stdlib/div.c

   1 /* Copyright (C) 1992 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 Library General Public License as
   6 published by the Free Software Foundation; either version 2 of the
   7 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 Library General Public License for more details.
  13
  14 You should have received a copy of the GNU Library General Public
  15 License along with the GNU C Library; see the file COPYING.LIB.  If
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 /*
  20  * Copyright (c) 1990 Regents of the University of California.
  21  * All rights reserved.
  22  *
  23  * This code is derived from software contributed to Berkeley by
  24  * Chris Torek.
  25  *
  26  * Redistribution and use in source and binary forms, with or without
  27  * modification, are permitted provided that the following conditions
  28  * are met:
  29  * 1. Redistributions of source code must retain the above copyright
  30  *    notice, this list of conditions and the following disclaimer.
  31  * 2. Redistributions in binary form must reproduce the above copyright
  32  *    notice, this list of conditions and the following disclaimer in the
  33  *    documentation and/or other materials provided with the distribution.
  34  * 3. All advertising materials mentioning features or use of this software
  35  *    must display the following acknowledgement:
  36  *      This product includes software developed by the University of
  37  *      California, Berkeley and its contributors.
  38  * 4. Neither the name of the University nor the names of its contributors
  39  *    may be used to endorse or promote products derived from this software
  40  *    without specific prior written permission.
  41  *
  42  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  43  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  44  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  45  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  46  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  47  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  48  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  49  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  50  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  51  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  52  * SUCH DAMAGE.
  53  */
  54
  55 #include <ansidecl.h>
  56 #include <stdlib.h>
  57
  58
  59 /* Return the `div_t' representation of NUMER over DENOM.  */
  60 __CONSTVALUE
  61 div_t
  62 DEFUN(div, (numer, denom), int numer AND int denom)
  63 {
  64   div_t result;
  65
  66   result.quot = numer / denom;
  67   result.rem = numer % denom;
  68
  69   /* The ANSI standard says that |QUOT| <= |NUMER / DENOM|, where
  70      NUMER / DENOM is to be computed in infinite precision.  In
  71      other words, we should always truncate the quotient towards
  72      zero, never -infinity.  Machine division and remainer may
  73      work either way when one or both of NUMER or DENOM is
  74      negative.  If only one is negative and QUOT has been
  75      truncated towards -infinity, REM will have the same sign as
  76      DENOM and the opposite sign of NUMER; if both are negative
  77      and QUOT has been truncated towards -infinity, REM will be
  78      positive (will have the opposite sign of NUMER).  These are
  79      considered `wrong'.  If both are NUM and DENOM are positive,
  80      RESULT will always be positive.  This all boils down to: if
  81      NUMER >= 0, but REM < 0, we got the wrong answer.  In that
  82      case, to get the right answer, add 1 to QUOT and subtract
  83      DENOM from REM.  */
  84
  85   if (numer >= 0 && result.rem < 0)
  86     {
  87       ++result.quot;
  88       result.rem -= denom;
  89     }
  90
  91   return result;
  92 }