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n_fmod.c revision 1.10 
      1 /*	$NetBSD: n_fmod.c,v 1.10 2016/01/16 21:31:38 christos 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 #if DBL_MANT_DIG == LDBL_MANT_DIG && DBL_MIN_EXP == LDBL_MIN_EXP \
     70 	 && DBL_MIN_EXP == LDBL_MIN_EXP
     71 #ifdef __weak_alias
     72 __weak_alias(fmodl, fmod);
     73 #endif
     74 #endif
     75 
     76 #ifdef TEST_FMOD
     77 static double
     78 _fmod(double x, double y)
     79 #else	/* TEST_FMOD */
     80 double
     81 fmod(double x, double y)
     82 #endif	/* TEST_FMOD */
     83 {
     84 	int ir,iy;
     85 	double r,w;
     86 
     87 	if (y == (double)0
     88 #if !defined(__vax__) && !defined(tahoe)	/* per "fmod" manual entry, SunOS 4.0 */
     89 		|| isnan(y) || !finite(x)
     90 #endif	/* !defined(__vax__) && !defined(tahoe) */
     91 	    )
     92 	    return (x*y)/(x*y);
     93 
     94 	r = fabs(x);
     95 	y = fabs(y);
     96 	(void)frexp(y,&iy);
     97 	while (r >= y) {
     98 		(void)frexp(r,&ir);
     99 		w = ldexp(y,ir-iy);
    100 		r -= w <= r ? w : w*(double)0.5;
    101 	}
    102 	return x >= (double)0 ? r : -r;
    103 }
    104 
    105 float
    106 fmodf(float x, float y)
    107 {
    108 	return fmod(x, y);
    109 }
    110 
    111 #ifdef TEST_FMOD
    112 #include <math.h>
    113 #include <stdio.h>
    114 #include <stdlib.h>
    115 
    116 #define	NTEST	10000
    117 #define	NCASES	3
    118 
    119 static int nfail = 0;
    120 static void
    121 prf(const char *s, double d)
    122 {
    123 	union {
    124 		double d;
    125 		unsigned long long u;
    126 	} x;
    127 	x.d = d;
    128 	printf("%s = %#016.16llx (%24.16e)\n", s, x.u, x.d);
    129 }
    130 
    131 static void
    132 doit(double x, double y)
    133 {
    134 	double ro = fmod(x,y),rn = _fmod(x,y);
    135 	if (ro != rn) {
    136 		prf(" x   ", x);
    137 		prf(" y   ", y);
    138 		prf(" fmod", ro);
    139 		prf("_fmod", rn);
    140 		(void)printf("\n");
    141 	}
    142 }
    143 
    144 int
    145 main(int argc, char **argv)
    146 {
    147 	int i,cases;
    148 	double x,y;
    149 
    150 	srandom(12345);
    151 	for (i = 0; i < NTEST; i++) {
    152 		x = (double)random();
    153 		y = (double)random();
    154 		for (cases = 0; cases < NCASES; cases++) {
    155 			switch (cases) {
    156 			case 0:
    157 				break;
    158 			case 1:
    159 				y = (double)1/y; break;
    160 			case 2:
    161 				x = (double)1/x; break;
    162 			default:
    163 				abort(); break;
    164 			}
    165 			doit(x,y);
    166 			doit(x,-y);
    167 			doit(-x,y);
    168 			doit(-x,-y);
    169 		}
    170 	}
    171 	if (nfail)
    172 		(void)printf("Number of failures: %d (out of a total of %d)\n",
    173 			nfail,NTEST*NCASES*4);
    174 	else
    175 		(void)printf("No discrepancies were found\n");
    176 	exit(0);
    177 }
    178 #endif	/* TEST_FMOD */
    179