import java.io.PrintWriter;
import pal.*;

/**
 * A simple implementation of Factorial in PAL.
 *
 * @author Samuel A. Rebelsky
 * @version 1.0 of November 2002
 */
public class FactPAL
{
/*
   Base of memory: Globals
     +----------------+
     |  input         | 0
     +----------------+
     |  result        | 1
     +----------------+
        ...
    
   Frame for factorial upon entry.
     +----------------+ 
     |  Return Add.   | <- SP
     +----------------+ 
     |  Return Val.   |
     +----------------+
     |  n (parameter) |
     +----------------+
           ...
     +----------------+
     |  whatever      | <- FP
     +----------------+

   Frame for factorial after initialization
     +----------------+ 
     |  Old FP        | <- FP, SP
     +----------------+ 
     |  Return Add.   |
     +----------------+ 
     |  Return Val.   |
     +----------------+
     |  n (parameter) |
     +----------------+
 */
  public static void main(String[] args)
    throws Exception
  {
    PrintWriter out = new PrintWriter(System.out,true);
    Computer hal = new Computer(1000);
    Container input = new MemLoc(new IConstant(0));
    Container result = new MemLoc(new IConstant(1));
    Label mainLabel = new Label("MAIN");

    InstructionSequence factorial = new InstructionSequence();
    Label facBase = new Label("BASE");
    Label facRecurse = new Label("RECURSE");
    Label facCleanup = new Label("CLEANUP");

    factorial.add(new Label("FACTORIAL"));
    factorial.add(new Push(Register.fp));
    factorial.add(new Move(Register.sp, Register.fp));
    factorial.add(new Comment("If n = 0 Then");
    factorial.add(new JumpZero(new Offset(Register.fp, 3), facBase));
    factorial.add(new Jump(facRecurse));
    factorial.add(facBase);
    factorial.add(new Comment("Factorial := 1");
    factorial.add(new Jump(facCleanup));
    factorial.add(facCleanup);
    factorial.add(new Move(Register.fp, Register.sp));
    factorial.add(new Pop(Register.fp));
    factorial.add(new Jump(new MemLoc(Register.sp)));

    InstructionSequence mainBody = new InstructionSequence();

    InstructionSequence code = new InstructionSequence();
    code.add(new Label("START"));
    code.add(new Jump(mainBody));
    code.add(factorial);
    code.add(mainLabel);
    code.add(mainBody);
    code.add(new LABEL("END"));
    code.add(new Halt());

    hal.setCode(code);
    out.println("----- DUMP -----");
    hal.dump(out);
    // out.println("----- RUN ------");
    // hal.run(true);
  } // main(String[])
} // class FactPAL