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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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