1 /* 2 * Copyright (c) 1990, 1993 3 * The Regents of the University of California. All rights reserved. 4 * 5 * This code is derived from software contributed to Berkeley by 6 * Chris Torek. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 3. All advertising materials mentioning features or use of this software 17 * must display the following acknowledgement: 18 * This product includes software developed by the University of 19 * California, Berkeley and its contributors. 20 * 4. Neither the name of the University nor the names of its contributors 21 * may be used to endorse or promote products derived from this software 22 * without specific prior written permission. 23 * 24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34 * SUCH DAMAGE. 35 * 36 * @(#)div.c 8.1 (Berkeley) 6/4/93 37 * $DragonFly: src/lib/libc/stdlib/div.c,v 1.2 2003/06/17 04:26:46 dillon Exp $ 38 */ 39 40 #include <stdlib.h> /* div_t */ 41 42 div_t 43 div(num, denom) 44 int num, denom; 45 { 46 div_t r; 47 48 r.quot = num / denom; 49 r.rem = num % denom; 50 /* 51 * The ANSI standard says that |r.quot| <= |n/d|, where 52 * n/d is to be computed in infinite precision. In other 53 * words, we should always truncate the quotient towards 54 * 0, never -infinity. 55 * 56 * Machine division and remainer may work either way when 57 * one or both of n or d is negative. If only one is 58 * negative and r.quot has been truncated towards -inf, 59 * r.rem will have the same sign as denom and the opposite 60 * sign of num; if both are negative and r.quot has been 61 * truncated towards -inf, r.rem will be positive (will 62 * have the opposite sign of num). These are considered 63 * `wrong'. 64 * 65 * If both are num and denom are positive, r will always 66 * be positive. 67 * 68 * This all boils down to: 69 * if num >= 0, but r.rem < 0, we got the wrong answer. 70 * In that case, to get the right answer, add 1 to r.quot and 71 * subtract denom from r.rem. 72 */ 73 if (num >= 0 && r.rem < 0) { 74 r.quot++; 75 r.rem -= denom; 76 } 77 return (r); 78 } 79