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mutants/mutant-4/swen90006/machine/Machine.java

+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 (toks.length < 2){
+	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;
+  }
+}