1 /* $NetBSD: div.c,v 1.4 1995/12/28 08:52:13 thorpej Exp $ */ 2 3 /* 4 * Copyright (c) 1990 Regents of the University of California. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to Berkeley by 8 * Chris Torek. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the University of 21 * California, Berkeley and its contributors. 22 * 4. Neither the name of the University nor the names of its contributors 23 * may be used to endorse or promote products derived from this software 24 * without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36 * SUCH DAMAGE. 37 */ 38 39 #if defined(LIBC_SCCS) && !defined(lint) 40 #if 0 41 static char *sccsid = "from: @(#)div.c 5.2 (Berkeley) 4/16/91"; 42 #else 43 static char *rcsid = "$NetBSD: div.c,v 1.4 1995/12/28 08:52:13 thorpej Exp $"; 44 #endif 45 #endif /* LIBC_SCCS and not lint */ 46 47 #include <stdlib.h> /* div_t */ 48 49 div_t 50 div(num, denom) 51 int num, denom; 52 { 53 div_t r; 54 55 r.quot = num / denom; 56 r.rem = num % denom; 57 /* 58 * The ANSI standard says that |r.quot| <= |n/d|, where 59 * n/d is to be computed in infinite precision. In other 60 * words, we should always truncate the quotient towards 61 * 0, never -infinity. 62 * 63 * Machine division and remainer may work either way when 64 * one or both of n or d is negative. If only one is 65 * negative and r.quot has been truncated towards -inf, 66 * r.rem will have the same sign as denom and the opposite 67 * sign of num; if both are negative and r.quot has been 68 * truncated towards -inf, r.rem will be positive (will 69 * have the opposite sign of num). These are considered 70 * `wrong'. 71 * 72 * If both are num and denom are positive, r will always 73 * be positive. 74 * 75 * This all boils down to: 76 * if num >= 0, but r.rem < 0, we got the wrong answer. 77 * In that case, to get the right answer, add 1 to r.quot and 78 * subtract denom from r.rem. 79 */ 80 if (num >= 0 && r.rem < 0) { 81 r.quot++; 82 r.rem -= denom; 83 } 84 return (r); 85 } 86