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n_fmod.c revision 1.5 
      1 /*	$NetBSD: n_fmod.c,v 1.5 2003/08/07 16:44:51 agc 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. Neither the name of the University nor the names of its contributors
     15  *    may be used to endorse or promote products derived from this software
     16  *    without specific prior written permission.
     17  *
     18  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     19  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     20  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     21  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     22  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     23  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     24  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     25  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     26  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     27  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     28  * SUCH DAMAGE.
     29  */
     30 
     31 #ifndef lint
     32 #if 0
     33 static char sccsid[] = "@(#)fmod.c	8.1 (Berkeley) 6/4/93";
     34 #endif
     35 #endif /* not lint */
     36 
     37 #include "mathimpl.h"
     38 
     39 /* fmod.c
     40  *
     41  * SYNOPSIS
     42  *
     43  *    #include <math.h>
     44  *    double fmod(double x, double y)
     45  *
     46  * DESCRIPTION
     47  *
     48  *    The fmod function computes the floating-point remainder of x/y.
     49  *
     50  * RETURNS
     51  *
     52  *    The fmod function returns the value x-i*y, for some integer i
     53  * such that, if y is nonzero, the result has the same sign as x and
     54  * magnitude less than the magnitude of y.
     55  *
     56  * On a VAX or CCI,
     57  *
     58  *    fmod(x,0) traps/faults on floating-point divided-by-zero.
     59  *
     60  * On IEEE-754 conforming machines with "isnan()" primitive,
     61  *
     62  *    fmod(x,0), fmod(INF,y) are invalid operations and NaN is returned.
     63  *
     64  */
     65 #if !defined(__vax__) && !defined(tahoe)
     66 extern int isnan(),finite();
     67 #endif	/* !defined(__vax__) && !defined(tahoe) */
     68 
     69 #ifdef TEST_FMOD
     70 static double
     71 _fmod(double x, double y)
     72 #else	/* TEST_FMOD */
     73 double
     74 fmod(double x, double y)
     75 #endif	/* TEST_FMOD */
     76 {
     77 	int ir,iy;
     78 	double r,w;
     79 
     80 	if (y == (double)0
     81 #if !defined(__vax__) && !defined(tahoe)	/* per "fmod" manual entry, SunOS 4.0 */
     82 		|| isnan(y) || !finite(x)
     83 #endif	/* !defined(__vax__) && !defined(tahoe) */
     84 	    )
     85 	    return (x*y)/(x*y);
     86 
     87 	r = fabs(x);
     88 	y = fabs(y);
     89 	(void)frexp(y,&iy);
     90 	while (r >= y) {
     91 		(void)frexp(r,&ir);
     92 		w = ldexp(y,ir-iy);
     93 		r -= w <= r ? w : w*(double)0.5;
     94 	}
     95 	return x >= (double)0 ? r : -r;
     96 }
     97 
     98 #ifdef TEST_FMOD
     99 extern long random();
    100 extern double fmod();
    101 
    102 #define	NTEST	10000
    103 #define	NCASES	3
    104 
    105 static int nfail = 0;
    106 
    107 static void
    108 doit(double x, double y)
    109 {
    110 	double ro = fmod(x,y),rn = _fmod(x,y);
    111 	if (ro != rn) {
    112 		(void)printf(" x    = 0x%08.8x %08.8x (%24.16e)\n",x,x);
    113 		(void)printf(" y    = 0x%08.8x %08.8x (%24.16e)\n",y,y);
    114 		(void)printf(" fmod = 0x%08.8x %08.8x (%24.16e)\n",ro,ro);
    115 		(void)printf("_fmod = 0x%08.8x %08.8x (%24.16e)\n",rn,rn);
    116 		(void)printf("\n");
    117 	}
    118 }
    119 
    120 int
    121 main(int argc, char **argv)
    122 {
    123 	int i,cases;
    124 	double x,y;
    125 
    126 	srandom(12345);
    127 	for (i = 0; i < NTEST; i++) {
    128 		x = (double)random();
    129 		y = (double)random();
    130 		for (cases = 0; cases < NCASES; cases++) {
    131 			switch (cases) {
    132 			case 0:
    133 				break;
    134 			case 1:
    135 				y = (double)1/y; break;
    136 			case 2:
    137 				x = (double)1/x; break;
    138 			default:
    139 				abort(); break;
    140 			}
    141 			doit(x,y);
    142 			doit(x,-y);
    143 			doit(-x,y);
    144 			doit(-x,-y);
    145 		}
    146 	}
    147 	if (nfail)
    148 		(void)printf("Number of failures: %d (out of a total of %d)\n",
    149 			nfail,NTEST*NCASES*4);
    150 	else
    151 		(void)printf("No discrepancies were found\n");
    152 	exit(0);
    153 }
    154 #endif	/* TEST_FMOD */
    155