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