gb-emu/src/processor/mod.rs

use std::mem::transmute;

use crate::{verbose_println, Memory, State};

mod instructions;
mod opcodes;

#[derive(PartialEq)]
pub(crate) enum FLAGS {
    Zero = 7,
    NSubtract = 6,
    HalfCarry = 5,
    Carry = 4,
}

pub(crate) enum Direction {
    Left,
    Right,
}

pub struct CPU {
    pub memory: Memory,
    pub state: State,
    pub last_instruction: u8,
    pub last_instruction_addr: u16,
}

impl CPU {
    pub fn exec_next(&mut self) {
        unsafe { self.last_instruction_addr = self.state.pc.as_u16 };
        let opcode = self.next_opcode();
        self.last_instruction = opcode;
        verbose_println!(
            "exec {:#4X} from pc: {:#X}",
            opcode,
            self.last_instruction_addr
        );
        self.run_opcode(opcode);
    }

    fn next_opcode(&mut self) -> u8 {
        unsafe {
            let opcode = self.memory.get(self.state.pc.as_u16);
            self.state.pc.as_u16 = self.state.pc.as_u16.wrapping_add(0x1);
            return opcode;
        };
    }
}

fn as_signed(unsigned: u8) -> i8 {
    unsafe {
        return transmute(unsigned);
    }
}

fn get_bit(byte: u8, flag: u8) -> bool {
    let mask = 1 << flag;
    let got = byte & mask;
    return got > 0x0;
}

fn rotate(byte: u8, direction: &Direction) -> (u8, bool) {
    match direction {
        Direction::Left => {
            let carry = get_bit(byte, 7);
            let r = byte << 1;
            return (r, carry);
        }
        Direction::Right => {
            let carry = get_bit(byte, 0);
            let r = byte >> 1;
            return (r, carry);
        }
    }
}

fn get_rotation_carry(direction: &Direction) -> u8 {
    match direction {
        Direction::Left => 0b1,
        Direction::Right => 0b10000000,
    }
}

fn swap_nibbles(byte: u8) -> u8 {
    (byte & 0x0F) << 4 | (byte & 0xF0) >> 4
}

fn res(byte: u8, bit: u8) -> u8 {
    byte & !(1 << bit)
}

fn set(byte: u8, bit: u8) -> u8 {
    byte | (1 << bit)
}