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 } 41
