1 /* $OpenBSD: div.c,v 1.5 2005/08/08 08:05:36 espie 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 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
