div.c revision 92986 
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. 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)
38static char sccsid[] = "@(#)div.c	8.1 (Berkeley) 6/4/93";
39#endif /* LIBC_SCCS and not lint */
40#include <sys/cdefs.h>
41__FBSDID("$FreeBSD: head/lib/libc/stdlib/div.c 92986 2002-03-22 21:53:29Z obrien $");
42
43#include <stdlib.h>		/* div_t */
44
45div_t
46div(num, denom)
47	int num, denom;
48{
49	div_t r;
50
51	r.quot = num / denom;
52	r.rem = num % denom;
53	/*
54	 * The ANSI standard says that |r.quot| <= |n/d|, where
55	 * n/d is to be computed in infinite precision.  In other
56	 * words, we should always truncate the quotient towards
57	 * 0, never -infinity.
58	 *
59	 * Machine division and remainer may work either way when
60	 * one or both of n or d is negative.  If only one is
61	 * negative and r.quot has been truncated towards -inf,
62	 * r.rem will have the same sign as denom and the opposite
63	 * sign of num; if both are negative and r.quot has been
64	 * truncated towards -inf, r.rem will be positive (will
65	 * have the opposite sign of num).  These are considered
66	 * `wrong'.
67	 *
68	 * If both are num and denom are positive, r will always
69	 * be positive.
70	 *
71	 * This all boils down to:
72	 *	if num >= 0, but r.rem < 0, we got the wrong answer.
73	 * In that case, to get the right answer, add 1 to r.quot and
74	 * subtract denom from r.rem.
75	 */
76	if (num >= 0 && r.rem < 0) {
77		r.quot++;
78		r.rem -= denom;
79	}
80	return (r);
81}
82