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  1. /*
  2. FUNCTION
  3. <<div>>---divide two integers
  4.  
  5. INDEX
  6.         div
  7.  
  8. ANSI_SYNOPSIS
  9.         #include <stdlib.h>
  10.         div_t div(int <[n]>, int <[d]>);
  11.  
  12. TRAD_SYNOPSIS
  13.         #include <stdlib.h>
  14.         div_t div(<[n]>, <[d]>)
  15.         int <[n]>, <[d]>;
  16.  
  17. DESCRIPTION
  18. Divide
  19. @tex
  20. $n/d$,
  21. @end tex
  22. @ifnottex
  23. <[n]>/<[d]>,
  24. @end ifnottex
  25. returning quotient and remainder as two integers in a structure <<div_t>>.
  26.  
  27. RETURNS
  28. The result is represented with the structure
  29.  
  30. . typedef struct
  31. . {
  32. .  int quot;
  33. .  int rem;
  34. . } div_t;
  35.  
  36. where the <<quot>> field represents the quotient, and <<rem>> the
  37. remainder.  For nonzero <[d]>, if `<<<[r]> = div(<[n]>,<[d]>);>>' then
  38. <[n]> equals `<<<[r]>.rem + <[d]>*<[r]>.quot>>'.
  39.  
  40. To divide <<long>> rather than <<int>> values, use the similar
  41. function <<ldiv>>.
  42.  
  43. PORTABILITY
  44. <<div>> is ANSI.
  45.  
  46. No supporting OS subroutines are required.
  47. */
  48.  
  49. /*
  50.  * Copyright (c) 1990 Regents of the University of California.
  51.  * All rights reserved.
  52.  *
  53.  * This code is derived from software contributed to Berkeley by
  54.  * Chris Torek.
  55.  *
  56.  * Redistribution and use in source and binary forms, with or without
  57.  * modification, are permitted provided that the following conditions
  58.  * are met:
  59.  * 1. Redistributions of source code must retain the above copyright
  60.  *    notice, this list of conditions and the following disclaimer.
  61.  * 2. Redistributions in binary form must reproduce the above copyright
  62.  *    notice, this list of conditions and the following disclaimer in the
  63.  *    documentation and/or other materials provided with the distribution.
  64.  * 3. All advertising materials mentioning features or use of this software
  65.  *    must display the following acknowledgement:
  66.  *      This product includes software developed by the University of
  67.  *      California, Berkeley and its contributors.
  68.  * 4. Neither the name of the University nor the names of its contributors
  69.  *    may be used to endorse or promote products derived from this software
  70.  *    without specific prior written permission.
  71.  *
  72.  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  73.  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  74.  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  75.  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  76.  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  77.  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  78.  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  79.  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  80.  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  81.  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  82.  * SUCH DAMAGE.
  83.  */
  84.  
  85. #include <_ansi.h>
  86. #include <stdlib.h>             /* div_t */
  87.  
  88. div_t
  89. _DEFUN (div, (num, denom),
  90.         int num _AND
  91.         int denom)
  92. {
  93.         div_t r;
  94.  
  95.         r.quot = num / denom;
  96.         r.rem = num % denom;
  97.         /*
  98.          * The ANSI standard says that |r.quot| <= |n/d|, where
  99.          * n/d is to be computed in infinite precision.  In other
  100.          * words, we should always truncate the quotient towards
  101.          * 0, never -infinity or +infinity.
  102.          *
  103.          * Machine division and remainer may work either way when
  104.          * one or both of n or d is negative.  If only one is
  105.          * negative and r.quot has been truncated towards -inf,
  106.          * r.rem will have the same sign as denom and the opposite
  107.          * sign of num; if both are negative and r.quot has been
  108.          * truncated towards -inf, r.rem will be positive (will
  109.          * have the opposite sign of num).  These are considered
  110.          * `wrong'.
  111.          *
  112.          * If both are num and denom are positive, r will always
  113.          * be positive.
  114.          *
  115.          * This all boils down to:
  116.          *      if num >= 0, but r.rem < 0, we got the wrong answer.
  117.          * In that case, to get the right answer, add 1 to r.quot and
  118.          * subtract denom from r.rem.
  119.          *      if num < 0, but r.rem > 0, we also have the wrong answer.
  120.          * In this case, to get the right answer, subtract 1 from r.quot and
  121.          * add denom to r.rem.
  122.          */
  123.         if (num >= 0 && r.rem < 0) {
  124.                 ++r.quot;
  125.                 r.rem -= denom;
  126.         }
  127.         else if (num < 0 && r.rem > 0) {
  128.                 --r.quot;
  129.                 r.rem += denom;
  130.         }
  131.         return (r);
  132. }
  133.