qsub.cpp

   1 //      Subtract rational numbers
   2 //
   3 //      Input:          tos-2           minuend
   4 //
   5 //                      tos-1           subtrahend
   6 //
   7 //      Output:         difference on stack
   8
   9 #include "stdafx.h"
  10 #include "defs.h"
  11
  12 void
  13 qsub(void)
  14 {
  15         unsigned int *a, *ab, *b, *ba, *c;
  16
  17         save();
  18
  19         p2 = pop();
  20         p1 = pop();
  21
  22         ab = mmul(p1->u.q.a, p2->u.q.b);
  23         ba = mmul(p1->u.q.b, p2->u.q.a);
  24
  25         a = msub(ab, ba);
  26
  27         mfree(ab);
  28         mfree(ba);
  29
  30         // zero?
  31
  32         if (MZERO(a)) {
  33                 mfree(a);
  34                 push(zero);
  35                 restore();
  36                 return;
  37         }
  38
  39         b = mmul(p1->u.q.b, p2->u.q.b);
  40
  41         c = mgcd(a, b);
  42
  43         MSIGN(c) = MSIGN(b);
  44
  45         p1 = alloc();
  46
  47         p1->k = NUM;
  48
  49         p1->u.q.a = mdiv(a, c);
  50         p1->u.q.b = mdiv(b, c);
  51
  52         mfree(a);
  53         mfree(b);
  54         mfree(c);
  55
  56         push(p1);
  57
  58         restore();
  59 }