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 }