From 7e8ee5ed9cad6484e9f13f81731b102ced58402e Mon Sep 17 00:00:00 2001
From: Adam Carpenter <gitlab@53hor.net>
Date: Tue, 9 Jul 2019 15:14:04 -0400
Subject: Init.

---
 meap/meap-code/ch5/ch5-cpu3/src/main.rs | 88 +++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100755 meap/meap-code/ch5/ch5-cpu3/src/main.rs

(limited to 'meap/meap-code/ch5/ch5-cpu3/src/main.rs')

diff --git a/meap/meap-code/ch5/ch5-cpu3/src/main.rs b/meap/meap-code/ch5/ch5-cpu3/src/main.rs
new file mode 100755
index 0000000..903ef23
--- /dev/null
+++ b/meap/meap-code/ch5/ch5-cpu3/src/main.rs
@@ -0,0 +1,88 @@
+struct CPU {
+    registers: [u8; 16],
+    position_in_memory: usize,
+    memory: [u8; 4096],
+    stack: [u16; 16], 
+    stack_pointer: usize,
+}
+
+impl CPU {
+    fn run(&mut self) {
+        loop {
+            let op_byte1 = self.memory[self.position_in_memory] as u16;
+            let op_byte2 = self.memory[self.position_in_memory + 1] as u16;
+            let opcode = op_byte1 << 8 | op_byte2;
+
+            let x  =       ((opcode & 0x0F00) >>  8) as u8; 
+            let y  =       ((opcode & 0x00F0) >>  4) as u8;
+            let op_minor =  (opcode & 0x000F) as u8;
+            let addr =       opcode & 0x0FFF;
+
+            self.position_in_memory += 2;
+
+            match opcode {
+                0x0000 => { return; },
+                0x00EE => { self.ret(); },
+                0x2000...0x2FFF => { self.call(addr); },
+                0x8000...0x8FFF => {
+                    match op_minor {
+                        4 => { self.add_xy(x, y); }
+                        _ => { unimplemented!("opcode: {:04x}", opcode); },
+                    }
+                },
+                _ => unimplemented!("opcode {:04x}", opcode),
+            }
+        }
+    }
+
+    fn call(&mut self, addr: u16) {
+        let sp = self.stack_pointer;
+        let stack = &mut self.stack;
+
+        if sp > stack.len() {
+            panic!("Stack overflow!")
+        }
+
+        stack[sp] = self.position_in_memory as u16;
+        self.stack_pointer += 1;
+        self.position_in_memory = addr as usize;
+    }
+    fn ret(&mut self) {
+        if self.stack_pointer == 0 {
+            panic!("Stack underflow");
+        }
+
+        self.stack_pointer -= 1;
+        self.position_in_memory = self.stack[self.stack_pointer] as usize;
+    }
+
+    fn add_xy(&mut self, x: u8, y: u8) {
+        self.registers[x as usize] += self.registers[y as usize];
+    }
+}
+
+fn main() {
+    let mut cpu = CPU {
+        registers: [0; 16],
+        memory: [0; 4096],
+        position_in_memory: 0,
+        stack: [0; 16],
+        stack_pointer: 0,
+    };
+
+    cpu.registers[0] = 5;
+    cpu.registers[1] = 10;
+
+    cpu.memory[0x000] = 0x21; cpu.memory[0x001] = 0x00; 
+    cpu.memory[0x002] = 0x21; cpu.memory[0x003] = 0x00;
+
+    cpu.memory[0x100] = 0x80; cpu.memory[0x101] = 0x14; 
+    cpu.memory[0x102] = 0x80; cpu.memory[0x103] = 0x14;
+    cpu.memory[0x104] = 0x00; cpu.memory[0x105] = 0xEE;
+
+    cpu.run();
+
+    assert_eq!(cpu.registers[0], 45);
+
+    println!("5 + (10 * 2) + (10 * 2) = {}", cpu.registers[0]);
+}
\ No newline at end of file
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