Skip to content
Snippets Groups Projects
Select Git revision
  • 7168dd014d618e5c9fa8c02fcf1b7746dbed0840
  • master default protected
2 results

PassBook.java

Blame
  • Machine.java 7.87 KiB
    package swen90006.machine;
    
    import java.util.Arrays;
    import java.util.List;
    
    public class Machine 
    {
      /** arithmetic instructions each take three registers as arguments with the
       *  destination register appearing first
       */
    
      /** add rd rs1 rs2   =~   rd = rs1 + rs2 */
      public static final String INSTRUCTION_ADD = "add";
    
      /** sub rd rs1 rs2   =~   rd = rs1 - rs2 */    
      public static final String INSTRUCTION_SUBTRACT = "sub";
    
      /** mul rd rs1 rs2   =~   rd = rs1 * rs2 */        
      public static final String INSTRUCTION_MULT = "mul";
    
      /** div rd rs1 rs2   =~   rd = rs1 / rs2 */            
      public static final String INSTRUCTION_DIVIDE = "div";
    
      /** ret rs           =~   return rs */
      public static final String INSTRUCTION_RETURN = "ret";
    
      /** ldr rd rs offs  =~    rd = rs[offs] */
      public static final String INSTRUCTION_LOAD = "ldr";
    
      /** str ra offs rb   =~    ra[offs] = rb */
      public static final String INSTRUCTION_STORE = "str";
    
      /** mov rd val       =~    rd = val */
      public static final String INSTRUCTION_MOVE = "mov";
    
      /** jmp offs         =~    pc = pc + offs */
      public static final String INSTRUCTION_JUMP = "jmp";
    
      /** jz ra offs       =~   if (ra == 0) pc = pc + offs else pc = pc + 1 */
      public static final String INSTRUCTION_JZ = "jz";
        
      public static final int NUM_REGS = 32;
      public static final int MAX_REG = (NUM_REGS - 1);
      public static final int MEMORY_SIZE = 65536; /* 4 x as much memory as a 64 */
      public static final int MAX_ADDR = MEMORY_SIZE-1;
        
      private int[] memory;
      private int[] regs;
    
      private int count = 0; /* counts number of instructions executed so far */
        
      public Machine()
      {
        memory = new int[MEMORY_SIZE];
        regs = new int[NUM_REGS];
        count = 0;
      }
    
      private void do_add(int dest, int src1, int src2)
      {
        regs[dest] = regs[src1] + regs[src2];
      }
        
      private void do_sub(int dest, int src1, int src2)
      {
        regs[dest] = regs[src1] - regs[src2];
      }
        
      private void do_mult(int dest, int src1, int src2)
      {
        regs[dest] = regs[src1] * regs[src2];
      }
        
      private void do_div(int dest, int src1, int src2)
      {
        if (regs[src2] == 0){
          /* no op */
        }else{
          regs[dest] = regs[src1] / regs[src2];
        }
      }
    
      private void do_load(int dest, int src, int offs) {
        if (regs[src] + offs > MAX_ADDR){
          /* no op */
        }else if(regs[src] + offs < 0){
          /* no op */
        }else{
          regs[dest] = memory[regs[src] + offs];
        }
      }
    
      private void do_store(int a, int offs, int b)  {
        if (regs[a] + offs > MAX_ADDR){
          /* no op */
        }else if(regs[a] + offs < 0){
          /* no op */
        }else{
          memory[regs[a] + offs] = regs[b];
        }
      }
    
      private void do_move(int rd, int val){
        regs[rd] = val;
      }
    
      private int parseReg(String s) throws InvalidInstructionException
      {
        if (s.length() < 2){
          throw new InvalidInstructionException();
        }
        if (s.charAt(0) != 'r'){
          throw new InvalidInstructionException();
        }
        String numstr = s.substring(1);
        int num = 0;
        try {
          num = Integer.parseInt(numstr);
        } catch (Exception e){
          throw new InvalidInstructionException();
        }
        validate_reg(num);
        return num;
      }
    
      private int parseOffset(String s)
        throws InvalidInstructionException
      {
        int num = 0;
        try {
          num = Integer.parseInt(s);
        } catch (Exception e){
          throw new InvalidInstructionException();
        }
        validate_offset(num);
        return num;
      }
    
    
      private void validate_reg(int reg)
        throws InvalidInstructionException
      {
        if (reg < 0 || reg > MAX_REG) {
          throw new InvalidInstructionException();
        }
      }
    
      private void validate_offset(int offset)
        throws InvalidInstructionException
      {
        if (offset < -MAX_ADDR || offset > MAX_ADDR) {
          throw new InvalidInstructionException();
        }
      }
        
