pow10.go

Documentation: math

		 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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