1 /*
2 FUNCTION
3 <<div>>---divide two integers
4 
5 INDEX
6 	div
7 
8 ANSI_SYNOPSIS
9 	#include <stdlib.h>
10 	div_t div(int <[n]>, int <[d]>);
11 
12 TRAD_SYNOPSIS
13 	#include <stdlib.h>
14 	div_t div(<[n]>, <[d]>)
15 	int <[n]>, <[d]>;
16 
17 DESCRIPTION
18 Divide
19 @tex
20 $n/d$,
21 @end tex
22 @ifnottex
23 <[n]>/<[d]>,
24 @end ifnottex
25 returning quotient and remainder as two integers in a structure <<div_t>>.
26 
27 RETURNS
28 The result is represented with the structure
29 
30 . typedef struct
31 . {
32 .  int quot;
33 .  int rem;
34 . } div_t;
35 
36 where the <<quot>> field represents the quotient, and <<rem>> the
37 remainder.  For nonzero <[d]>, if `<<<[r]> = div(<[n]>,<[d]>);>>' then
38 <[n]> equals `<<<[r]>.rem + <[d]>*<[r]>.quot>>'.
39 
40 To divide <<long>> rather than <<int>> values, use the similar
41 function <<ldiv>>.
42 
43 PORTABILITY
44 <<div>> is ANSI.
45 
46 No supporting OS subroutines are required.
47 */
48 
49 /*
50  * Copyright (c) 1990 Regents of the University of California.
51  * All rights reserved.
52  *
53  * This code is derived from software contributed to Berkeley by
54  * Chris Torek.
55  *
56  * Redistribution and use in source and binary forms, with or without
57  * modification, are permitted provided that the following conditions
58  * are met:
59  * 1. Redistributions of source code must retain the above copyright
60  *    notice, this list of conditions and the following disclaimer.
61  * 2. Redistributions in binary form must reproduce the above copyright
62  *    notice, this list of conditions and the following disclaimer in the
63  *    documentation and/or other materials provided with the distribution.
64  * 3. All advertising materials mentioning features or use of this software
65  *    must display the following acknowledgement:
66  *	This product includes software developed by the University of
67  *	California, Berkeley and its contributors.
68  * 4. Neither the name of the University nor the names of its contributors
69  *    may be used to endorse or promote products derived from this software
70  *    without specific prior written permission.
71  *
72  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
73  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
74  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
75  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
76  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
77  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
78  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
79  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
80  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
81  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
82  * SUCH DAMAGE.
83  */
84 
85 #include <_ansi.h>
86 #include <stdlib.h>		/* div_t */
87 
88 div_t
89 _DEFUN (div, (num, denom),
90 	int num _AND
91 	int denom)
92 {
93 	div_t r;
94 
95 	r.quot = num / denom;
96 	r.rem = num % denom;
97 	/*
98 	 * The ANSI standard says that |r.quot| <= |n/d|, where
99 	 * n/d is to be computed in infinite precision.  In other
100 	 * words, we should always truncate the quotient towards
101 	 * 0, never -infinity or +infinity.
102 	 *
103 	 * Machine division and remainer may work either way when
104 	 * one or both of n or d is negative.  If only one is
105 	 * negative and r.quot has been truncated towards -inf,
106 	 * r.rem will have the same sign as denom and the opposite
107 	 * sign of num; if both are negative and r.quot has been
108 	 * truncated towards -inf, r.rem will be positive (will
109 	 * have the opposite sign of num).  These are considered
110 	 * `wrong'.
111 	 *
112 	 * If both are num and denom are positive, r will always
113 	 * be positive.
114 	 *
115 	 * This all boils down to:
116 	 *	if num >= 0, but r.rem < 0, we got the wrong answer.
117 	 * In that case, to get the right answer, add 1 to r.quot and
118 	 * subtract denom from r.rem.
119 	 *      if num < 0, but r.rem > 0, we also have the wrong answer.
120 	 * In this case, to get the right answer, subtract 1 from r.quot and
121 	 * add denom to r.rem.
122 	 */
123 	if (num >= 0 && r.rem < 0) {
124 		++r.quot;
125 		r.rem -= denom;
126 	}
127 	else if (num < 0 && r.rem > 0) {
128 		--r.quot;
129 		r.rem += denom;
130 	}
131 	return (r);
132 }
133