34 lines
764 B
Go
34 lines
764 B
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.
|
||
func Ldexp(frac float64, exp int) float64 {
|
||
// TODO(rsc): Remove manual inlining of IsNaN, IsInf
|
||
// when compiler does it for us
|
||
// special cases
|
||
switch {
|
||
case frac == 0:
|
||
return frac // correctly return -0
|
||
case 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)
|
||
}
|