1 /* $OpenBSD: div.c,v 1.6 2015/09/13 08:31:47 guenther Exp $ */
2 /*
3 * Copyright (c) 1990 Regents of the University of California.
4 * All rights reserved.
5 *
6 * This code is derived from software contributed to Berkeley by
7 * Chris Torek.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
17 * 3. Neither the name of the University nor the names of its contributors
18 * may be used to endorse or promote products derived from this software
19 * without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 */
33
34 #include <stdlib.h> /* div_t */
35
36 div_t
div(int num,int denom)37 div(int num, int denom)
38 {
39 div_t r;
40
41 r.quot = num / denom;
42 r.rem = num % denom;
43 /*
44 * The ANSI standard says that |r.quot| <= |n/d|, where
45 * n/d is to be computed in infinite precision. In other
46 * words, we should always truncate the quotient towards
47 * 0, never -infinity.
48 *
49 * Machine division and remainer may work either way when
50 * one or both of n or d is negative. If only one is
51 * negative and r.quot has been truncated towards -inf,
52 * r.rem will have the same sign as denom and the opposite
53 * sign of num; if both are negative and r.quot has been
54 * truncated towards -inf, r.rem will be positive (will
55 * have the opposite sign of num). These are considered
56 * `wrong'.
57 *
58 * If both are num and denom are positive, r will always
59 * be positive.
60 *
61 * This all boils down to:
62 * if num >= 0, but r.rem < 0, we got the wrong answer.
63 * In that case, to get the right answer, add 1 to r.quot and
64 * subtract denom from r.rem.
65 */
66 if (num >= 0 && r.rem < 0) {
67 r.quot++;
68 r.rem -= denom;
69 }
70 return (r);
71 }
72 DEF_STRONG(div);
73