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].
9func Log10(x float64) float64 {
10	if haveArchLog10 {
11		return archLog10(x)
12	}
13	return log10(x)
14}
15
16func 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].
22func Log2(x float64) float64 {
23	if haveArchLog2 {
24		return archLog2(x)
25	}
26	return log2(x)
27}
28
29func 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