lib/libc/stdlib/div.c

   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  * 4. Neither the name of the University nor the names of its contributors
  17  *    may be used to endorse or promote products derived from this software
  18  *    without specific prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  *
  32  * @(#)div.c    8.1 (Berkeley) 6/4/93
  33  * $FreeBSD: src/lib/libc/stdlib/div.c,v 1.3 2007/01/09 00:28:09 imp Exp $
  34  * $DragonFly: src/lib/libc/stdlib/div.c,v 1.3 2005/11/20 12:37:48 swildner Exp $
  35  */
  36
  37 #include <stdlib.h>             /* div_t */
  38
  39 div_t
  40 div(int num, int denom)
  41 {
  42         div_t r;
  43
  44         r.quot = num / denom;
  45         r.rem = num % denom;
  46         /*
  47          * The ANSI standard says that |r.quot| <= |n/d|, where
  48          * n/d is to be computed in infinite precision.  In other
  49          * words, we should always truncate the quotient towards
  50          * 0, never -infinity.
  51          *
  52          * Machine division and remainer may work either way when
  53          * one or both of n or d is negative.  If only one is
  54          * negative and r.quot has been truncated towards -inf,
  55          * r.rem will have the same sign as denom and the opposite
  56          * sign of num; if both are negative and r.quot has been
  57          * truncated towards -inf, r.rem will be positive (will
  58          * have the opposite sign of num).  These are considered
  59          * `wrong'.
  60          *
  61          * If both are num and denom are positive, r will always
  62          * be positive.
  63          *
  64          * This all boils down to:
  65          *      if num >= 0, but r.rem < 0, we got the wrong answer.
  66          * In that case, to get the right answer, add 1 to r.quot and
  67          * subtract denom from r.rem.
  68          */
  69         if (num >= 0 && r.rem < 0) {
  70                 r.quot++;
  71                 r.rem -= denom;
  72         }
  73         return (r);
  74 }