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// 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) {
// IEEE 754 says that only NaNs satisfy f != f.
// To avoid the floating-point hardware, could use:
// x := Float64bits(f);
// return uint32(x>>shift)&mask == mask && x != uvinf && x != uvneginf
return f != f
}
// 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 {
// Test for infinity by comparing against maximum float.
// To avoid the floating-point hardware, could use:
// x := Float64bits(f);
// return sign >= 0 && x == uvinf || sign <= 0 && x == uvneginf;
return sign >= 0 && f > MaxFloat64 || sign <= 0 && f < -MaxFloat64
}
// 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) {
// TODO(rsc): Remove manual inlining of IsNaN, IsInf
// when compiler does it for us
// special cases
switch {
case f == 0:
return
case f < -MaxFloat64 || f > MaxFloat64 || f != f: // IsInf(f, 0) || IsNaN(f):
frac = f
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 {
// TODO(rsc): Remove manual inlining of IsNaN, IsInf
// when compiler does it for us
// special cases
if frac != frac { // IsNaN(frac)
return NaN()
}
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)
}
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