1 /* $NetBSD: div.c,v 1.8 2012/06/25 22:32:45 abs Exp $ */ 2 3 /* 4 * Copyright (c) 1990, 1993 5 * The Regents of the University of California. 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. Neither the name of the University nor the names of its contributors 19 * may be used to endorse or promote products derived from this software 20 * without specific prior written permission. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 */ 34 35 #include <sys/cdefs.h> 36 #if defined(LIBC_SCCS) && !defined(lint) 37 #if 0 38 static char sccsid[] = "@(#)div.c 8.1 (Berkeley) 6/4/93"; 39 #else 40 __RCSID("$NetBSD: div.c,v 1.8 2012/06/25 22:32:45 abs Exp $"); 41 #endif 42 #endif /* LIBC_SCCS and not lint */ 43 44 #include <stdlib.h> /* div_t */ 45 46 div_t 47 div(int num, int denom) 48 { 49 div_t r; 50 51 r.quot = num / denom; 52 r.rem = num % denom; 53 /* 54 * The ANSI standard says that |r.quot| <= |n/d|, where 55 * n/d is to be computed in infinite precision. In other 56 * words, we should always truncate the quotient towards 57 * 0, never -infinity. 58 * 59 * Machine division and remainer may work either way when 60 * one or both of n or d is negative. If only one is 61 * negative and r.quot has been truncated towards -inf, 62 * r.rem will have the same sign as denom and the opposite 63 * sign of num; if both are negative and r.quot has been 64 * truncated towards -inf, r.rem will be positive (will 65 * have the opposite sign of num). These are considered 66 * `wrong'. 67 * 68 * If both are num and denom are positive, r will always 69 * be positive. 70 * 71 * This all boils down to: 72 * if num >= 0, but r.rem < 0, we got the wrong answer. 73 * In that case, to get the right answer, add 1 to r.quot and 74 * subtract denom from r.rem. 75 */ 76 if (num >= 0 && r.rem < 0) { 77 r.quot++; 78 r.rem -= denom; 79 } 80 return (r); 81 } 82
