#include "interpret.h"

extern int mem[];

extern int stack[];

extern int top;

extern int prg_size;

void interpret(struct inst * prg)
{ 
  int pc = 0, sp = 0;

  for( ; pc < prg_size ; pc++)
    {
      if(prg[pc].opcode == PUSH)
	{
	    sp = sp + 1;
	    stack[sp] = prg[pc].val;
	}
      else
	if(prg[pc].opcode == POP)
	  sp = sp - 1;
	else
	  if(prg[pc].opcode == ADD)
	    {
	      stack[sp-1] = stack[sp] + stack[sp-1];
	      sp = sp - 1;
	    }
	  else
	    if(prg[pc].opcode == SUB)
	      {
		stack[sp-1] = stack[sp-1] - stack[sp];
		sp = sp - 1;
	      }
	    else
	      if(prg[pc].opcode == MUL)
		{
		  stack[sp-1] = stack[sp] * stack[sp-1];
		  sp = sp - 1;
		}
	      else
		if(prg[pc].opcode == LD)
		    stack[sp] = mem[stack[sp]];
		else
		  if(prg[pc].opcode == ST)
		    {
		      mem[stack[sp]] = stack[sp-1];
		      sp = sp - 2;
		    }
		  else
		    {
		      printf("\n Unrecognized instruction -> %d at %d\n",
			     prg[pc].opcode, pc);
		      exit();
		    }
    }
}