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
5package math
6
7// Log10 returns the decimal logarithm of x.
8// The special cases are the same as for Log.
9
10//extern log10
11func libc_log10(float64) float64
12
13func Log10(x float64) float64 {
14	return libc_log10(x)
15}
16
17func log10(x float64) float64 {
18	return Log(x) * (1 / Ln10)
19}
20
21// Log2 returns the binary logarithm of x.
22// The special cases are the same as for Log.
23
24func Log2(x float64) float64 {
25	return log2(x)
26}
27
28func log2(x float64) float64 {
29	frac, exp := Frexp(x)
30	// Make sure exact powers of two give an exact answer.
31	// Don't depend on Log(0.5)*(1/Ln2)+exp being exactly exp-1.
32	if frac == 0.5 {
33		return float64(exp - 1)
34	}
35	return Log(frac)*(1/Ln2) + float64(exp)
36}
37