libgo/go/math/ldexp.go

   1 // Copyright 2009 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 package math
   6
   7 // Ldexp is the inverse of Frexp.
   8 // It returns frac × 2**exp.
   9 func Ldexp(frac float64, exp int) float64 {
  10         // TODO(rsc): Remove manual inlining of IsNaN, IsInf
  11         // when compiler does it for us
  12         // special cases
  13         switch {
  14         case frac == 0:
  15                 return frac // correctly return -0
  16         case frac != frac: // IsNaN(frac):
  17                 return NaN()
  18         }
  19         x := Float64bits(frac)
  20         exp += int(x>>shift) & mask
  21         if exp <= 0 {
  22                 return 0 // underflow
  23         }
  24         if exp >= mask { // overflow
  25                 if frac < 0 {
  26                         return Inf(-1)
  27                 }
  28                 return Inf(1)
  29         }
  30         x &^= mask << shift
  31         x |= uint64(exp) << shift
  32         return Float64frombits(x)
  33 }