diff --git a/lib/math/floats.ww b/lib/math/floats.ww
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+// floats — f64 classification, sign, and bit-reinterpret core. Ported
+// from ref/hare/math/floats.ha (fold-1: the minimal classify/sign/bits
+// surface). f32 variants, NAN/INF + magnitude consts, and
+// frexp/ldexp/normalize/modfrac/nextafter are deferred to a later fold.
+
+package math;
+
+// Returns the binary representation of the given f64.
+// ref/hare/math/floats.ha:5
+export fn f64bits(n: f64) u64 = {
+	let p: *u64 = (&n): *u64;
+	return *p;
+};
+
+// Returns f64 with the given binary representation.
+// ref/hare/math/floats.ha:11
+export fn f64frombits(n: u64) f64 = {
+	let p: *f64 = (&n): *f64;
+	return *p;
+};
+
+// 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 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));
+};