nesemu/src/native_core/cpu/helpers.rs

use super::*;

impl Cpu6502 {
    pub(super) fn fetch<B: CpuBus>(&mut self, bus: &mut B) -> u8 {
        let value = bus.read(self.pc);
        self.pc = self.pc.wrapping_add(1);
        value
    }

    pub(super) fn fetch_u16<B: CpuBus>(&mut self, bus: &mut B) -> u16 {
        let lo = self.fetch(bus) as u16;
        let hi = self.fetch(bus) as u16;
        (hi << 8) | lo
    }

    pub(super) fn read_u16<B: CpuBus>(&mut self, bus: &mut B, addr: u16) -> u16 {
        let lo = bus.read(addr) as u16;
        let hi = bus.read(addr.wrapping_add(1)) as u16;
        (hi << 8) | lo
    }

    pub(super) fn read_u16_bug<B: CpuBus>(&mut self, bus: &mut B, addr: u16) -> u16 {
        let lo = bus.read(addr) as u16;
        let hi_addr = (addr & 0xFF00) | (addr.wrapping_add(1) & 0x00FF);
        let hi = bus.read(hi_addr) as u16;
        (hi << 8) | lo
    }

    pub(super) fn addr_zp<B: CpuBus>(&mut self, bus: &mut B) -> u16 {
        self.fetch(bus) as u16
    }

    pub(super) fn addr_zpx<B: CpuBus>(&mut self, bus: &mut B) -> u16 {
        self.fetch(bus).wrapping_add(self.x) as u16
    }

    pub(super) fn addr_zpy<B: CpuBus>(&mut self, bus: &mut B) -> u16 {
        self.fetch(bus).wrapping_add(self.y) as u16
    }

    pub(super) fn addr_abs<B: CpuBus>(&mut self, bus: &mut B) -> u16 {
        self.fetch_u16(bus)
    }

    pub(super) fn addr_abx<B: CpuBus>(&mut self, bus: &mut B) -> u16 {
        self.addr_abx_cross(bus).0
    }

    pub(super) fn addr_aby<B: CpuBus>(&mut self, bus: &mut B) -> u16 {
        self.addr_aby_cross(bus).0
    }

    pub(super) fn addr_indx<B: CpuBus>(&mut self, bus: &mut B) -> u16 {
        let ptr = self.fetch(bus).wrapping_add(self.x);
        let lo = bus.read(ptr as u16) as u16;
        let hi = bus.read(ptr.wrapping_add(1) as u16) as u16;
        (hi << 8) | lo
    }

    pub(super) fn addr_indy<B: CpuBus>(&mut self, bus: &mut B) -> u16 {
        self.addr_indy_cross(bus).0
    }

    pub(super) fn addr_abx_cross<B: CpuBus>(&mut self, bus: &mut B) -> (u16, bool) {
        let base = self.fetch_u16(bus);
        let addr = base.wrapping_add(self.x as u16);
        (addr, (base & 0xFF00) != (addr & 0xFF00))
    }

    pub(super) fn addr_aby_cross<B: CpuBus>(&mut self, bus: &mut B) -> (u16, bool) {
        let base = self.fetch_u16(bus);
        let addr = base.wrapping_add(self.y as u16);
        (addr, (base & 0xFF00) != (addr & 0xFF00))
    }

    pub(super) fn addr_indy_cross<B: CpuBus>(&mut self, bus: &mut B) -> (u16, bool) {
        let ptr = self.fetch(bus);
        let lo = bus.read(ptr as u16) as u16;
        let hi = bus.read(ptr.wrapping_add(1) as u16) as u16;
        let base = (hi << 8) | lo;
        let addr = base.wrapping_add(self.y as u16);
        (addr, (base & 0xFF00) != (addr & 0xFF00))
    }

    pub(super) fn read_zp<B: CpuBus>(&mut self, bus: &mut B) -> u8 {
        let addr = self.addr_zp(bus);
        bus.read(addr)
    }

    pub(super) fn read_zpx<B: CpuBus>(&mut self, bus: &mut B) -> u8 {
        let addr = self.addr_zpx(bus);
        bus.read(addr)
    }

    pub(super) fn read_zpy<B: CpuBus>(&mut self, bus: &mut B) -> u8 {
        let addr = self.addr_zpy(bus);
        bus.read(addr)
    }

    pub(super) fn read_abs<B: CpuBus>(&mut self, bus: &mut B) -> u8 {
        let addr = self.addr_abs(bus);
        bus.read(addr)
    }

    pub(super) fn read_abx_cross<B: CpuBus>(&mut self, bus: &mut B) -> (u8, bool) {
        let (addr, crossed) = self.addr_abx_cross(bus);
        (bus.read(addr), crossed)
    }

