libgo/go/math/logb.go

   1 // Copyright 2010 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 // Logb(x) returns the binary exponent of x.
   8 //
   9 // Special cases are:
  10 //      Logb(±Inf) = +Inf
  11 //      Logb(0) = -Inf
  12 //      Logb(NaN) = NaN
  13 func Logb(x float64) float64 {
  14         // special cases
  15         switch {
  16         case x == 0:
  17                 return Inf(-1)
  18         case IsInf(x, 0):
  19                 return Inf(1)
  20         case IsNaN(x):
  21                 return x
  22         }
  23         return float64(ilogb(x))
  24 }
  25
  26 // Ilogb(x) returns the binary exponent of x as an integer.
  27 //
  28 // Special cases are:
  29 //      Ilogb(±Inf) = MaxInt32
  30 //      Ilogb(0) = MinInt32
  31 //      Ilogb(NaN) = MaxInt32
  32 func Ilogb(x float64) int {
  33         // special cases
  34         switch {
  35         case x == 0:
  36                 return MinInt32
  37         case IsNaN(x):
  38                 return MaxInt32
  39         case IsInf(x, 0):
  40                 return MaxInt32
  41         }
  42         return ilogb(x)
  43 }
  44
  45 // logb returns the binary exponent of x. It assumes x is finite and
  46 // non-zero.
  47 func ilogb(x float64) int {
  48         x, exp := normalize(x)
  49         return int((Float64bits(x)>>shift)&mask) - bias + exp
  50 }