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;
}
}