lib/libc/stdlib/div.c

   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 }