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div.c revision 1.5 
      1 /*	$NetBSD: div.c,v 1.5 1997/07/13 20:16:40 christos Exp $	*/
      2 
      3 /*
      4  * Copyright (c) 1990 Regents of the University of California.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to Berkeley by
      8  * Chris Torek.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  * 3. All advertising materials mentioning features or use of this software
     19  *    must display the following acknowledgement:
     20  *	This product includes software developed by the University of
     21  *	California, Berkeley and its contributors.
     22  * 4. Neither the name of the University nor the names of its contributors
     23  *    may be used to endorse or promote products derived from this software
     24  *    without specific prior written permission.
     25  *
     26  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     27  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     28  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     29  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     30  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     31  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     32  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     33  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     34  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     35  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     36  * SUCH DAMAGE.
     37  */
     38 
     39 #include <sys/cdefs.h>
     40 #if defined(LIBC_SCCS) && !defined(lint)
     41 #if 0
     42 static char *sccsid = "from: @(#)div.c	5.2 (Berkeley) 4/16/91";
     43 #else
     44 __RCSID("$NetBSD: div.c,v 1.5 1997/07/13 20:16:40 christos Exp $");
     45 #endif
     46 #endif /* LIBC_SCCS and not lint */
     47 
     48 #include <stdlib.h>		/* div_t */
     49 
     50 div_t
     51 div(num, denom)
     52 	int num, denom;
     53 {
     54 	div_t r;
     55 
     56 	r.quot = num / denom;
     57 	r.rem = num % denom;
     58 	/*
     59 	 * The ANSI standard says that |r.quot| <= |n/d|, where
     60 	 * n/d is to be computed in infinite precision.  In other
     61 	 * words, we should always truncate the quotient towards
     62 	 * 0, never -infinity.
     63 	 *
     64 	 * Machine division and remainer may work either way when
     65 	 * one or both of n or d is negative.  If only one is
     66 	 * negative and r.quot has been truncated towards -inf,
     67 	 * r.rem will have the same sign as denom and the opposite
     68 	 * sign of num; if both are negative and r.quot has been
     69 	 * truncated towards -inf, r.rem will be positive (will
     70 	 * have the opposite sign of num).  These are considered
     71 	 * `wrong'.
     72 	 *
     73 	 * If both are num and denom are positive, r will always
     74 	 * be positive.
     75 	 *
     76 	 * This all boils down to:
     77 	 *	if num >= 0, but r.rem < 0, we got the wrong answer.
     78 	 * In that case, to get the right answer, add 1 to r.quot and
     79 	 * subtract denom from r.rem.
     80 	 */
     81 	if (num >= 0 && r.rem < 0) {
     82 		r.quot++;
     83 		r.rem -= denom;
     84 	}
     85 	return (r);
     86 }
     87