xref: /illumos-gate/usr/src/lib/libc/port/gen/div.c (revision 7257d1b4)
1 /*
2  * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
3  * Use is subject to license terms.
4  */
5 
6 /*
7  * Copyright (c) 1990, 1993
8  *	The Regents of the University of California.  All rights reserved.
9  *
10  * This code is derived from software contributed to Berkeley by
11  * Chris Torek.
12  *
13  * Redistribution and use in source and binary forms, with or without
14  * modification, are permitted provided that the following conditions
15  * are met:
16  * 1. Redistributions of source code must retain the above copyright
17  *    notice, this list of conditions and the following disclaimer.
18  * 2. Redistributions in binary form must reproduce the above copyright
19  *    notice, this list of conditions and the following disclaimer in the
20  *    documentation and/or other materials provided with the distribution.
21  * 3. All advertising materials mentioning features or use of this software
22  *    must display the following acknowledgement:
23  *	This product includes software developed by the University of
24  *	California, Berkeley and its contributors.
25  * 4. Neither the name of the University nor the names of its contributors
26  *    may be used to endorse or promote products derived from this software
27  *    without specific prior written permission.
28  *
29  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
30  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
31  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
32  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
33  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
34  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
35  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
36  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
37  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
38  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
39  * SUCH DAMAGE.
40  */
41 
42 #pragma ident	"%Z%%M%	%I%	%E% SMI"
43 
44 #include "lint.h"
45 #include <sys/types.h>
46 #include <stdlib.h>
47 
48 div_t
div(num,denom)49 div(num, denom)
50 	int num, denom;
51 {
52 	div_t r;
53 
54 	r.quot = num / denom;
55 	r.rem = num % denom;
56 	/*
57 	 * The ANSI standard says that |r.quot| <= |n/d|, where
58 	 * n/d is to be computed in infinite precision.  In other
59 	 * words, we should always truncate the quotient towards
60 	 * 0, never -infinity.
61 	 *
62 	 * Machine division and remainer may work either way when
63 	 * one or both of n or d is negative.  If only one is
64 	 * negative and r.quot has been truncated towards -inf,
65 	 * r.rem will have the same sign as denom and the opposite
66 	 * sign of num; if both are negative and r.quot has been
67 	 * truncated towards -inf, r.rem will be positive (will
68 	 * have the opposite sign of num).  These are considered
69 	 * `wrong'.
70 	 *
71 	 * If both are num and denom are positive, r will always
72 	 * be positive.
73 	 *
74 	 * This all boils down to:
75 	 *	if num >= 0, but r.rem < 0, we got the wrong answer.
76 	 * In that case, to get the right answer, add 1 to r.quot and
77 	 * subtract denom from r.rem.
78 	 */
79 	if (num >= 0 && r.rem < 0) {
80 		r.quot++;
81 		r.rem -= denom;
82 	}
83 	return (r);
84 }
85 
86 ldiv_t
ldiv(num,denom)87 ldiv(num, denom)
88 	long num, denom;
89 {
90 	ldiv_t r;
91 
92 	/* see div() for comments */
93 
94 	r.quot = num / denom;
95 	r.rem = num % denom;
96 	if (num >= 0 && r.rem < 0) {
97 		r.quot++;
98 		r.rem -= denom;
99 	}
100 	return (r);
101 }
102