    pub(super) fn read_aby_cross<B: CpuBus>(&mut self, bus: &mut B) -> (u8, bool) {
        let (addr, crossed) = self.addr_aby_cross(bus);
        (bus.read(addr), crossed)
    }

    pub(super) fn read_indx<B: CpuBus>(&mut self, bus: &mut B) -> u8 {
        let addr = self.addr_indx(bus);
        bus.read(addr)
    }

    pub(super) fn read_indy_cross<B: CpuBus>(&mut self, bus: &mut B) -> (u8, bool) {
        let (addr, crossed) = self.addr_indy_cross(bus);
        (bus.read(addr), crossed)
    }

    pub(super) fn push<B: CpuBus>(&mut self, bus: &mut B, value: u8) {
        let addr = 0x0100 | self.sp as u16;
        bus.write(addr, value);
        self.sp = self.sp.wrapping_sub(1);
    }

    pub(super) fn pop<B: CpuBus>(&mut self, bus: &mut B) -> u8 {
        self.sp = self.sp.wrapping_add(1);
        let addr = 0x0100 | self.sp as u16;
        bus.read(addr)
    }

    pub(super) fn set_zn(&mut self, value: u8) {
        if value == 0 {
            self.p |= FLAG_ZERO;
        } else {
            self.p &= !FLAG_ZERO;
        }
        if (value & 0x80) != 0 {
            self.p |= FLAG_NEGATIVE;
        } else {
            self.p &= !FLAG_NEGATIVE;
        }
    }

    pub(super) fn set_flag(&mut self, mask: u8, enabled: bool) {
        if enabled {
            self.p |= mask;
        } else {
            self.p &= !mask;
        }
    }

    pub(super) fn compare(&mut self, lhs: u8, rhs: u8) {
        let result = lhs.wrapping_sub(rhs);
        self.set_flag(FLAG_CARRY, lhs >= rhs);
        self.set_zn(result);
    }

    pub(super) fn bit(&mut self, value: u8) {
        self.set_flag(FLAG_ZERO, (self.a & value) == 0);
        self.set_flag(FLAG_OVERFLOW, (value & 0x40) != 0);
        self.set_flag(FLAG_NEGATIVE, (value & 0x80) != 0);
    }

    pub(super) fn adc(&mut self, value: u8) {
        let carry = u16::from((self.p & FLAG_CARRY) != 0);
        let a = self.a as u16;
        let b = value as u16;
        let sum = a + b + carry;
        let result = sum as u8;

        self.set_flag(FLAG_CARRY, sum > 0xFF);
        let overflow = ((self.a ^ result) & (value ^ result) & 0x80) != 0;
        self.set_flag(FLAG_OVERFLOW, overflow);

        self.a = result;
        self.set_zn(self.a);
    }

    pub(super) fn asl(&mut self, value: u8) -> u8 {
        self.set_flag(FLAG_CARRY, (value & 0x80) != 0);
        let out = value << 1;
        self.set_zn(out);
        out
    }

    pub(super) fn lsr(&mut self, value: u8) -> u8 {
        self.set_flag(FLAG_CARRY, (value & 0x01) != 0);
        let out = value >> 1;
        self.set_zn(out);
        out
    }

    pub(super) fn rol(&mut self, value: u8) -> u8 {
        let carry_in = u8::from((self.p & FLAG_CARRY) != 0);
        self.set_flag(FLAG_CARRY, (value & 0x80) != 0);
        let out = (value << 1) | carry_in;
        self.set_zn(out);
        out
    }

    pub(super) fn ror(&mut self, value: u8) -> u8 {
        let carry_in = if (self.p & FLAG_CARRY) != 0 { 0x80 } else { 0 };
        self.set_flag(FLAG_CARRY, (value & 0x01) != 0);
        let out = (value >> 1) | carry_in;
        self.set_zn(out);
        out
    }

    pub(super) fn branch<B: CpuBus>(&mut self, bus: &mut B, condition: bool) -> u8 {
        let offset = self.fetch(bus) as i8;
        if !condition {
            return 2;
        }
        let old_pc = self.pc;
        self.pc = self.pc.wrapping_add_signed(offset as i16);
        if (old_pc & 0xFF00) != (self.pc & 0xFF00) {
            4
        } else {
            3
        }
    }

    pub(super) fn service_interrupt<B: CpuBus>(
        &mut self,
        bus: &mut B,
        vector_addr: u16,
        break_flag: bool,
    ) {
        self.push(bus, (self.pc >> 8) as u8);
        self.push(bus, self.pc as u8);
        let mut status = (self.p | FLAG_UNUSED) & !FLAG_BREAK;
        if break_flag {
            status |= FLAG_BREAK;
        }
        self.push(bus, status);
        self.p = (self.p | FLAG_IRQ_DISABLE | FLAG_UNUSED) & !FLAG_BREAK;
        self.pc = self.read_u16(bus, vector_addr);
    }
}