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use crate::instructions::Instruction;
use crate::memory::Memory;
#[derive(Default, Debug)]
pub struct CPU {
pub a: u8,
pub b: u8,
pub c: u8,
pub d: u8,
pub pc: u16,
pub sp: u16,
pub zero: bool,
pub carry: bool,
pub halted: bool,
}
impl CPU {
pub fn step(&mut self, mem: &mut Memory) {
let opcode = mem.read(self.pc);
self.inc_pc();
match opcode {
x if x == Instruction::MOV as u8 => self.mov(mem),
x if x == Instruction::ADD as u8 => self.add(mem),
x if x == Instruction::SUB as u8 => self.sub(mem),
x if x == Instruction::JMP as u8 => self.jmp(mem),
x if x == Instruction::JZ as u8 => self.jz(mem),
x if x == Instruction::JNZ as u8 => self.jnz(mem),
x if x == Instruction::HLT as u8 => self.halt(),
_ => panic!("Unknown opcode {:02X}", opcode),
}
}
pub fn inc_pc(&mut self) {
self.pc += 1;
}
pub fn halt(&mut self) {
self.halted = true;
}
pub fn mov(&mut self, mem: &Memory) {
let reg = mem.read(self.pc);
self.inc_pc();
let val = mem.read(self.pc);
self.inc_pc();
match reg {
0 => self.a = val,
1 => self.b = val,
2 => self.c = val,
3 => self.d = val,
_ => {}
}
self.zero = val == 0;
}
pub fn add(&mut self, mem: &Memory) {
let dest = mem.read(self.pc);
self.pc += 1;
let src = mem.read(self.pc);
self.pc += 1;
let (result, carry) = match (dest, src) {
(0, 0) => self.a.overflowing_add(self.a),
(0, 1) => self.a.overflowing_add(self.b),
(0, 2) => self.a.overflowing_add(self.c),
(0, 3) => self.a.overflowing_add(self.d),
(1, 0) => self.b.overflowing_add(self.a),
(1, 1) => self.b.overflowing_add(self.b),
(1, 2) => self.b.overflowing_add(self.c),
(1, 3) => self.b.overflowing_add(self.d),
(2, 0) => self.c.overflowing_add(self.a),
(2, 1) => self.c.overflowing_add(self.b),
(2, 2) => self.c.overflowing_add(self.c),
(2, 3) => self.c.overflowing_add(self.d),
(3, 0) => self.d.overflowing_add(self.a),
(3, 1) => self.d.overflowing_add(self.b),
(3, 2) => self.d.overflowing_add(self.c),
(3, 3) => self.d.overflowing_add(self.d),
_ => (0, false),
};
match dest {
0 => self.a = result,
1 => self.b = result,
2 => self.c = result,
3 => self.d = result,
_ => {}
}
self.zero = result == 0;
self.carry = carry;
}
pub fn sub(&mut self, mem: &Memory) {
let dest = mem.read(self.pc);
self.pc += 1;
let src = mem.read(self.pc);
self.pc += 1;
let (result, borrow) = match (dest, src) {
(0, 0) => self.a.overflowing_sub(self.a),
(0, 1) => self.a.overflowing_sub(self.b),
(0, 2) => self.a.overflowing_sub(self.c),
(0, 3) => self.a.overflowing_sub(self.d),
(1, 0) => self.b.overflowing_sub(self.a),
(1, 1) => self.b.overflowing_sub(self.b),
(1, 2) => self.b.overflowing_sub(self.c),
(1, 3) => self.b.overflowing_sub(self.d),
(2, 0) => self.c.overflowing_sub(self.a),
(2, 1) => self.c.overflowing_sub(self.b),
(2, 2) => self.c.overflowing_sub(self.c),
(2, 3) => self.c.overflowing_sub(self.d),
(3, 0) => self.d.overflowing_sub(self.a),
(3, 1) => self.d.overflowing_sub(self.b),
(3, 2) => self.d.overflowing_sub(self.c),
(3, 3) => self.d.overflowing_sub(self.d),
_ => (0, false),
};
match dest {
0 => self.a = result,
1 => self.b = result,
2 => self.c = result,
3 => self.d = result,
_ => {}
}
self.zero = result == 0;
self.carry = borrow;
}
pub fn jmp(&mut self, mem: &Memory) {
let low = mem.read(self.pc) as u16;
self.inc_pc();
let high = mem.read(self.pc) as u16;
self.inc_pc();
let addrs = (high << 8) | low;
self.pc = addrs;
}
pub fn jz(&mut self, mem: &Memory) {
let low = mem.read(self.pc) as u16;
self.inc_pc();
let high = mem.read(self.pc) as u16;
self.inc_pc();
let addrs = (high << 8) | low;
if self.zero {
self.pc = addrs;
}
}
pub fn jnz(&mut self, mem: &Memory) {
let low = mem.read(self.pc) as u16;
self.inc_pc();
let high = mem.read(self.pc) as u16;
self.inc_pc();
let addrs = (high << 8) | low;
if !self.zero {
self.pc = addrs;
}
}
}
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