inst.rs

    cpu.set_sub(true);
    cpu.set_zero(value_b == 0);
    cpu.set_half_carry((first ^ second ^ value) & 0x10 == 0x10);
    cpu.set_carry(value & 0x100 == 0x100);

    value_b
}

fn add_u16_u16(cpu: &mut Cpu, first: u16, second: u16) -> u16 {
    let first = first as u32;
    let second = second as u32;
    let value = first.wrapping_add(second);

    cpu.set_sub(false);
    cpu.set_half_carry((first ^ second ^ value) & 0x1000 == 0x1000);
    cpu.set_carry(value & 0x10000 == 0x10000);

    value as u16
}

fn swap(cpu: &mut Cpu, value: u8) -> u8 {
    cpu.set_sub(false);
    cpu.set_zero(value == 0);
    cpu.set_half_carry(false);
    cpu.set_carry(false);

    (value << 4) | (value >> 4)
}

/// Helper function for RST instructions, pushes the
/// current PC to the stack and jumps to the provided
/// address.
fn rst(cpu: &mut Cpu, addr: u16) {
    cpu.push_word(cpu.pc);
    cpu.pc = addr;
}