Functional Sublw instruction (#8)

* Functional Sublw instruction

* Fixed zeroBit in Addlw after overflow and result == 0

commands/Sublw.java

@@ -0,0 +1,45 @@
+package commands;
+
+import registers.Memory;
+
+public class Sublw extends CommandUtils implements Command
+{
+    private final int literal;
+
+    public Sublw(int input)
+    {
+        literal = input & 0x00FF;
+    }
+
+    @Override
+    protected void checkCarryBit(int result)
+    {
+        if(result <= 255){
+            Memory.clearCarryBit();
+        } else{
+            Memory.setCarryBit();
+        }
+    }
+
+    @Override
+    protected void checkDigitCarryBit(int literal)
+    {
+        if(((literal & 0x0F) - (Memory.workingRegister & 0x0F)) < 0){
+            Memory.clearDigitCarryBit();
+        } else{
+            Memory.setDigitCarryBit();
+        }
+    }
+
+    @Override
+    public void execute()
+    {
+        int result = literal - Memory.workingRegister + 256;
+
+        checkZeroBit(result);
+        checkCarryBit(result);
+        checkDigitCarryBit(literal);
+
+        Memory.workingRegister = result % 256;
+    }
+}