libgo/go/math/frexp.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 // Frexp breaks f into a normalized fraction
   8 // and an integral power of two.
   9 // It returns frac and exp satisfying f == frac × 2**exp,
  10 // with the absolute value of frac in the interval [½, 1).
  11 //
  12 // Special cases are:
  13 //      Frexp(±0) = ±0, 0
  14 //      Frexp(±Inf) = ±Inf, 0
  15 //      Frexp(NaN) = NaN, 0
  16 func Frexp(f float64) (frac float64, exp int) {
  17         return frexp(f)
  18 }
  19
  20 func frexp(f float64) (frac float64, exp int) {
  21         // special cases
  22         switch {
  23         case f == 0:
  24                 return f, 0 // correctly return -0
  25         case IsInf(f, 0) || IsNaN(f):
  26                 return f, 0
  27         }
  28         f, exp = normalize(f)
  29         x := Float64bits(f)
  30         exp += int((x>>shift)&mask) - bias + 1
  31         x &^= mask << shift
  32         x |= (-1 + bias) << shift
  33         frac = Float64frombits(x)
  34         return
  35 }