usr/src/lib/libm/common_source/fmod.c

/*
 * Copyright (c) 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
 */

#ifndef lint
static char sccsid[] = "@(#)fmod.c      8.1 (Berkeley) 6/4/93";
#endif /* not lint */

/* fmod.c
 *
 * SYNOPSIS
 *
 *    #include <math.h>
 *    double fmod(double x, double y)
 *
 * DESCRIPTION
 *
 *    The fmod function computes the floating-point remainder of x/y.
 *
 * RETURNS
 *
 *    The fmod function returns the value x-i*y, for some integer i
 * such that, if y is nonzero, the result has the same sign as x and
 * magnitude less than the magnitude of y.
 *
 * On a VAX or CCI,
 *
 *    fmod(x,0) traps/faults on floating-point divided-by-zero.
 *
 * On IEEE-754 conforming machines with "isnan()" primitive,
 *
 *    fmod(x,0), fmod(INF,y) are invalid operations and NaN is returned.
 *
 */
#if !defined(vax) && !defined(tahoe)
extern int isnan(),finite();
#endif  /* !defined(vax) && !defined(tahoe) */
extern double frexp(),ldexp(),fabs();

#ifdef TEST_FMOD
static double
_fmod(x,y)
#else   /* TEST_FMOD */
double
fmod(x,y)
#endif  /* TEST_FMOD */
double x,y;
{
        int ir,iy;
        double r,w;

        if (y == (double)0
#if !defined(vax) && !defined(tahoe)    /* per "fmod" manual entry, SunOS 4.0 */
                || isnan(y) || !finite(x)
#endif  /* !defined(vax) && !defined(tahoe) */
            )
            return (x*y)/(x*y);

        r = fabs(x);
        y = fabs(y);
        (void)frexp(y,&iy);
        while (r >= y) {
                (void)frexp(r,&ir);
                w = ldexp(y,ir-iy);
                r -= w <= r ? w : w*(double)0.5;
        }
        return x >= (double)0 ? r : -r;
}

#ifdef TEST_FMOD
extern long random();
extern double fmod();

#define NTEST   10000
#define NCASES  3

static int nfail = 0;

static void
doit(x,y)
double x,y;
{
        double ro = fmod(x,y),rn = _fmod(x,y);
        if (ro != rn) {
                (void)printf(" x    = 0x%08.8x %08.8x (%24.16e)\n",x,x);
                (void)printf(" y    = 0x%08.8x %08.8x (%24.16e)\n",y,y);
                (void)printf(" fmod = 0x%08.8x %08.8x (%24.16e)\n",ro,ro);
                (void)printf("_fmod = 0x%08.8x %08.8x (%24.16e)\n",rn,rn);
                (void)printf("\n");
        }
}

main()
{
        register int i,cases;
        double x,y;

        srandom(12345);
        for (i = 0; i < NTEST; i++) {
                x = (double)random();
                y = (double)random();
                for (cases = 0; cases < NCASES; cases++) {
                        switch (cases) {
                        case 0:
                                break;
                        case 1:
                                y = (double)1/y; break;
                        case 2:
                                x = (double)1/x; break;
                        default:
                                abort(); break;
                        }
                        doit(x,y);
                        doit(x,-y);
                        doit(-x,y);
                        doit(-x,-y);
                }
        }
        if (nfail)
                (void)printf("Number of failures: %d (out of a total of %d)\n",
                        nfail,NTEST*NCASES*4);
        else
                (void)printf("No discrepancies were found\n");
        exit(0);
}
#endif  /* TEST_FMOD */