move math out of runtime.

a step toward enforcing package boundaries,
necessary to eliminate global package name space.

R=r
DELTA=581  (310 added, 271 deleted, 0 changed)
OCL=35805
CL=35823

src/pkg/math/bits.go

@@ -0,0 +1,105 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package math
+
+const (
+	uvnan = 0x7FF0000000000001;
+	uvinf = 0x7FF0000000000000;
+	uvneginf = 0xFFF0000000000000;
+	mask = 0x7FF;
+	shift = 64 - 11 - 1;
+	bias = 1022;
+)
+
+// Inf returns positive infinity if sign >= 0, negative infinity if sign < 0.
+func Inf(sign int) float64 {
+	var v uint64;
+	if sign >= 0 {
+		v = uvinf;
+	} else {
+		v = uvneginf;
+	}
+	return Float64frombits(v);
+}
+
+// NaN returns an IEEE 754 ``not-a-number'' value.
+func NaN() float64 {
+	return Float64frombits(uvnan);
+}
+
+// IsNaN returns whether f is an IEEE 754 ``not-a-number'' value.
+func IsNaN(f float64) (is bool) {
+	x := Float64bits(f);
+	return uint32(x>>shift) & mask == mask && x != uvinf && x != uvneginf;
+}
+
+// IsInf returns whether f is an infinity, according to sign.
+// If sign > 0, IsInf returns whether f is positive infinity.
+// If sign < 0, IsInf returns whether f is negative infinity.
+// If sign == 0, IsInf returns whether f is either infinity.
+func IsInf(f float64, sign int) bool {
+	x := Float64bits(f);
+	return sign >= 0 && x == uvinf || sign <= 0 && x == uvneginf;
+}
+
+// Frexp breaks f into a normalized fraction
+// and an integral power of two.
+// It returns frac and exp satisfying f == frac × 2<sup>exp</sup>,
+// with the absolute value of frac in the interval [½, 1).
+func Frexp(f float64) (frac float64, exp int) {
+	if f == 0 {
+		return;
+	}
+	x := Float64bits(f);
+	exp = int((x>>shift)&mask) - bias;
+	x &^= mask<<shift;
+	x |= bias<<shift;
+	frac = Float64frombits(x);
+	return;
+}
+
+// Ldexp is the inverse of Frexp.
+// It returns frac × 2<sup>exp</sup>.
+func Ldexp(frac float64, exp int) float64 {
+	x := Float64bits(frac);
+	exp += int(x>>shift) & mask;
+	if exp <= 0 {
+		return 0;	// underflow
+	}
+	if exp >= mask {	// overflow
+		if frac < 0 {
+			return Inf(-1);
+		}
+		return Inf(1);
+	}
+	x &^= mask<<shift;
+	x |= uint64(exp)<<shift;
+	return Float64frombits(x);
+}
+
+// Modf returns integer and fractional floating-point numbers
+// that sum to f.
+// Integer and frac have the same sign as f.
+func Modf(f float64) (int float64, frac float64) {
+	if f < 1 {
+		if f < 0 {
+			int, frac = Modf(-f);
+			return -int, -frac;
+		}
+		return 0, f;
+	}
+
+	x := Float64bits(f);
+	e := uint(x>>shift)&mask - bias;
+
+	// Keep the top 11+e bits, the integer part; clear the rest.
+	if e < 64-11 {
+		x &^= 1<<(64-11-e) - 1;
+	}
+	int = Float64frombits(x);
+	frac = f - int;
+	return;
+}
+