Source file src/pkg/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	// 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	

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