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n_fmod.c revision 1.3 
      1 /*	$NetBSD: n_fmod.c,v 1.3 1998/10/20 02:26:11 matt Exp $	*/
      2 /*
      3  * Copyright (c) 1989, 1993
      4  *	The Regents of the University of California.  All rights reserved.
      5  *
      6  * Redistribution and use in source and binary forms, with or without
      7  * modification, are permitted provided that the following conditions
      8  * are met:
      9  * 1. Redistributions of source code must retain the above copyright
     10  *    notice, this list of conditions and the following disclaimer.
     11  * 2. Redistributions in binary form must reproduce the above copyright
     12  *    notice, this list of conditions and the following disclaimer in the
     13  *    documentation and/or other materials provided with the distribution.
     14  * 3. All advertising materials mentioning features or use of this software
     15  *    must display the following acknowledgement:
     16  *	This product includes software developed by the University of
     17  *	California, Berkeley and its contributors.
     18  * 4. Neither the name of the University nor the names of its contributors
     19  *    may be used to endorse or promote products derived from this software
     20  *    without specific prior written permission.
     21  *
     22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     32  * SUCH DAMAGE.
     33  */
     34 
     35 #ifndef lint
     36 #if 0
     37 static char sccsid[] = "@(#)fmod.c	8.1 (Berkeley) 6/4/93";
     38 #endif
     39 #endif /* not lint */
     40 
     41 #include "mathimpl.h"
     42 
     43 /* fmod.c
     44  *
     45  * SYNOPSIS
     46  *
     47  *    #include <math.h>
     48  *    double fmod(double x, double y)
     49  *
     50  * DESCRIPTION
     51  *
     52  *    The fmod function computes the floating-point remainder of x/y.
     53  *
     54  * RETURNS
     55  *
     56  *    The fmod function returns the value x-i*y, for some integer i
     57  * such that, if y is nonzero, the result has the same sign as x and
     58  * magnitude less than the magnitude of y.
     59  *
     60  * On a VAX or CCI,
     61  *
     62  *    fmod(x,0) traps/faults on floating-point divided-by-zero.
     63  *
     64  * On IEEE-754 conforming machines with "isnan()" primitive,
     65  *
     66  *    fmod(x,0), fmod(INF,y) are invalid operations and NaN is returned.
     67  *
     68  */
     69 #if !defined(__vax__) && !defined(tahoe)
     70 extern int isnan(),finite();
     71 #endif	/* !defined(__vax__) && !defined(tahoe) */
     72 
     73 #ifdef TEST_FMOD
     74 static double
     75 _fmod(x,y)
     76 #else	/* TEST_FMOD */
     77 double
     78 fmod(x,y)
     79 #endif	/* TEST_FMOD */
     80 double x,y;
     81 {
     82 	int ir,iy;
     83 	double r,w;
     84 
     85 	if (y == (double)0
     86 #if !defined(__vax__) && !defined(tahoe)	/* per "fmod" manual entry, SunOS 4.0 */
     87 		|| isnan(y) || !finite(x)
     88 #endif	/* !defined(__vax__) && !defined(tahoe) */
     89 	    )
     90 	    return (x*y)/(x*y);
     91 
     92 	r = fabs(x);
     93 	y = fabs(y);
     94 	(void)frexp(y,&iy);
     95 	while (r >= y) {
     96 		(void)frexp(r,&ir);
     97 		w = ldexp(y,ir-iy);
     98 		r -= w <= r ? w : w*(double)0.5;
     99 	}
    100 	return x >= (double)0 ? r : -r;
    101 }
    102 
    103 #ifdef TEST_FMOD
    104 extern long random();
    105 extern double fmod();
    106 
    107 #define	NTEST	10000
    108 #define	NCASES	3
    109 
    110 static int nfail = 0;
    111 
    112 static void
    113 doit(x,y)
    114 double x,y;
    115 {
    116 	double ro = fmod(x,y),rn = _fmod(x,y);
    117 	if (ro != rn) {
    118 		(void)printf(" x    = 0x%08.8x %08.8x (%24.16e)\n",x,x);
    119 		(void)printf(" y    = 0x%08.8x %08.8x (%24.16e)\n",y,y);
    120 		(void)printf(" fmod = 0x%08.8x %08.8x (%24.16e)\n",ro,ro);
    121 		(void)printf("_fmod = 0x%08.8x %08.8x (%24.16e)\n",rn,rn);
    122 		(void)printf("\n");
    123 	}
    124 }
    125 
    126 main()
    127 {
    128 	register int i,cases;
    129 	double x,y;
    130 
    131 	srandom(12345);
    132 	for (i = 0; i < NTEST; i++) {
    133 		x = (double)random();
    134 		y = (double)random();
    135 		for (cases = 0; cases < NCASES; cases++) {
    136 			switch (cases) {
    137 			case 0:
    138 				break;
    139 			case 1:
    140 				y = (double)1/y; break;
    141 			case 2:
    142 				x = (double)1/x; break;
    143 			default:
    144 				abort(); break;
    145 			}
    146 			doit(x,y);
    147 			doit(x,-y);
    148 			doit(-x,y);
    149 			doit(-x,-y);
    150 		}
    151 	}
    152 	if (nfail)
    153 		(void)printf("Number of failures: %d (out of a total of %d)\n",
    154 			nfail,NTEST*NCASES*4);
    155 	else
    156 		(void)printf("No discrepancies were found\n");
    157 	exit(0);
    158 }
    159 #endif	/* TEST_FMOD */
    160