120 lines
1.8 KiB
C++
120 lines
1.8 KiB
C++
// _______
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// | | <- stack
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// | |
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// |_______|
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// | | <- stack + tos
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// | |
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// | |
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// |_______|
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// | | <- frame
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// |_______|
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// <- stack + TOS
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//
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// The stack grows from low memory towards high memory. This is so that
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// multiple expressions can be pushed on the stack and then accessed as an
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// array.
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//
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// The frame area holds local variables and grows from high memory towards
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// low memory. The frame area makes local variables visible to the garbage
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// collector.
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#include "stdafx.h"
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#include "defs.h"
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U **frame, **stack;
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int tos;
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void
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push(U *p)
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{
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if (stack + tos >= frame)
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stop("stack overflow");
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stack[tos++] = p;
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}
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U *
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pop()
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{
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if (tos == 0)
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stop("stack underflow");
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return stack[--tos];
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}
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void
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push_frame(int n)
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{
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int i;
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frame -= n;
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if (frame < stack + tos)
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stop("frame overflow, circular reference?");
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for (i = 0; i < n; i++)
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frame[i] = symbol(NIL);
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}
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void
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pop_frame(int n)
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{
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frame += n;
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if (frame > stack + TOS)
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stop("frame underflow");
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}
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void
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save(void)
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{
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frame -= 10;
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if (frame < stack + tos)
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stop("frame overflow, circular reference?");
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frame[0] = p0;
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frame[1] = p1;
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frame[2] = p2;
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frame[3] = p3;
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frame[4] = p4;
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frame[5] = p5;
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frame[6] = p6;
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frame[7] = p7;
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frame[8] = p8;
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frame[9] = p9;
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}
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void
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restore(void)
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{
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if (frame > stack + TOS - 10)
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stop("frame underflow");
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p0 = frame[0];
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p1 = frame[1];
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p2 = frame[2];
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p3 = frame[3];
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p4 = frame[4];
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p5 = frame[5];
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p6 = frame[6];
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p7 = frame[7];
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p8 = frame[8];
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p9 = frame[9];
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frame += 10;
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}
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// Local U * is OK here because there is no functional path to the garbage collector.
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void
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swap(void)
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{
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U *p, *q;
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p = pop();
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q = pop();
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push(p);
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push(q);
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}
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// Local U * is OK here because there is no functional path to the garbage collector.
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void
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dupl(void)
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{
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U *p;
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p = pop();
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push(p);
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push(p);
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}
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