Source file src/math/log10.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  // Log10 returns the decimal logarithm of x.
		 8  // The special cases are the same as for Log.
		 9  func Log10(x float64) float64 {
		10  	if haveArchLog10 {
		11  		return archLog10(x)
		12  	}
		13  	return log10(x)
		14  }
		15  
		16  func log10(x float64) float64 {
		17  	return Log(x) * (1 / Ln10)
		18  }
		19  
		20  // Log2 returns the binary logarithm of x.
		21  // The special cases are the same as for Log.
		22  func Log2(x float64) float64 {
		23  	if haveArchLog2 {
		24  		return archLog2(x)
		25  	}
		26  	return log2(x)
		27  }
		28  
		29  func log2(x float64) float64 {
		30  	frac, exp := Frexp(x)
		31  	// Make sure exact powers of two give an exact answer.
		32  	// Don't depend on Log(0.5)*(1/Ln2)+exp being exactly exp-1.
		33  	if frac == 0.5 {
		34  		return float64(exp - 1)
		35  	}
		36  	return Log(frac)*(1/Ln2) + float64(exp)
		37  }
		38  

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