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1 // Copyright 2009 The Go Authors. All rights reserved.
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2 // Use of this source code is governed by a BSD-style
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3 // license that can be found in the LICENSE file.
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4
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5 package math
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6
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7 // pow10tab stores the pre-computed values 10**i for i < 32.
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8 var pow10tab = [...]float64{
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9 1e00, 1e01, 1e02, 1e03, 1e04, 1e05, 1e06, 1e07, 1e08, 1e09,
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10 1e10, 1e11, 1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18, 1e19,
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11 1e20, 1e21, 1e22, 1e23, 1e24, 1e25, 1e26, 1e27, 1e28, 1e29,
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12 1e30, 1e31,
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13 }
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14
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15 // pow10postab32 stores the pre-computed value for 10**(i*32) at index i.
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16 var pow10postab32 = [...]float64{
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17 1e00, 1e32, 1e64, 1e96, 1e128, 1e160, 1e192, 1e224, 1e256, 1e288,
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18 }
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19
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20 // pow10negtab32 stores the pre-computed value for 10**(-i*32) at index i.
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21 var pow10negtab32 = [...]float64{
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22 1e-00, 1e-32, 1e-64, 1e-96, 1e-128, 1e-160, 1e-192, 1e-224, 1e-256, 1e-288, 1e-320,
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23 }
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24
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25 // Pow10 returns 10**n, the base-10 exponential of n.
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26 //
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27 // Special cases are:
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28 // Pow10(n) = 0 for n < -323
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29 // Pow10(n) = +Inf for n > 308
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30 func Pow10(n int) float64 {
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31 if 0 <= n && n <= 308 {
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32 return pow10postab32[uint(n)/32] * pow10tab[uint(n)%32]
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33 }
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34
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35 if -323 <= n && n <= 0 {
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36 return pow10negtab32[uint(-n)/32] / pow10tab[uint(-n)%32]
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37 }
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38
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39 // n < -323 || 308 < n
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40 if n > 0 {
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41 return Inf(1)
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42 }
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43
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44 // n < -323
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45 return 0
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46 }
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