github.com/primecitizens/pcz/std@v0.2.1/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  func Log10(x float64) float64 {
    10  	return log10(x)
    11  }
    12  
    13  func log10(x float64) float64 {
    14  	return Log(x) * (1 / Ln10)
    15  }
    16  
    17  // Log2 returns the binary logarithm of x.
    18  // The special cases are the same as for Log.
    19  func Log2(x float64) float64 {
    20  	return log2(x)
    21  }
    22  
    23  func log2(x float64) float64 {
    24  	frac, exp := Frexp(x)
    25  	// Make sure exact powers of two give an exact answer.
    26  	// Don't depend on Log(0.5)*(1/Ln2)+exp being exactly exp-1.
    27  	if frac == 0.5 {
    28  		return float64(exp - 1)
    29  	}
    30  	return Log(frac)*(1/Ln2) + float64(exp)
    31  }