xref: /minix3/lib/libm/complex/csqrtf.c (revision 2fe8fb192fe7e8720e3e7a77f928da545e872a6a)
1 /* $NetBSD: csqrtf.c,v 1.1 2007/08/20 16:01:37 drochner Exp $ */
2 
3 /*-
4  * Copyright (c) 2007 The NetBSD Foundation, Inc.
5  * All rights reserved.
6  *
7  * This code is derived from software written by Stephen L. Moshier.
8  * It is redistributed by the NetBSD Foundation by permission of the author.
9  *
10  * Redistribution and use in source and binary forms, with or without
11  * modification, are permitted provided that the following conditions
12  * are met:
13  * 1. Redistributions of source code must retain the above copyright
14  *    notice, this list of conditions and the following disclaimer.
15  * 2. Redistributions in binary form must reproduce the above copyright
16  *    notice, this list of conditions and the following disclaimer in the
17  *    documentation and/or other materials provided with the distribution.
18  *
19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
29  * POSSIBILITY OF SUCH DAMAGE.
30  */
31 
32 #include <complex.h>
33 #include <math.h>
34 
35 float complex
csqrtf(float complex z)36 csqrtf(float complex z)
37 {
38 	float complex w;
39 	float x, y, r, t, scale;
40 
41 	x = crealf (z);
42 	y = cimagf (z);
43 
44 	if (y == 0.0f) {
45 		if (x < 0.0f) {
46 			w = 0.0f + sqrtf(-x) * I;
47 			return w;
48 		} else if (x == 0.0f) {
49 			return (0.0f + y * I);
50 		} else {
51 			w = sqrtf(x) + y * I;
52 			return w;
53 		}
54 	}
55 
56 	if (x == 0.0f) {
57 		r = fabsf(y);
58 		r = sqrtf(0.5f * r);
59 		if (y > 0)
60 			w = r + r * I;
61 		else
62 			w = r - r * I;
63 		return w;
64 	}
65 
66 	/* Rescale to avoid internal overflow or underflow.  */
67 	if ((fabsf(x) > 4.0f) || (fabsf(y) > 4.0f)) {
68 		x *= 0.25f;
69 		y *= 0.25f;
70 		scale = 2.0f;
71 	} else {
72 #if 1
73 		x *= 6.7108864e7f; /* 2^26 */
74 		y *= 6.7108864e7f;
75 		scale = 1.220703125e-4f; /* 2^-13 */
76 #else
77 		x *= 4.0f;
78 		y *= 4.0f;
79 		scale = 0.5f;
80 #endif
81 	}
82 	w = x + y * I;
83 	r = cabsf(w);
84 	if( x > 0 ) {
85 		t = sqrtf(0.5f * r + 0.5f * x);
86 		r = scale * fabsf((0.5f * y) / t);
87 		t *= scale;
88 	} else {
89 		r = sqrtf(0.5f * r - 0.5f * x);
90 		t = scale * fabsf((0.5f * y) / r);
91 		r *= scale;
92 	}
93 
94 	if (y < 0)
95 		w = t - r * I;
96 	else
97 		w = t + r * I;
98 	return w;
99 }
100