src/pkg/math/bits.go

// 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;
}