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div.c revision 1.1 
      1 /*
      2  * Copyright (c) 1990 Regents of the University of California.
      3  * All rights reserved.
      4  *
      5  * This code is derived from software contributed to Berkeley by
      6  * Chris Torek.
      7  *
      8  * Redistribution and use in source and binary forms, with or without
      9  * modification, are permitted provided that the following conditions
     10  * are met:
     11  * 1. Redistributions of source code must retain the above copyright
     12  *    notice, this list of conditions and the following disclaimer.
     13  * 2. Redistributions in binary form must reproduce the above copyright
     14  *    notice, this list of conditions and the following disclaimer in the
     15  *    documentation and/or other materials provided with the distribution.
     16  * 3. All advertising materials mentioning features or use of this software
     17  *    must display the following acknowledgement:
     18  *	This product includes software developed by the University of
     19  *	California, Berkeley and its contributors.
     20  * 4. Neither the name of the University nor the names of its contributors
     21  *    may be used to endorse or promote products derived from this software
     22  *    without specific prior written permission.
     23  *
     24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     34  * SUCH DAMAGE.
     35  */
     36 
     37 #if defined(LIBC_SCCS) && !defined(lint)
     38 static char sccsid[] = "@(#)div.c	5.2 (Berkeley) 4/16/91";
     39 #endif /* LIBC_SCCS and not lint */
     40 
     41 #include <stdlib.h>		/* div_t */
     42 
     43 div_t
     44 div(num, denom)
     45 	int num, denom;
     46 {
     47 	div_t r;
     48 
     49 	r.quot = num / denom;
     50 	r.rem = num % denom;
     51 	/*
     52 	 * The ANSI standard says that |r.quot| <= |n/d|, where
     53 	 * n/d is to be computed in infinite precision.  In other
     54 	 * words, we should always truncate the quotient towards
     55 	 * 0, never -infinity.
     56 	 *
     57 	 * Machine division and remainer may work either way when
     58 	 * one or both of n or d is negative.  If only one is
     59 	 * negative and r.quot has been truncated towards -inf,
     60 	 * r.rem will have the same sign as denom and the opposite
     61 	 * sign of num; if both are negative and r.quot has been
     62 	 * truncated towards -inf, r.rem will be positive (will
     63 	 * have the opposite sign of num).  These are considered
     64 	 * `wrong'.
     65 	 *
     66 	 * If both are num and denom are positive, r will always
     67 	 * be positive.
     68 	 *
     69 	 * This all boils down to:
     70 	 *	if num >= 0, but r.rem < 0, we got the wrong answer.
     71 	 * In that case, to get the right answer, add 1 to r.quot and
     72 	 * subtract denom from r.rem.
     73 	 */
     74 	if (num >= 0 && r.rem < 0) {
     75 		r.quot++;
     76 		r.rem -= denom;
     77 	}
     78 	return (r);
     79 }
     80