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