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Source file src/math/logb.go

Documentation: math

  // Copyright 2010 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  package math
  
  // Logb returns the binary exponent of x.
  //
  // Special cases are:
  //	Logb(±Inf) = +Inf
  //	Logb(0) = -Inf
  //	Logb(NaN) = NaN
  func Logb(x float64) float64 {
  	// special cases
  	switch {
  	case x == 0:
  		return Inf(-1)
  	case IsInf(x, 0):
  		return Inf(1)
  	case IsNaN(x):
  		return x
  	}
  	return float64(ilogb(x))
  }
  
  // Ilogb returns the binary exponent of x as an integer.
  //
  // Special cases are:
  //	Ilogb(±Inf) = MaxInt32
  //	Ilogb(0) = MinInt32
  //	Ilogb(NaN) = MaxInt32
  func Ilogb(x float64) int {
  	// special cases
  	switch {
  	case x == 0:
  		return MinInt32
  	case IsNaN(x):
  		return MaxInt32
  	case IsInf(x, 0):
  		return MaxInt32
  	}
  	return ilogb(x)
  }
  
  // logb returns the binary exponent of x. It assumes x is finite and
  // non-zero.
  func ilogb(x float64) int {
  	x, exp := normalize(x)
  	return int((Float64bits(x)>>shift)&mask) - bias + exp
  }
  

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