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 runtime
6
7// inf2one returns a signed 1 if f is an infinity and a signed 0 otherwise.
8// The sign of the result is the sign of f.
9func inf2one(f float64) float64 {
10	g := 0.0
11	if isInf(f) {
12		g = 1.0
13	}
14	return copysign(g, f)
15}
16
17func complex128div(n complex128, m complex128) complex128 {
18	var e, f float64 // complex(e, f) = n/m
19
20	// Algorithm for robust complex division as described in
21	// Robert L. Smith: Algorithm 116: Complex division. Commun. ACM 5(8): 435 (1962).
22	if abs(real(m)) >= abs(imag(m)) {
23		ratio := imag(m) / real(m)
24		denom := real(m) + ratio*imag(m)
25		e = (real(n) + imag(n)*ratio) / denom
26		f = (imag(n) - real(n)*ratio) / denom
27	} else {
28		ratio := real(m) / imag(m)
29		denom := imag(m) + ratio*real(m)
30		e = (real(n)*ratio + imag(n)) / denom
31		f = (imag(n)*ratio - real(n)) / denom
32	}
33
34	if isNaN(e) && isNaN(f) {
35		// Correct final result to infinities and zeros if applicable.
36		// Matches C99: ISO/IEC 9899:1999 - G.5.1  Multiplicative operators.
37
38		a, b := real(n), imag(n)
39		c, d := real(m), imag(m)
40
41		switch {
42		case m == 0 && (!isNaN(a) || !isNaN(b)):
43			e = copysign(inf, c) * a
44			f = copysign(inf, c) * b
45
46		case (isInf(a) || isInf(b)) && isFinite(c) && isFinite(d):
47			a = inf2one(a)
48			b = inf2one(b)
49			e = inf * (a*c + b*d)
50			f = inf * (b*c - a*d)
51
52		case (isInf(c) || isInf(d)) && isFinite(a) && isFinite(b):
53			c = inf2one(c)
54			d = inf2one(d)
55			e = 0 * (a*c + b*d)
56			f = 0 * (b*c - a*d)
57		}
58	}
59
60	return complex(e, f)
61}
62