_D_cplx_div.c revision 7c478bd95313f5f23a4c958a745db2134aa03244
/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License, Version 1.0 only
* (the "License"). You may not use this file except in compliance
* with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright 2004 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms.
*/
#pragma ident "%Z%%M% %I% %E% SMI"
/*
* _D_cplx_div(z, w) returns z / w with infinities handled according
* to C99.
*
* If z and w are both finite and w is nonzero, _D_cplx_div(z, w)
* delivers the complex quotient q according to the usual formula:
* let a = Re(z), b = Im(z), c = Re(w), and d = Im(w); then q = x +
* I * y where x = (a * c + b * d) / r and y = (b * c - a * d) / r
* with r = c * c + d * d. This implementation computes intermediate
* results in extended precision to avoid premature underflow or over-
* flow.
*
* If z is neither NaN nor zero and w is zero, or if z is infinite
* and w is finite and nonzero, _D_cplx_div delivers an infinite
* result. If z is finite and w is infinite, _D_cplx_div delivers
* a zero result.
*
* If z and w are both zero or both infinite, or if either z or w is
* a complex NaN, _D_cplx_div delivers NaN + I * NaN. C99 doesn't
* specify these cases.
*
* This implementation can raise spurious invalid operation, inexact,
* and division-by-zero exceptions. C99 allows this.
*
* Warning: Do not attempt to "optimize" this code by removing multi-
* plications by zero.
*/
#endif
static union {
int i;
float f;
} inf = {
0x7f800000
};
/*
* Return +1 if x is +Inf, -1 if x is -Inf, and 0 otherwise
*/
static int
testinf(double x)
{
union {
int i[2];
double d;
} xx;
xx.d = x;
}
double _Complex
_D_cplx_div(double _Complex z, double _Complex w)
{
double _Complex v;
union {
int i[2];
double d;
double a, b, c, d;
long double r, x, y;
int i, j, recalc;
/*
* The following is equivalent to
*
* a = creal(z); b = cimag(z);
* c = creal(w); d = cimag(w);
*/
/* LINTED alignment */
a = ((double *)&z)[0];
/* LINTED alignment */
b = ((double *)&z)[1];
/* LINTED alignment */
c = ((double *)&w)[0];
/* LINTED alignment */
d = ((double *)&w)[1];
r = (long double)c * c + (long double)d * d;
if (r == 0.0f) {
/* w is zero; multiply z by 1/Re(w) - I * Im(w) */
c = 1.0f / c;
i = testinf(a);
j = testinf(b);
if (i | j) { /* z is infinite */
a = i;
b = j;
}
/* LINTED alignment */
((double *)&v)[0] = a * c + b * d;
/* LINTED alignment */
((double *)&v)[1] = b * c - a * d;
return (v);
}
r = 1.0f / r;
x = ((long double)a * c + (long double)b * d) * r;
y = ((long double)b * c - (long double)a * d) * r;
if (x != x && y != y) {
/*
* Both x and y are NaN, so z and w can't both be finite
* and nonzero. Since we handled the case w = 0 above,
* the only cases to check here are when one of z or w
* is infinite.
*/
r = 1.0f;
recalc = 0;
i = testinf(a);
j = testinf(b);
if (i | j) { /* z is infinite */
/* "factor out" infinity */
a = i;
b = j;
r = inf.f;
recalc = 1;
}
i = testinf(c);
j = testinf(d);
if (i | j) { /* w is infinite */
/*
* "factor out" infinity, being careful to preserve
* signs of finite values
*/
cc.d = c;
dd.d = d;
r *= 0.0f;
recalc = 1;
}
if (recalc) {
x = ((long double)a * c + (long double)b * d) * r;
y = ((long double)b * c - (long double)a * d) * r;
}
}
/*
* The following is equivalent to
*
* return x + I * y;
*/
/* LINTED alignment */
((double *)&v)[0] = (double)x;
/* LINTED alignment */
((double *)&v)[1] = (double)y;
return (v);
}