stack.cpp

   1 //       _______
   2 //      |       | <- stack
   3 //      |       |
   4 //      |_______|
   5 //      |       | <- stack + tos
   6 //      |       |
   7 //      |       |
   8 //      |_______|
   9 //      |       | <- frame
  10 //      |_______|
  11 //                <- stack + TOS
  12 //
  13 //      The stack grows from low memory towards high memory. This is so that
  14 //      multiple expressions can be pushed on the stack and then accessed as an
  15 //      array.
  16 //
  17 //      The frame area holds local variables and grows from high memory towards
  18 //      low memory. The frame area makes local variables visible to the garbage
  19 //      collector.
  20
  21 #include "stdafx.h"
  22 #include "defs.h"
  23
  24 U **frame, **stack;
  25 int tos;
  26
  27 void
  28 push(U *p)
  29 {
  30         if (stack + tos >= frame)
  31                 stop("stack overflow");
  32         stack[tos++] = p;
  33 }
  34
  35 U *
  36 pop()
  37 {
  38         if (tos == 0)
  39                 stop("stack underflow");
  40         return stack[--tos];
  41 }
  42
  43 void
  44 push_frame(int n)
  45 {
  46         int i;
  47         frame -= n;
  48         if (frame < stack + tos)
  49                 stop("frame overflow, circular reference?");
  50         for (i = 0; i < n; i++)
  51                 frame[i] = symbol(NIL);
  52 }
  53
  54 void
  55 pop_frame(int n)
  56 {
  57         frame += n;
  58         if (frame > stack + TOS)
  59                 stop("frame underflow");
  60 }
  61
  62 void
  63 save(void)
  64 {
  65         frame -= 10;
  66         if (frame < stack + tos)
  67                 stop("frame overflow, circular reference?");
  68         frame[0] = p0;
  69         frame[1] = p1;
  70         frame[2] = p2;
  71         frame[3] = p3;
  72         frame[4] = p4;
  73         frame[5] = p5;
  74         frame[6] = p6;
  75         frame[7] = p7;
  76         frame[8] = p8;
  77         frame[9] = p9;
  78 }
  79
  80 void
  81 restore(void)
  82 {
  83         if (frame > stack + TOS - 10)
  84                 stop("frame underflow");
  85         p0 = frame[0];
  86         p1 = frame[1];
  87         p2 = frame[2];
  88         p3 = frame[3];
  89         p4 = frame[4];
  90         p5 = frame[5];
  91         p6 = frame[6];
  92         p7 = frame[7];
  93         p8 = frame[8];
  94         p9 = frame[9];
  95         frame += 10;
  96 }
  97
  98 // Local U * is OK here because there is no functional path to the garbage collector.
  99
 100 void
 101 swap(void)
 102 {
 103         U *p, *q;
 104         p = pop();
 105         q = pop();
 106         push(p);
 107         push(q);
 108 }
 109
 110 // Local U * is OK here because there is no functional path to the garbage collector.
 111
 112 void
 113 dupl(void)
 114 {
 115         U *p;
 116         p = pop();
 117         push(p);
 118         push(p);
 119 }