ldexp.go
1.06 KB
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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
// Ldexp is the inverse of Frexp.
// It returns frac × 2**exp.
//
// Special cases are:
// Ldexp(±0, exp) = ±0
// Ldexp(±Inf, exp) = ±Inf
// Ldexp(NaN, exp) = NaN
//extern ldexp
func libc_ldexp(float64, int) float64
func Ldexp(frac float64, exp int) float64 {
r := libc_ldexp(frac, exp)
return r
}
func ldexp(frac float64, exp int) float64 {
// special cases
switch {
case frac == 0:
return frac // correctly return -0
case IsInf(frac, 0) || IsNaN(frac):
return frac
}
frac, e := normalize(frac)
exp += e
x := Float64bits(frac)
exp += int(x>>shift)&mask - bias
if exp < -1074 {
return Copysign(0, frac) // underflow
}
if exp > 1023 { // overflow
if frac < 0 {
return Inf(-1)
}
return Inf(1)
}
var m float64 = 1
if exp < -1022 { // denormal
exp += 52
m = 1.0 / (1 << 52) // 2**-52
}
x &^= mask << shift
x |= uint64(exp+bias) << shift
return m * Float64frombits(x)
}