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 //
29 // Pow10(n) = 0 for n < -323
30 // Pow10(n) = +Inf for n > 308
31 func Pow10(n int) float64 {
32 if 0 <= n && n <= 308 {
33 return pow10postab32[uint(n)/32] * pow10tab[uint(n)%32]
34 }
35 36 if -323 <= n && n <= 0 {
37 return pow10negtab32[uint(-n)/32] / pow10tab[uint(-n)%32]
38 }
39 40 // n < -323 || 308 < n
41 if n > 0 {
42 return Inf(1)
43 }
44 45 // n < -323
46 return 0
47 }
48