Source file src/pkg/math/logb.go

     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(x) 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(x) 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	}