Runner.java

// -*- mode: Java; c-basic-offset: 3; tab-width: 8; indent-tabs-mode: nil -*-
// Copyright (C) 2008 Andreas Krey, Ulm, Germany <a.krey@gmx.de>

package gloop;

public class Runner {

   private String [] strings;
   private byte [] code;
   private int entry;

   private static final Object nullval = new Object () {
         public String toString () { return "nullval"; }
      };

   public Runner (String [] str, byte [] a, int e) {
      strings = str;
      code = a;
      entry = e;
   }

   private static class Frame {
      public Frame stat;
      public Frame dyn;
      public int base; // Number of saved stack cells
      public Object [] data;
      public int pc;
   }

   private static class Fun {
      public Frame ctx;
      public int start;
      public int nargs;
   }

   public void run () {
      Object [] stack = new Object [100]; /// XXX Need some measure...
      int sp = 0;

      int pc = entry;
      Object acc = null;
      Frame tmp = null;
      int param = 0;
      Frame fp = new Frame ();
      fp.base = 0;
      fp.data = new Object [100];
      fp.pc = -1;
      while (true) {
         int c = code [pc ++] & 255;
         if (c >= 240) {
            param = (param << 4) | (c & 15);
            continue;
         }
         String op = Code.getCode (c);
         for (int i = 0; i < sp; i ++) {
            System.out.print (" " + stack [i]);
         }
         System.out.println (" * " + acc);
         if (param != 0) {
            System.out.println ("        [" + (pc - 1) + "] op=" + op +
                                " (" + param + ")");
         } else {
            System.out.println ("        [" + (pc - 1) + "] op=" + op);
         }
         if (op == "nop") {
         } else if (op == "up") {
            for (tmp = fp; param > 0; param --) {
               tmp = tmp.stat;
            }
         } else if (op == "lstore") {
            fp.data [param + fp.base] = acc;
            param = 0;
         } else if (op == "store") {
            tmp.data [param + tmp.base] = acc;
            param = 0;
         } else if (op == "lload") {
            acc = fp.data [param + fp.base];
            param = 0;
         } else if (op == "load") {
            acc = tmp.data [param + tmp.base];
            param = 0;
         } else if (op == "print") {
            System.out.println ("PRINT: " + acc);
         } else if (op == "strval") {
            acc = strings [param];
            param = 0;
         } else if (op == "numval") {
            acc = new Integer (param);
            param = 0;
         } else if (op == "nullval") {
            acc = nullval;
         } else if (op == "fun") {
            Fun f = new Fun ();
            f.ctx = fp;
            f.start = ((Integer)acc).intValue ();
            f.nargs = param;
            param = 0;
            acc = f;
         } else if (op == "push") {
            stack [sp ++ ] = acc;
         } else if (op == "swap") {
            Object h = acc;
            acc = stack [sp - 1];
            stack [sp - 1] = h;
         } else if (op == "mult") {
            acc = new Integer (((Integer)acc).intValue () *
                               ((Integer)stack [-- sp]).intValue ());
         } else if (op == "call") {
            Fun a = (Fun)acc;
            Frame f = new Frame ();
            if (a.nargs != param) {
               throw new IllegalArgumentException ("mismatching arg count");
            }
            f.data = new Object [100];
            f.pc = pc;
            f.base = sp - param; // We take the params from the stack!
            f.dyn = fp;
            f.stat = a.ctx;
            for (int i = 0; i < sp; i ++) {
               System.out.println ("COPY " + stack [i]);
               f.data [i] = stack [i];
            }
            pc = a.start;
            sp = 0;
            param = 0;
            fp = f;
         } else if (op == "ret") {
            pc = fp.pc;
            sp = 0;
            for (int i = 0; i < fp.base; i ++) {
               stack [sp ++] = fp.data [i];
            }
            fp = fp.dyn;
         } else if (op == "stop") {
            break;
         } else {
            throw new IllegalArgumentException ("unknown op " + op +
                                                " (" + c + ")");
         }
      }
   }
}