factors.cpp

   1 // Push expression factors onto the stack. For example...
   2 //
   3 // Input
   4 //
   5 //       2
   6 //     3x  + 2x + 1
   7 //
   8 // Output on stack
   9 //
  10 //     [  3  ]
  11 //     [ x^2 ]
  12 //     [  2  ]
  13 //     [  x  ]
  14 //     [  1  ]
  15 //
  16 // but not necessarily in that order. Returns the number of factors.
  17
  18 #include "stdafx.h"
  19 #include "defs.h"
  20
  21 // Local U *p is OK here because no functional path to garbage collector.
  22
  23 int
  24 factors(U *p)
  25 {
  26         int h = tos;
  27         if (car(p) == symbol(ADD)) {
  28                 p = cdr(p);
  29                 while (iscons(p)) {
  30                         push_term_factors(car(p));
  31                         p = cdr(p);
  32                 }
  33         } else
  34                 push_term_factors(p);
  35         return tos - h;
  36 }
  37
  38 // Local U *p is OK here because no functional path to garbage collector.
  39
  40 void
  41 push_term_factors(U *p)
  42 {
  43         if (car(p) == symbol(MULTIPLY)) {
  44                 p = cdr(p);
  45                 while (iscons(p)) {
  46                         push(car(p));
  47                         p = cdr(p);
  48                 }
  49         } else
  50                 push(p);
  51 }