1 /* $NetBSD: div.c,v 1.6 1998/01/30 23:37:52 perry 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. 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 #include <sys/cdefs.h> 40 #if defined(LIBC_SCCS) && !defined(lint) 41 #if 0 42 static char sccsid[] = "@(#)div.c 8.1 (Berkeley) 6/4/93"; 43 #else 44 __RCSID("$NetBSD: div.c,v 1.6 1998/01/30 23:37:52 perry Exp $"); 45 #endif 46 #endif /* LIBC_SCCS and not lint */ 47 48 #include <stdlib.h> /* div_t */ 49 50 div_t 51 div(num, denom) 52 int num, denom; 53 { 54 div_t r; 55 56 r.quot = num / denom; 57 r.rem = num % denom; 58 /* 59 * The ANSI standard says that |r.quot| <= |n/d|, where 60 * n/d is to be computed in infinite precision. In other 61 * words, we should always truncate the quotient towards 62 * 0, never -infinity. 63 * 64 * Machine division and remainer may work either way when 65 * one or both of n or d is negative. If only one is 66 * negative and r.quot has been truncated towards -inf, 67 * r.rem will have the same sign as denom and the opposite 68 * sign of num; if both are negative and r.quot has been 69 * truncated towards -inf, r.rem will be positive (will 70 * have the opposite sign of num). These are considered 71 * `wrong'. 72 * 73 * If both are num and denom are positive, r will always 74 * be positive. 75 * 76 * This all boils down to: 77 * if num >= 0, but r.rem < 0, we got the wrong answer. 78 * In that case, to get the right answer, add 1 to r.quot and 79 * subtract denom from r.rem. 80 */ 81 if (num >= 0 && r.rem < 0) { 82 r.quot++; 83 r.rem -= denom; 84 } 85 return (r); 86 } 87