gonzui

    1: /*      $OpenBSD: div.c,v 1.5 2005/08/08 08:05:36 espie Exp $ */
    2: /*
    3:  * Copyright (c) 1990 Regents of the University of California.
    4:  * All rights reserved.
    5:  *
    6:  * This code is derived from software contributed to Berkeley by
    7:  * Chris Torek.
    8:  *
    9:  * Redistribution and use in source and binary forms, with or without
   10:  * modification, are permitted provided that the following conditions
   11:  * are met:
   12:  * 1. Redistributions of source code must retain the above copyright
   13:  *    notice, this list of conditions and the following disclaimer.
   14:  * 2. Redistributions in binary form must reproduce the above copyright
   15:  *    notice, this list of conditions and the following disclaimer in the
   16:  *    documentation and/or other materials provided with the distribution.
   17:  * 3. Neither the name of the University nor the names of its contributors
   18:  *    may be used to endorse or promote products derived from this software
   19:  *    without specific prior written permission.
   20:  *
   21:  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   22:  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   23:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   24:  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   25:  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   26:  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   27:  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   28:  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   29:  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   30:  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   31:  * SUCH DAMAGE.
   32:  */
   33: 
   34: #include <stdlib.h>             /* div_t */
   35: 
   36: div_t
   37: div(int num, int denom)
   38: {
   39:         div_t r;
   40: 
   41:         r.quot = num / denom;
   42:         r.rem = num % denom;
   43:         /*
   44:          * The ANSI standard says that |r.quot| <= |n/d|, where
   45:          * n/d is to be computed in infinite precision.  In other
   46:          * words, we should always truncate the quotient towards
   47:          * 0, never -infinity.
   48:          *
   49:          * Machine division and remainer may work either way when
   50:          * one or both of n or d is negative.  If only one is
   51:          * negative and r.quot has been truncated towards -inf,
   52:          * r.rem will have the same sign as denom and the opposite
   53:          * sign of num; if both are negative and r.quot has been
   54:          * truncated towards -inf, r.rem will be positive (will
   55:          * have the opposite sign of num).  These are considered
   56:          * `wrong'.
   57:          *
   58:          * If both are num and denom are positive, r will always
   59:          * be positive.
   60:          *
   61:          * This all boils down to:
   62:          *     if num >= 0, but r.rem < 0, we got the wrong answer.
   63:          * In that case, to get the right answer, add 1 to r.quot and
   64:          * subtract denom from r.rem.
   65:          */
   66:         if (num >= 0 && r.rem < 0) {
   67:                 r.quot++;
   68:                 r.rem -= denom;
   69:         }
   70:         return (r);
   71: }