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-rw-r--r--src/math/log10.go27
1 files changed, 27 insertions, 0 deletions
diff --git a/src/math/log10.go b/src/math/log10.go
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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
+
+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
+
+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)
+}