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 // pow10tab stores the pre-computed values 10**i for i < 32. 8 var pow10tab = [...]float64{ 9 1e00, 1e01, 1e02, 1e03, 1e04, 1e05, 1e06, 1e07, 1e08, 1e09, 10 1e10, 1e11, 1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18, 1e19, 11 1e20, 1e21, 1e22, 1e23, 1e24, 1e25, 1e26, 1e27, 1e28, 1e29, 12 1e30, 1e31, 13 } 14 15 // pow10postab32 stores the pre-computed value for 10**(i*32) at index i. 16 var pow10postab32 = [...]float64{ 17 1e00, 1e32, 1e64, 1e96, 1e128, 1e160, 1e192, 1e224, 1e256, 1e288, 18 } 19 20 // pow10negtab32 stores the pre-computed value for 10**(-i*32) at index i. 21 var pow10negtab32 = [...]float64{ 22 1e-00, 1e-32, 1e-64, 1e-96, 1e-128, 1e-160, 1e-192, 1e-224, 1e-256, 1e-288, 1e-320, 23 } 24 25 // Pow10 returns 10**n, the base-10 exponential of n. 26 // 27 // Special cases are: 28 // Pow10(n) = 0 for n < -323 29 // Pow10(n) = +Inf for n > 308 30 func Pow10(n int) float64 { 31 if 0 <= n && n <= 308 { 32 return pow10postab32[uint(n)/32] * pow10tab[uint(n)%32] 33 } 34 35 if -323 <= n && n <= 0 { 36 return pow10negtab32[uint(-n)/32] / pow10tab[uint(-n)%32] 37 } 38 39 // n < -323 || 308 < n 40 if n > 0 { 41 return Inf(1) 42 } 43 44 // n < -323 45 return 0 46 } 47
