100 lines
2.6 KiB
C
100 lines
2.6 KiB
C
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/* $NetBSD: csqrt.c,v 1.1 2007/08/20 16:01:37 drochner Exp $ */
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/*-
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* Copyright (c) 2007 The NetBSD Foundation, Inc.
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* All rights reserved.
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*
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* This code is derived from software written by Stephen L. Moshier.
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* It is redistributed by the NetBSD Foundation by permission of the author.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <complex.h>
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#include <math.h>
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double complex
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csqrt(double complex z)
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{
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double complex w;
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double x, y, r, t, scale;
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x = creal (z);
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y = cimag (z);
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if (y == 0.0) {
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if (x == 0.0) {
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w = 0.0 + y * I;
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} else {
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r = fabs(x);
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r = sqrt(r);
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if (x < 0.0) {
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w = 0.0 + r * I;
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} else {
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w = r + y * I;
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}
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}
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return w;
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}
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if (x == 0.0) {
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r = fabs(y);
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r = sqrt(0.5 * r);
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if (y > 0)
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w = r + r * I;
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else
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w = r - r * I;
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return w;
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}
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/* Rescale to avoid internal overflow or underflow. */
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if ((fabs(x) > 4.0) || (fabs(y) > 4.0)) {
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x *= 0.25;
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y *= 0.25;
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scale = 2.0;
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} else {
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#if 1
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x *= 1.8014398509481984e16; /* 2^54 */
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y *= 1.8014398509481984e16;
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scale = 7.450580596923828125e-9; /* 2^-27 */
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#else
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x *= 4.0;
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y *= 4.0;
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scale = 0.5;
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#endif
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}
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w = x + y * I;
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r = cabs(w);
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if (x > 0) {
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t = sqrt(0.5 * r + 0.5 * x);
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r = scale * fabs((0.5 * y) / t );
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t *= scale;
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} else {
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r = sqrt(0.5 * r - 0.5 * x);
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t = scale * fabs((0.5 * y) / r);
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r *= scale;
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}
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if (y < 0)
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w = t - r * I;
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else
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w = t + r * I;
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return w;
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}
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