implemented PC (#11)

de/darkress/pic16f84sim/microcontroller/Stack.java

@@ -0,0 +1,51 @@
+package de.darkress.pic16f84sim.microcontroller;
+
+
+public class Stack
+{
+    private static int[] stack = new int[8];
+    private static int stackPointer = 0;
+
+    public static void push(int data)
+    {
+        stack[stackPointer] = data;
+        pointNext();
+    }
+
+    public static int pop()
+    {
+        int tmp = stack[stackPointer];
+        pointPrevious();
+        return tmp;
+    }
+
+    public static int peek()
+    {
+        return stack[(stackPointer + 7) % 8]; //Get TopOfStack -1 +8 = 7 and modulo 8 to avoid IndexOutOfBound
+    }
+
+    private static void pointNext()
+    {
+        if(stackPointer == 7)
+        {
+            stackPointer = 0;
+            return;
+        }
+        stackPointer++;
+    }
+
+    private static void pointPrevious()
+    {
+        if(stackPointer == 0)
+        {
+            stackPointer = 7;
+            return;
+        }
+        stackPointer--;
+    }
+
+    public static int getStackPointer()
+    {
+        return stackPointer;
+    }
+}