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

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