From deb3859dffce1c82b858b31787adecabc29954df Mon Sep 17 00:00:00 2001
From: Ethan Lafrenais <elafrenais12@gmail.com>
Date: Sun, 31 Dec 2017 18:25:46 -0500
Subject: [PATCH] Add PUSHF and POPF instructions

---
 .../net/simon987/server/assembly/CPU.java     |  2 +
 .../net/simon987/server/assembly/Status.java  | 16 +++++++
 .../assembly/instruction/PopfInstruction.java | 46 +++++++++++++++++++
 .../instruction/PushfInstruction.java         | 42 +++++++++++++++++
 4 files changed, 106 insertions(+)
 create mode 100644 Server/src/main/java/net/simon987/server/assembly/instruction/PopfInstruction.java
 create mode 100644 Server/src/main/java/net/simon987/server/assembly/instruction/PushfInstruction.java

diff --git a/Server/src/main/java/net/simon987/server/assembly/CPU.java b/Server/src/main/java/net/simon987/server/assembly/CPU.java
index 50b49e4..a2e9966 100755
--- a/Server/src/main/java/net/simon987/server/assembly/CPU.java
+++ b/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"));
diff --git a/Server/src/main/java/net/simon987/server/assembly/Status.java b/Server/src/main/java/net/simon987/server/assembly/Status.java
index 4b370a6..f812e80 100755
--- a/Server/src/main/java/net/simon987/server/assembly/Status.java
+++ b/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);    	
+    }
 }
diff --git a/Server/src/main/java/net/simon987/server/assembly/instruction/PopfInstruction.java b/Server/src/main/java/net/simon987/server/assembly/instruction/PopfInstruction.java
new file mode 100644
index 0000000..2ec374b
--- /dev/null
+++ b/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;
+    }
+}
\ No newline at end of file
diff --git a/Server/src/main/java/net/simon987/server/assembly/instruction/PushfInstruction.java b/Server/src/main/java/net/simon987/server/assembly/instruction/PushfInstruction.java
new file mode 100644
index 0000000..efa54ca
--- /dev/null
+++ b/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;
+    }
+}