stdlib/div.c

   1 /* Copyright (C) 1992-2013 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 /*
  19  * Copyright (c) 1990 Regents of the University of California.
  20  * All rights reserved.
  21  *
  22  * This code is derived from software contributed to Berkeley by
  23  * Chris Torek.
  24  *
  25  * Redistribution and use in source and binary forms, with or without
  26  * modification, are permitted provided that the following conditions
  27  * are met:
  28  * 1. Redistributions of source code must retain the above copyright
  29  *    notice, this list of conditions and the following disclaimer.
  30  * 2. Redistributions in binary form must reproduce the above copyright
  31  *    notice, this list of conditions and the following disclaimer in the
  32  *    documentation and/or other materials provided with the distribution.
  33  * 4. Neither the name of the University nor the names of its contributors
  34  *    may be used to endorse or promote products derived from this software
  35  *    without specific prior written permission.
  36  *
  37  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  38  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  39  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  40  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  41  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  42  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  43  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  44  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  45  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  46  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  47  * SUCH DAMAGE.
  48  */
  49
  50 #include <stdlib.h>
  51
  52 /* Return the `div_t' representation of NUMER over DENOM.  */
  53 div_t
  54 div (numer, denom)
  55      int numer, denom;
  56 {
  57   div_t result;
  58
  59   result.quot = numer / denom;
  60   result.rem = numer % denom;
  61
  62   /* The ANSI standard says that |QUOT| <= |NUMER / DENOM|, where
  63      NUMER / DENOM is to be computed in infinite precision.  In
  64      other words, we should always truncate the quotient towards
  65      zero, never -infinity.  Machine division and remainer may
  66      work either way when one or both of NUMER or DENOM is
  67      negative.  If only one is negative and QUOT has been
  68      truncated towards -infinity, REM will have the same sign as
  69      DENOM and the opposite sign of NUMER; if both are negative
  70      and QUOT has been truncated towards -infinity, REM will be
  71      positive (will have the opposite sign of NUMER).  These are
  72      considered `wrong'.  If both are NUM and DENOM are positive,
  73      RESULT will always be positive.  This all boils down to: if
  74      NUMER >= 0, but REM < 0, we got the wrong answer.  In that
  75      case, to get the right answer, add 1 to QUOT and subtract
  76      DENOM from REM.  */
  77
  78   if (numer >= 0 && result.rem < 0)
  79     {
  80       ++result.quot;
  81       result.rem -= denom;
  82     }
  83
  84   return result;
  85 }