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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package math
// Log10 returns the decimal logarithm of x.
// The special cases are the same as for Log.
func Log10(x float64) float64 {
if haveArchLog10 {
return archLog10(x)
}
return log10(x)
}
func log10(x float64) float64 {
return Log(x) * (1 / Ln10)
}
// Log2 returns the binary logarithm of x.
// The special cases are the same as for Log.
func Log2(x float64) float64 {
if haveArchLog2 {
return archLog2(x)
}
return log2(x)
}
func log2(x float64) float64 {
frac, exp := Frexp(x)
// Make sure exact powers of two give an exact answer.
// Don't depend on Log(0.5)*(1/Ln2)+exp being exactly exp-1.
if frac == 0.5 {
return float64(exp - 1)
}
return Log(frac)*(1/Ln2) + float64(exp)
}
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