condense.cpp

   1 // Condense an expression by factoring common terms.
   2
   3 #include "stdafx.h"
   4 #include "defs.h"
   5
   6 void
   7 eval_condense(void)
   8 {
   9         push(cadr(p1));
  10         eval();
  11         Condense();
  12 }
  13
  14 void
  15 Condense(void)
  16 {
  17         int tmp;
  18         tmp = expanding;
  19         save();
  20         yycondense();
  21         restore();
  22         expanding = tmp;
  23 }
  24
  25 void
  26 yycondense(void)
  27 {
  28         expanding = 0;
  29
  30         p1 = pop();
  31
  32         if (car(p1) != symbol(ADD)) {
  33                 push(p1);
  34                 return;
  35         }
  36
  37         // get gcd of all terms
  38
  39         p3 = cdr(p1);
  40         push(car(p3));
  41         p3 = cdr(p3);
  42         while (iscons(p3)) {
  43                 push(car(p3));
  44                 gcd();
  45                 p3 = cdr(p3);
  46         }
  47
  48         // divide each term by gcd
  49
  50         inverse();
  51         p2 = pop();
  52         push(zero);
  53         p3 = cdr(p1);
  54         while (iscons(p3)) {
  55                 push(p2);
  56                 push(car(p3));
  57                 multiply();
  58                 add();
  59                 p3 = cdr(p3);
  60         }
  61
  62         // We multiplied above w/o expanding so sum factors cancelled.
  63
  64         // Now we expand which which normalizes the result and, in some cases,
  65         // simplifies it too (see test case H).
  66
  67         yyexpand();
  68
  69         // multiply result by gcd
  70
  71         push(p2);
  72         divide();
  73 }