Add PUSHF and POPF instructions

Server/src/main/java/net/simon987/server/assembly/CPU.java

@@ -97,6 +97,8 @@ public class CPU implements JSONSerialisable {
         instructionSet.add(new JncInstruction(this));
         instructionSet.add(new JnoInstruction(this));
         instructionSet.add(new JoInstruction(this));
+        instructionSet.add(new PushfInstruction(this));
+        instructionSet.add(new PopfInstruction(this));
 
         status = new Status();
         memory = new Memory(config.getInt("memory_size"));

Server/src/main/java/net/simon987/server/assembly/Status.java

@@ -132,4 +132,20 @@ public class Status {
     public void setErrorFlag(boolean errorFlag) {
         this.errorFlag = errorFlag;
     }
+
+    public char toByte() {
+        char stat = 0; 
+        stat = (char) (stat | ((signFlag ? 1 : 0) << 3));
+        stat = (char) (stat | ((zeroFlag ? 1 : 0) << 2));
+        stat = (char) (stat | ((carryFlag ? 1 : 0) << 1));
+        stat = (char) (stat | (overflowFlag ? 1 : 0));
+        return stat;
+    }
+    
+    public void fromByte(char stat) {
+        setSignFlag((stat & (1 << 3)) != 0);
+        setZeroFlag((stat & (1 << 2)) != 0);
+        setCarryFlag((stat & (1 << 1)) != 0);
+        setOverflowFlag((stat & 1) != 0);    	
+    }
 }

Server/src/main/java/net/simon987/server/assembly/instruction/PopfInstruction.java

@@ -0,0 +1,46 @@
+package net.simon987.server.assembly.instruction;
+
+import net.simon987.server.assembly.CPU;
+import net.simon987.server.assembly.Instruction;
+import net.simon987.server.assembly.Register;
+import net.simon987.server.assembly.Status;
+
+/**
+ * Pops a single word off the top of the stack and sets the CPU flags to it.
+ */
+public class PopfInstruction extends Instruction {
+
+    /**
+     * Opcode of the instruction
+     */
+    public static final int OPCODE = 44;
+
+    private CPU cpu;
+
+    public PopfInstruction(CPU cpu) {
+        super("popf", OPCODE);
+
+        this.cpu = cpu;
+    }
+
+    @Override
+    public Status execute(Status status) {
+
+        Register sp = cpu.getRegisterSet().getRegister("SP");
+
+        // Get the word on the top of the stack
+        char flags = (char) cpu.getMemory().get(sp.getValue());
+
+        // Overwrite the CPU flags
+        status.fromByte(flags);
+
+        // Increment SP
+        sp.setValue(sp.getValue() + 1);
+        
+        return status;
+    }
+
+    public boolean noOperandsValid() {
+        return true;
+    }
+}

Server/src/main/java/net/simon987/server/assembly/instruction/PushfInstruction.java

@@ -0,0 +1,42 @@
+package net.simon987.server.assembly.instruction;
+
+import net.simon987.server.assembly.CPU;
+import net.simon987.server.assembly.Instruction;
+import net.simon987.server.assembly.Register;
+import net.simon987.server.assembly.Status;
+
+/**
+ * Pushes the current CPU flags onto the stack.
+ */
+public class PushfInstruction extends Instruction {
+
+    /**
+     * Opcode of the instruction
+     */
+    public static final int OPCODE = 43;
+
+    private CPU cpu;
+
+    public PushfInstruction(CPU cpu) {
+        super("pushf", OPCODE);
+
+        this.cpu = cpu;
+    }
+
+    @Override
+    public Status execute(Status status) {
+
+        // Decrement SP
+        Register sp = cpu.getRegisterSet().getRegister("SP");
+        sp.setValue(sp.getValue() - 1);
+
+        // Push the current flags
+        cpu.getMemory().set(sp.getValue(), status.toByte());
+
+        return status;
+    }
+
+    public boolean noOperandsValid() {
+        return true;
+    }
+}