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		// TODO(rsc): Remove manual inlining of IsNaN, IsInf
    15		// when compiler does it for us
    16		// special cases
    17		switch {
    18		case x == 0:
    19			return Inf(-1)
    20		case x < -MaxFloat64 || x > MaxFloat64: // IsInf(x, 0):
    21			return Inf(1)
    22		case x != x: // IsNaN(x):
    23			return x
    24		}
    25		return float64(ilogb(x))
    26	}
    27	
    28	// Ilogb(x) returns the binary exponent of x as an integer.
    29	//
    30	// Special cases are:
    31	//	Ilogb(±Inf) = MaxInt32
    32	//	Ilogb(0) = MinInt32
    33	//	Ilogb(NaN) = MaxInt32
    34	func Ilogb(x float64) int {
    35		// TODO(rsc): Remove manual inlining of IsNaN, IsInf
    36		// when compiler does it for us
    37		// special cases
    38		switch {
    39		case x == 0:
    40			return MinInt32
    41		case x != x: // IsNaN(x):
    42			return MaxInt32
    43		case x < -MaxFloat64 || x > MaxFloat64: // IsInf(x, 0):
    44			return MaxInt32
    45		}
    46		return ilogb(x)
    47	}
    48	
    49	// logb returns the binary exponent of x. It assumes x is finite and
    50	// non-zero.
    51	func ilogb(x float64) int {
    52		x, exp := normalize(x)
    53		return int((Float64bits(x)>>shift)&mask) - bias + exp
    54	}
The Go Programming Language

Source file src/pkg/math/logb.go
