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
5package math
6
7// Logb returns the binary exponent of x.
8//
9// Special cases are:
10//	Logb(±Inf) = +Inf
11//	Logb(0) = -Inf
12//	Logb(NaN) = NaN
13func 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 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
32func 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.
47func ilogb(x float64) int {
48	x, exp := normalize(x)
49	return int((Float64bits(x)>>shift)&mask) - bias + exp
50}
51