From 67cdcc2e12118becb823e20a40cc2687f2b8425a Mon Sep 17 00:00:00 2001
From: Adam Carpenter <53hornet@gmail.com>
Date: Wed, 27 Mar 2019 15:32:37 -0400
Subject: Started Rust in Action MEAP.

---
 meap/meap-code/ch5/ch5-cpu2/src/main.rs | 60 +++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)
 create mode 100644 meap/meap-code/ch5/ch5-cpu2/src/main.rs

(limited to 'meap/meap-code/ch5/ch5-cpu2/src/main.rs')

diff --git a/meap/meap-code/ch5/ch5-cpu2/src/main.rs b/meap/meap-code/ch5/ch5-cpu2/src/main.rs
new file mode 100644
index 0000000..8271ca8
--- /dev/null
+++ b/meap/meap-code/ch5/ch5-cpu2/src/main.rs
@@ -0,0 +1,60 @@
+const HALT: u8 = 0x0;
+const ARITHMETIC_AND_LOGIC: u8 = 0x8;
+const ADD_XY: u8 = 0x4;
+
+struct CPU {
+    // current_operation: u16, // no longer needed
+    registers: [u8; 16], // increase number of registers to 16 (0..F), as per CHIP-8
+    position_in_memory: usize, // add a program counter.. using a usize to simplify array indexing
+    memory: [u8; 4096], // give the system 4kb memory
+}
+
+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 raw_op = op_byte1 << 8 | op_byte2;
+
+            self.position_in_memory += 2; 
+
+            let op_major = ((raw_op & 0xF000) >> 12) as u8;
+            let x  =       ((raw_op & 0x0F00) >>  8) as u8; 
+            let y  =       ((raw_op & 0x00F0) >>  4) as u8;
+            let op_minor =  (raw_op & 0x000F) as u8;
+        
+            match (op_major, op_minor) {
+                (HALT, HALT) => { return; },
+                (ARITHMETIC_AND_LOGIC, ADD_XY) => self.add_xy(x, y),
+                _ => unimplemented!("opcode {:04x}", raw_op), // this macro is useful when you are debugging, as it will promptly indicate that you have made a typo
+            }
+        }
+    }
+
+    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,
+    };
+
+    cpu.registers[0] = 5;
+    cpu.registers[1] = 10;
+    cpu.registers[2] = 10;  // initialise a few more registers
+    cpu.registers[3] = 10;  //
+
+    cpu.memory[0] = 0x80; cpu.memory[1] = 0x14; // 0x8014 -> ADD register 1 to register 0
+    cpu.memory[2] = 0x80; cpu.memory[3] = 0x24; // 0x8014 -> ADD register 2 to register 0
+    cpu.memory[4] = 0x80; cpu.memory[5] = 0x34; // 0x8014 -> ADD register 3 to register 0
+
+    cpu.run();
+
+    assert_eq!(cpu.registers[0], 35);
+
+    println!("5 + 10 + 10 + 10 = {}", cpu.registers[0]);
+}
-- 
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