div.c revision 251069 
1/*
2 * Copyright (c) 1990, 1993
3 *	The Regents of the University of California.  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. Neither the name of the University nor the names of its contributors
17 *    may be used to endorse or promote products derived from this software
18 *    without specific prior written permission.
19 *
20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30 * SUCH DAMAGE.
31 */
32
33#if defined(LIBC_SCCS) && !defined(lint)
34static char sccsid[] = "@(#)div.c	8.1 (Berkeley) 6/4/93";
35#endif /* LIBC_SCCS and not lint */
36#include <sys/cdefs.h>
37__FBSDID("$FreeBSD: head/lib/libc/stdlib/div.c 251069 2013-05-28 20:57:40Z emaste $");
38
39#include <stdlib.h>		/* div_t */
40
41div_t
42div(num, denom)
43	int num, denom;
44{
45	div_t r;
46
47	r.quot = num / denom;
48	r.rem = num % denom;
49	/*
50	 * The ANSI standard says that |r.quot| <= |n/d|, where
51	 * n/d is to be computed in infinite precision.  In other
52	 * words, we should always truncate the quotient towards
53	 * 0, never -infinity.
54	 *
55	 * Machine division and remainer may work either way when
56	 * one or both of n or d is negative.  If only one is
57	 * negative and r.quot has been truncated towards -inf,
58	 * r.rem will have the same sign as denom and the opposite
59	 * sign of num; if both are negative and r.quot has been
60	 * truncated towards -inf, r.rem will be positive (will
61	 * have the opposite sign of num).  These are considered
62	 * `wrong'.
63	 *
64	 * If both are num and denom are positive, r will always
65	 * be positive.
66	 *
67	 * This all boils down to:
68	 *	if num >= 0, but r.rem < 0, we got the wrong answer.
69	 * In that case, to get the right answer, add 1 to r.quot and
70	 * subtract denom from r.rem.
71	 */
72	if (num >= 0 && r.rem < 0) {
73		r.quot++;
74		r.rem -= denom;
75	}
76	return (r);
77}
78