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bed6326a3c
- Make Log2 exact for powers of two. - Fix error tolerance function to make tolerance a function of the correct (expected) value. Fixes #9066. Change-Id: I0320a93ce4130deed1c7b7685627d51acb7bc56d Reviewed-on: https://go-review.googlesource.com/12230 Reviewed-by: Ian Lance Taylor <iant@golang.org>
28 lines
740 B
Go
28 lines
740 B
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package math
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// Log10 returns the decimal logarithm of x.
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// The special cases are the same as for Log.
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func Log10(x float64) float64
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func log10(x float64) float64 {
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return Log(x) * (1 / Ln10)
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}
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// Log2 returns the binary logarithm of x.
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// The special cases are the same as for Log.
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func Log2(x float64) float64
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func log2(x float64) float64 {
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frac, exp := Frexp(x)
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// Make sure exact powers of two give an exact answer.
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// Don't depend on Log(0.5)*(1/Ln2)+exp being exactly exp-1.
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if frac == 0.5 {
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return float64(exp - 1)
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}
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return Log(frac)*(1/Ln2) + float64(exp)
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}
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