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Source file src/math/pow10.go

Documentation: math

  // Copyright 2009 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  package math
  
  // pow10tab stores the pre-computed values 10**i for i < 32.
  var pow10tab = [...]float64{
  	1e00, 1e01, 1e02, 1e03, 1e04, 1e05, 1e06, 1e07, 1e08, 1e09,
  	1e10, 1e11, 1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18, 1e19,
  	1e20, 1e21, 1e22, 1e23, 1e24, 1e25, 1e26, 1e27, 1e28, 1e29,
  	1e30, 1e31,
  }
  
  // pow10postab32 stores the pre-computed value for 10**(i*32) at index i.
  var pow10postab32 = [...]float64{
  	1e00, 1e32, 1e64, 1e96, 1e128, 1e160, 1e192, 1e224, 1e256, 1e288,
  }
  
  // pow10negtab32 stores the pre-computed value for 10**(-i*32) at index i.
  var pow10negtab32 = [...]float64{
  	1e-00, 1e-32, 1e-64, 1e-96, 1e-128, 1e-160, 1e-192, 1e-224, 1e-256, 1e-288, 1e-320,
  }
  
  // Pow10 returns 10**n, the base-10 exponential of n.
  //
  // Special cases are:
  //	Pow10(n) =    0 for n < -323
  //	Pow10(n) = +Inf for n > 308
  func Pow10(n int) float64 {
  	if 0 <= n && n <= 308 {
  		return pow10postab32[uint(n)/32] * pow10tab[uint(n)%32]
  	}
  
  	if -323 <= n && n <= 0 {
  		return pow10negtab32[uint(-n)/32] / pow10tab[uint(-n)%32]
  	}
  
  	// n < -323 || 308 < n
  	if n > 0 {
  		return Inf(1)
  	}
  
  	// n < -323
  	return 0
  }
  

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