/usr/share/go-1.8/src/math/logb.go is in golang-1.8-src 1.8.3-2ubuntu1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 | // 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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