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