63 lines
1.5 KiB
Go
63 lines
1.5 KiB
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
|
||
|
||
// 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)
|
||
|
||
// Work around a bug in the implementation of ldexp on Solaris
|
||
// 9. If multiplying a negative number by 2 raised to a
|
||
// negative exponent underflows, we want to return negative
|
||
// zero, but the Solaris 9 implementation returns positive
|
||
// zero. This workaround can be removed when and if we no
|
||
// longer care about Solaris 9.
|
||
if r == 0 && frac < 0 && exp < 0 {
|
||
r = Copysign(0, frac)
|
||
}
|
||
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)
|
||
}
|