1// Copyright 2009 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
7const (
8	uvnan    = 0x7FF8000000000001
9	uvinf    = 0x7FF0000000000000
10	uvneginf = 0xFFF0000000000000
11	uvone    = 0x3FF0000000000000
12	mask     = 0x7FF
13	shift    = 64 - 11 - 1
14	bias     = 1023
15	signMask = 1 << 63
16	fracMask = 1<<shift - 1
17)
18
19// Inf returns positive infinity if sign >= 0, negative infinity if sign < 0.
20func Inf(sign int) float64 {
21	var v uint64
22	if sign >= 0 {
23		v = uvinf
24	} else {
25		v = uvneginf
26	}
27	return Float64frombits(v)
28}
29
30// NaN returns an IEEE 754 “not-a-number” value.
31func NaN() float64 { return Float64frombits(uvnan) }
32
33// IsNaN reports whether f is an IEEE 754 “not-a-number” value.
34func IsNaN(f float64) (is bool) {
35	// IEEE 754 says that only NaNs satisfy f != f.
36	// To avoid the floating-point hardware, could use:
37	//	x := Float64bits(f);
38	//	return uint32(x>>shift)&mask == mask && x != uvinf && x != uvneginf
39	return f != f
40}
41
42// IsInf reports whether f is an infinity, according to sign.
43// If sign > 0, IsInf reports whether f is positive infinity.
44// If sign < 0, IsInf reports whether f is negative infinity.
45// If sign == 0, IsInf reports whether f is either infinity.
46func IsInf(f float64, sign int) bool {
47	// Test for infinity by comparing against maximum float.
48	// To avoid the floating-point hardware, could use:
49	//	x := Float64bits(f);
50	//	return sign >= 0 && x == uvinf || sign <= 0 && x == uvneginf;
51	return sign >= 0 && f > MaxFloat64 || sign <= 0 && f < -MaxFloat64
52}
53
54// normalize returns a normal number y and exponent exp
55// satisfying x == y × 2**exp. It assumes x is finite and non-zero.
56func normalize(x float64) (y float64, exp int) {
57	const SmallestNormal = 2.2250738585072014e-308 // 2**-1022
58	if Abs(x) < SmallestNormal {
59		return x * (1 << 52), -52
60	}
61	return x, 0
62}
63