf64(n: f64) bool = {
	const bits = f64bits(n);
	const mant = bits & F64_MANTISSA_MASK;
	const exp = bits >> F64_MANTISSA_BITS & F64_EXPONENT_MASK;
	return exp == 0 && mant != 0;
};

// Returns the absolute value of f64 n.
// ref/hare/math/floats.ha:195
export fn absf64(n: f64) f64 = {
	if (isnan(n)) {
		return n;
	};
	return f64frombits(f64bits(n) & ~F64_SIGN_MASK);
};

// Returns 1 if x is positive and -1 if x is negative. Note that zero is also
// signed.
// ref/hare/math/floats.ha:212
export fn signf64(x: f64) i64 = {
	if (f64bits(x) & F64_SIGN_MASK == 0) {
		return 1i64;
	} else {
		return -1i64;
	};
};

// Returns whether or not x is positive.
// ref/hare/math/floats.ha:231
export fn ispositivef64(x: f64) bool = {
	return signf64(x) == 1i64;
};

// Returns whether or not x is negative.
// ref/hare/math/floats.ha:237
export fn isnegativef64(x: f64) bool = {
	return signf64(x) == -1i64;
};

// Returns x, but with the sign of y.
// ref/hare/math/floats.ha:243
export fn copysignf64(x: f64, y: f64) f64 = {
	return f64frombits((f64bits(x) & ~F64_SIGN_MASK) |
		(f64bits(y) & F64_SIGN_MASK));
};

// Takes a potentially subnormal f64 n and returns a normal f64 normal_float
// and an exponent exp such that n == normal_float * 2^{exp}.
// ref/hare/math/floats.ha:256
export fn normalizef64(n: f64) (f64, i64) = {
	if (issubnormalf64(n)) {
		const factor = 1i64 << (F64_MANTISSA_BITS: i64);
		const normal_float = (n * (factor: f64));
		return (normal_float, -(F64_MANTISSA_BITS: i64));
	};
	return (n, 0);
};