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      1 /*	$NetBSD: n_fmod.c,v 1.11 2018/11/09 10:19:47 martin 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 __weak_alias(modfl, fmod);
     74 #endif
     75 #endif
     76 
     77 #ifdef TEST_FMOD
     78 static double
     79 _fmod(double x, double y)
     80 #else	/* TEST_FMOD */
     81 double
     82 fmod(double x, double y)
     83 #endif	/* TEST_FMOD */
     84 {
     85 	int ir,iy;
     86 	double r,w;
     87 
     88 	if (y == (double)0
     89 #if !defined(__vax__) && !defined(tahoe)	/* per "fmod" manual entry, SunOS 4.0 */
     90 		|| isnan(y) || !finite(x)
     91 #endif	/* !defined(__vax__) && !defined(tahoe) */
     92 	    )
     93 	    return (x*y)/(x*y);
     94 
     95 	r = fabs(x);
     96 	y = fabs(y);
     97 	(void)frexp(y,&iy);
     98 	while (r >= y) {
     99 		(void)frexp(r,&ir);
    100 		w = ldexp(y,ir-iy);
    101 		r -= w <= r ? w : w*(double)0.5;
    102 	}
    103 	return x >= (double)0 ? r : -r;
    104 }
    105 
    106 float
    107 fmodf(float x, float y)
    108 {
    109 	return fmod(x, y);
    110 }
    111 
    112 #ifdef TEST_FMOD
    113 #include <math.h>
    114 #include <stdio.h>
    115 #include <stdlib.h>
    116 
    117 #define	NTEST	10000
    118 #define	NCASES	3
    119 
    120 static int nfail = 0;
    121 static void
    122 prf(const char *s, double d)
    123 {
    124 	union {
    125 		double d;
    126 		unsigned long long u;
    127 	} x;
    128 	x.d = d;
    129 	printf("%s = %#016.16llx (%24.16e)\n", s, x.u, x.d);
    130 }
    131 
    132 static void
    133 doit(double x, double y)
    134 {
    135 	double ro = fmod(x,y),rn = _fmod(x,y);
    136 	if (ro != rn) {
    137 		prf(" x   ", x);
    138 		prf(" y   ", y);
    139 		prf(" fmod", ro);
    140 		prf("_fmod", rn);
    141 		(void)printf("\n");
    142 	}
    143 }
    144 
    145 int
    146 main(int argc, char **argv)
    147 {
    148 	int i,cases;
    149 	double x,y;
    150 
    151 	srandom(12345);
    152 	for (i = 0; i < NTEST; i++) {
    153 		x = (double)random();
    154 		y = (double)random();
    155 		for (cases = 0; cases < NCASES; cases++) {
    156 			switch (cases) {
    157 			case 0:
    158 				break;
    159 			case 1:
    160 				y = (double)1/y; break;
    161 			case 2:
    162 				x = (double)1/x; break;
    163 			default:
    164 				abort(); break;
    165 			}
    166 			doit(x,y);
    167 			doit(x,-y);
    168 			doit(-x,y);
    169 			doit(-x,-y);
    170 		}
    171 	}
    172 	if (nfail)
    173 		(void)printf("Number of failures: %d (out of a total of %d)\n",
    174 			nfail,NTEST*NCASES*4);
    175 	else
    176 		(void)printf("No discrepancies were found\n");
    177 	exit(0);
    178 }
    179 #endif	/* TEST_FMOD */
    180