Source file src/math/logb.go

Documentation: math

		 1  // Copyright 2010 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  // Logb returns the binary exponent of x.
		 8  //
		 9  // Special cases are:
		10  //	Logb(±Inf) = +Inf
		11  //	Logb(0) = -Inf
		12  //	Logb(NaN) = NaN
		13  func Logb(x float64) float64 {
		14  	// special cases
		15  	switch {
		16  	case x == 0:
		17  		return Inf(-1)
		18  	case IsInf(x, 0):
		19  		return Inf(1)
		20  	case IsNaN(x):
		21  		return x
		22  	}
		23  	return float64(ilogb(x))
		24  }
		25  
		26  // Ilogb returns the binary exponent of x as an integer.
		27  //
		28  // Special cases are:
		29  //	Ilogb(±Inf) = MaxInt32
		30  //	Ilogb(0) = MinInt32
		31  //	Ilogb(NaN) = MaxInt32
		32  func Ilogb(x float64) int {
		33  	// special cases
		34  	switch {
		35  	case x == 0:
		36  		return MinInt32
		37  	case IsNaN(x):
		38  		return MaxInt32
		39  	case IsInf(x, 0):
		40  		return MaxInt32
		41  	}
		42  	return ilogb(x)
		43  }
		44  
		45  // logb returns the binary exponent of x. It assumes x is finite and
		46  // non-zero.
		47  func ilogb(x float64) int {
		48  	x, exp := normalize(x)
		49  	return int((Float64bits(x)>>shift)&mask) - bias + exp
		50  }
		51  

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