libgo/go/math/pow10.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 // This table might overflow 127-bit exponent representations.
   8 // In that case, truncate it after 1.0e38.
   9 var pow10tab [70]float64
  10
  11 // Pow10 returns 10**e, the base-10 exponential of e.
  12 //
  13 // Special cases are:
  14 //      Pow10(e) = +Inf for e > 309
  15 //      Pow10(e) = 0 for e < -324
  16 func Pow10(e int) float64 {
  17         if e <= -325 {
  18                 return 0
  19         } else if e > 309 {
  20                 return Inf(1)
  21         }
  22
  23         if e < 0 {
  24                 return 1 / Pow10(-e)
  25         }
  26         if e < len(pow10tab) {
  27                 return pow10tab[e]
  28         }
  29         m := e / 2
  30         return Pow10(m) * Pow10(e-m)
  31 }
  32
  33 func init() {
  34         pow10tab[0] = 1.0e0
  35         pow10tab[1] = 1.0e1
  36         for i := 2; i < len(pow10tab); i++ {
  37                 m := i / 2
  38                 pow10tab[i] = pow10tab[m] * pow10tab[i-m]
  39         }
  40 }