github.com/axw/llgo@v0.0.0-20160805011314-95b5fe4dca20/third_party/gofrontend/libgo/go/math/log10.go (about)

     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  
     5  package math
     6  
     7  // Log10 returns the decimal logarithm of x.
     8  // The special cases are the same as for Log.
     9  
    10  //extern log10
    11  func libc_log10(float64) float64
    12  
    13  func Log10(x float64) float64 {
    14  	return libc_log10(x)
    15  }
    16  
    17  func 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  
    24  func Log2(x float64) float64 {
    25  	return log2(x)
    26  }
    27  
    28  func 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  }