distill.cpp

   1 #include "stdafx.h"
   2
   3 #include "defs.h"
   4
   5 static void _distill(void);
   6
   7 //      take expr and push all constant subexpr
   8
   9 //      p1      expr
  10
  11 //      p2      independent variable (like x)
  12
  13 void
  14 distill(void)
  15 {
  16         save();
  17         _distill();
  18         restore();
  19 }
  20
  21 static void
  22 _distill(void)
  23 {
  24         p2 = pop();
  25         p1 = pop();
  26
  27         // is the entire expression constant?
  28
  29         if (find(p1, p2) == 0) {
  30                 push(p1);
  31                 //push(p1);     // may need later for pushing both +a, -a
  32                 //negate();
  33                 return;
  34         }
  35
  36         // sum?
  37
  38         if (isadd(p1)) {
  39                 distill_sum();
  40                 return;
  41         }
  42
  43         // product?
  44
  45         if (car(p1) == symbol(MULTIPLY)) {
  46                 distill_product();
  47                 return;
  48         }
  49
  50         // naive distill if not sum or product
  51
  52         p3 = cdr(p1);
  53         while (iscons(p3)) {
  54                 push(car(p3));
  55                 push(p2);
  56                 distill();
  57                 p3 = cdr(p3);
  58         }
  59 }
  60
  61 void
  62 distill_sum(void)
  63 {
  64         int h;
  65
  66         // distill terms involving x
  67
  68         p3 = cdr(p1);
  69
  70         while (iscons(p3)) {
  71                 if (find(car(p3), p2)) {
  72                         push(car(p3));
  73                         push(p2);
  74                         distill();
  75                 }
  76                 p3 = cdr(p3);
  77         }
  78
  79         // add together all constant terms
  80
  81         h = tos;
  82
  83         p3 = cdr(p1);
  84
  85         while (iscons(p3)) {
  86                 if (find(car(p3), p2) == 0)
  87                         push(car(p3));
  88                 p3 = cdr(p3);
  89         }
  90
  91         if (tos - h) {
  92                 add_all(tos - h);
  93                 p3 = pop();
  94                 push(p3);
  95                 push(p3);
  96                 negate();       // need both +a, -a for some integrals
  97         }
  98 }
  99
 100 void
 101 distill_product(void)
 102 {
 103         int h;
 104
 105         // distill factors involving x
 106
 107         p3 = cdr(p1);
 108
 109         while (iscons(p3)) {
 110                 if (find(car(p3), p2)) {
 111                         push(car(p3));
 112                         push(p2);
 113                         distill();
 114                 }
 115                 p3 = cdr(p3);
 116         }
 117
 118         // multiply together all constant factors
 119
 120         h = tos;
 121
 122         p3 = cdr(p1);
 123
 124         while (iscons(p3)) {
 125                 if (find(car(p3), p2) == 0)
 126                         push(car(p3));
 127                 p3 = cdr(p3);
 128         }
 129
 130         if (tos - h) {
 131                 multiply_all(tos - h);
 132                 //p3 = pop();   // may need later for pushing both +a, -a
 133                 //push(p3);
 134                 //push(p3);
 135                 //negate();
 136         }
 137 }