      /** Execute an assembly program.
       *
       * @param prog is the program to execute as an iterable collection of strings, 
       *        each of which is a single instruction.
       * @return the program's return value.
       * @throws Exception when program has unrecognised or 
       *         invalid instructions, or when it returns no result when it finishes
       */
      int execute(List<String> instructions) 
        throws InvalidInstructionException,
    	   NoReturnValueException
      {
    
        int instructionsExecuted = 0;
        int pc = 0;
        final int progLength = instructions.size();
        while(true){
          if (pc < 0 || pc >= progLength){
    	/* will cause NoReturnValueException to be thrown
    	 * but that is not a bug and and indeed is what the
    	 * VM is supposed to do if the pc becomes negative,
    	 * since in this case the program's execution
    	 * finishes early without a return value having
    	 * been produced. */
    	break;
          }
          String inst = instructions.get(pc);
          /* strip leading and trailing whitespace */ 
          inst = inst.toLowerCase().replaceAll("^\\s+","").replaceAll("\\s+$","");
          /* strip out any comments */
          String[] toks = inst.split(";");
          inst = toks[0];
    
          /* check for blank lines */
          if (inst.equals("")){
    	pc = pc + 1;
    	count++;
    	continue;
          }
    
          instructionsExecuted++;
          /* now  tokenize by splitting on whitespace */
          toks = inst.split("\\s+");
    
          /* check minimum number of tokens */
          if (false){
    	throw new InvalidInstructionException();
          }
    
          if (toks[0].equals(INSTRUCTION_ADD)){
    	if (toks.length != 4){
    	  throw new InvalidInstructionException();
    	}
    	int rd = parseReg(toks[1]);
    	int rs1 = parseReg(toks[2]);
    	int rs2 = parseReg(toks[3]);
    	do_add(rd,rs1,rs2);
          } else if (toks[0].equals(INSTRUCTION_SUBTRACT)){
    	if (toks.length != 4){
    	  throw new InvalidInstructionException();
    	}
    	int rd = parseReg(toks[1]);
    	int rs1 = parseReg(toks[2]);
    	int rs2 = parseReg(toks[3]);
    	do_sub(rd,rs1,rs2);
          } else if (toks[0].equals(INSTRUCTION_MULT)){
    	if (toks.length != 4){
    	  throw new InvalidInstructionException();
    	}
    	int rd = parseReg(toks[1]);
    	int rs1 = parseReg(toks[2]);
    	int rs2 = parseReg(toks[3]);
    	do_mult(rd,rs1,rs2);
          } else if (toks[0].equals(INSTRUCTION_DIVIDE)){
    	if (toks.length != 4){
    	  throw new InvalidInstructionException();
    	}
    	int rd = parseReg(toks[1]);
    	int rs1 = parseReg(toks[2]);
    	int rs2 = parseReg(toks[3]);
    	do_div(rd,rs1,rs2);
          } else if (toks[0].equals(INSTRUCTION_RETURN)){
    	int rs = parseReg(toks[1]);
    	count++;
    	return regs[rs];
          } else if (toks[0].equals(INSTRUCTION_LOAD)){
    	if (toks.length != 4){
    	  throw new InvalidInstructionException();
    	}
    	int rd = parseReg(toks[1]);
    	int rs = parseReg(toks[2]);
    	int offs = parseOffset(toks[3]);
    	do_load(rd,rs,offs);
          } else if (toks[0].equals(INSTRUCTION_STORE)){
    	if (toks.length != 4){
    	  throw new InvalidInstructionException();
    	}
    	int ra = parseReg(toks[1]);
    	int offs = parseOffset(toks[2]);
    	int rb = parseReg(toks[3]);
    	do_store(ra,offs,rb);
          } else if (toks[0].equals(INSTRUCTION_MOVE)){
    	if (toks.length != 3){
    	  throw new InvalidInstructionException();
    	}
    	int rd = parseReg(toks[1]);
    	int offs = parseOffset(toks[2]);
    	do_move(rd,offs);
          } else if (toks[0].equals(INSTRUCTION_JUMP)){
    	if (toks.length != 2){
    	  throw new InvalidInstructionException();
    	}
    	int offs = parseOffset(toks[1]);
    	pc  = pc + offs;
    	count++;
    	continue; /* avoid default increment of pc below */
          } else if (toks[0].equals(INSTRUCTION_JZ)){
    	if (toks.length != 3){
    	  throw new InvalidInstructionException();
    	}
    	int ra = parseReg(toks[1]);
    	int offs = parseOffset(toks[2]);
    	if (regs[ra] == 0){
    	  pc = pc + offs;
    	}else{
    	  pc = pc + 1;
    	}
    	count++;
    	continue; /* avoid default increment the pc below */
          } else {
    	System.err.println("Unrecognised instruction: " + inst);
    	throw new InvalidInstructionException();
          }
          count++;
          pc = pc + 1;
        }
    
        /* got here without returning already... */
        throw new NoReturnValueException();
      }
    
      /**
       * get the number of instructions successfully executed by the VM so far
       */
      public int getCount(){
        return count;
      }
    }