1 /*
2 FUNCTION
3 <<div>>---divide two integers
4
5 INDEX
6 div
7
8 SYNOPSIS
9 #include <stdlib.h>
10 div_t div(int <[n]>, int <[d]>);
11
12 DESCRIPTION
13 Divide
14 @tex
15 $n/d$,
16 @end tex
17 @ifnottex
18 <[n]>/<[d]>,
19 @end ifnottex
20 returning quotient and remainder as two integers in a structure <<div_t>>.
21
22 RETURNS
23 The result is represented with the structure
24
25 . typedef struct
26 . {
27 . int quot;
28 . int rem;
29 . } div_t;
30
31 where the <<quot>> field represents the quotient, and <<rem>> the
32 remainder. For nonzero <[d]>, if `<<<[r]> = div(<[n]>,<[d]>);>>' then
33 <[n]> equals `<<<[r]>.rem + <[d]>*<[r]>.quot>>'.
34
35 To divide <<long>> rather than <<int>> values, use the similar
36 function <<ldiv>>.
37
38 PORTABILITY
39 <<div>> is ANSI.
40
41 No supporting OS subroutines are required.
42 */
43
44 /*
45 * Copyright (c) 1990 Regents of the University of California.
46 * All rights reserved.
47 *
48 * This code is derived from software contributed to Berkeley by
49 * Chris Torek.
50 *
51 * Redistribution and use in source and binary forms, with or without
52 * modification, are permitted provided that the following conditions
53 * are met:
54 * 1. Redistributions of source code must retain the above copyright
55 * notice, this list of conditions and the following disclaimer.
56 * 2. Redistributions in binary form must reproduce the above copyright
57 * notice, this list of conditions and the following disclaimer in the
58 * documentation and/or other materials provided with the distribution.
59 * 3. Neither the name of the University nor the names of its contributors
60 * may be used to endorse or promote products derived from this software
61 * without specific prior written permission.
62 *
63 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
64 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
65 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
66 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
67 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
68 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
69 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
70 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
71 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
72 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
73 * SUCH DAMAGE.
74 */
75
76 #include <stdlib.h> /* div_t */
77
78 div_t
div(int num,int denom)79 div (int num,
80 int denom)
81 {
82 div_t r;
83
84 r.quot = num / denom;
85 r.rem = num % denom;
86 /*
87 * The ANSI standard says that |r.quot| <= |n/d|, where
88 * n/d is to be computed in infinite precision. In other
89 * words, we should always truncate the quotient towards
90 * 0, never -infinity or +infinity.
91 *
92 * Machine division and remainer may work either way when
93 * one or both of n or d is negative. If only one is
94 * negative and r.quot has been truncated towards -inf,
95 * r.rem will have the same sign as denom and the opposite
96 * sign of num; if both are negative and r.quot has been
97 * truncated towards -inf, r.rem will be positive (will
98 * have the opposite sign of num). These are considered
99 * `wrong'.
100 *
101 * If both are num and denom are positive, r will always
102 * be positive.
103 *
104 * This all boils down to:
105 * if num >= 0, but r.rem < 0, we got the wrong answer.
106 * In that case, to get the right answer, add 1 to r.quot and
107 * subtract denom from r.rem.
108 * if num < 0, but r.rem > 0, we also have the wrong answer.
109 * In this case, to get the right answer, subtract 1 from r.quot and
110 * add denom to r.rem.
111 */
112 if (num >= 0 && r.rem < 0) {
113 ++r.quot;
114 r.rem -= denom;
115 }
116 else if (num < 0 && r.rem > 0) {
117 --r.quot;
118 r.rem += denom;
119 }
120 return (r);
121 }
122
