inst.rs

    let byte = cpu.mmu.read(hl);
    let value = set(byte, 5);
    cpu.mmu.write(hl, value);
}

fn set_5_a(cpu: &mut Cpu) {
    cpu.a = set(cpu.a, 5);
}

fn set_6_b(cpu: &mut Cpu) {
    cpu.b = set(cpu.b, 6);
}

fn set_6_c(cpu: &mut Cpu) {
    cpu.c = set(cpu.c, 6);
}

fn set_6_d(cpu: &mut Cpu) {
    cpu.d = set(cpu.d, 6);
}

fn set_6_e(cpu: &mut Cpu) {
    cpu.e = set(cpu.e, 6);
}

fn set_6_h(cpu: &mut Cpu) {
    cpu.h = set(cpu.h, 6);
}

fn set_6_l(cpu: &mut Cpu) {
    cpu.l = set(cpu.l, 6);
}

fn set_6_mhl(cpu: &mut Cpu) {
    let hl = cpu.hl();
    let byte = cpu.mmu.read(hl);
    let value = set(byte, 6);
    cpu.mmu.write(hl, value);
}

fn set_6_a(cpu: &mut Cpu) {
    cpu.a = set(cpu.a, 6);
}

fn set_7_b(cpu: &mut Cpu) {
    cpu.b = set(cpu.b, 7);
}

fn set_7_c(cpu: &mut Cpu) {
    cpu.c = set(cpu.c, 7);
}

fn set_7_d(cpu: &mut Cpu) {
    cpu.d = set(cpu.d, 7);
}

fn set_7_e(cpu: &mut Cpu) {
    cpu.e = set(cpu.e, 7);
}

fn set_7_h(cpu: &mut Cpu) {
    cpu.h = set(cpu.h, 7);
}

fn set_7_l(cpu: &mut Cpu) {
    cpu.l = set(cpu.l, 7);
}

fn set_7_mhl(cpu: &mut Cpu) {
    let hl = cpu.hl();
    let byte = cpu.mmu.read(hl);
    let value = set(byte, 7);
    cpu.mmu.write(hl, value);
}

fn set_7_a(cpu: &mut Cpu) {
    cpu.a = set(cpu.a, 7);
}
/// Helper function to set one bit in a u8.
fn set(value: u8, bit: u8) -> u8 {
    value | (1u8 << (bit as usize))
}

/// Helper function to clear one bit in a u8
fn res(value: u8, bit: u8) -> u8 {
    value & !(1u8 << (bit as usize))
}

/// Helper function that rotates (shifts) left the given
/// byte (probably from a register) and updates the
/// proper flag registers.
fn rl(cpu: &mut Cpu, value: u8) -> u8 {
    let carry = cpu.get_carry();

    cpu.set_carry(value & 0x80 == 0x80);

    let result = (value << 1) | carry as u8;

    cpu.set_sub(false);
    cpu.set_zero(result == 0);
    cpu.set_half_carry(false);

    result
}

fn rlc(cpu: &mut Cpu, value: u8) -> u8 {
    cpu.set_carry(value & 0x80 == 0x80);

    let result = (value << 1) | (value >> 7);

    cpu.set_sub(false);
    cpu.set_zero(result == 0);
    cpu.set_half_carry(false);

    result
}

/// Helper function that rotates (shifts) right the given
/// byte (probably from a register) and updates the
/// proper flag registers.
fn rr(cpu: &mut Cpu, value: u8) -> u8 {
    let carry = cpu.get_carry();

    cpu.set_carry(value & 0x01 == 0x01);

    let result = (value >> 1) | ((carry as u8) << 7);

    cpu.set_sub(false);
    cpu.set_zero(result == 0);
    cpu.set_half_carry(false);

    result
}

fn rrc(cpu: &mut Cpu, value: u8) -> u8 {
    cpu.set_carry(value & 0x01 == 0x01);

    let result = (value >> 1) | (value << 7);

    cpu.set_sub(false);
    cpu.set_zero(result == 0);
    cpu.set_half_carry(false);

    result
}

/// Helper function to test one bit in a u8.
/// Returns true if bit is 0.
fn bit_zero(val: u8, bit: u8) -> bool {
    (val & (1u8 << (bit as usize))) == 0
}

fn bit_a(cpu: &mut Cpu, bit: u8) {
    cpu.set_sub(false);
    cpu.set_zero(bit_zero(cpu.a, bit));
    cpu.set_half_carry(true);
}

fn bit_b(cpu: &mut Cpu, bit: u8) {
    cpu.set_sub(false);
    cpu.set_zero(bit_zero(cpu.b, bit));
    cpu.set_half_carry(true);
}

fn bit_c(cpu: &mut Cpu, bit: u8) {
    cpu.set_sub(false);
    cpu.set_zero(bit_zero(cpu.c, bit));
    cpu.set_half_carry(true);
}

fn bit_d(cpu: &mut Cpu, bit: u8) {
    cpu.set_sub(false);
    cpu.set_zero(bit_zero(cpu.d, bit));
    cpu.set_half_carry(true);
}

fn bit_e(cpu: &mut Cpu, bit: u8) {
    cpu.set_sub(false);
    cpu.set_zero(bit_zero(cpu.e, bit));
    cpu.set_half_carry(true);
}

fn bit_h(cpu: &mut Cpu, bit: u8) {
    cpu.set_sub(false);
    cpu.set_zero(bit_zero(cpu.h, bit));
    cpu.set_half_carry(true);
}

fn bit_l(cpu: &mut Cpu, bit: u8) {
    cpu.set_sub(false);
    cpu.set_zero(bit_zero(cpu.l, bit));
    cpu.set_half_carry(true);
}

fn bit_mhl(cpu: &mut Cpu, bit: u8) {
    let byte = cpu.read_u8();
    cpu.set_sub(false);
    cpu.set_zero(bit_zero(byte, bit));
    cpu.set_half_carry(true);
}

fn add_set_flags(cpu: &mut Cpu, first: u8, second: u8) -> u8 {
    let first = first as u32;
    let second = second as u32;

    let result = first.wrapping_add(second);
    let result_b = result as u8;

    cpu.set_sub(false);
    cpu.set_zero(result_b == 0);
    cpu.set_half_carry((first ^ second ^ result) & 0x10 == 0x10);
    cpu.set_carry(result & 0x100 == 0x100);

    result_b
}

fn add_carry_set_flags(cpu: &mut Cpu, first: u8, second: u8) -> u8 {
    let first = first as u32;
    let second = second as u32;
    let carry = cpu.get_carry() as u32;

    let result = first.wrapping_add(second).wrapping_add(carry);
    let result_b = result as u8;

    cpu.set_sub(false);
    cpu.set_zero(result_b == 0);
    cpu.set_half_carry((first ^ second ^ result) & 0x10 == 0x10);
    cpu.set_carry(result & 0x100 == 0x100);

    result_b
}

fn sub_set_flags(cpu: &mut Cpu, first: u8, second: u8) -> u8 {
    let first = first as u32;
    let second = second as u32;

    let result = first.wrapping_sub(second);
    let result_b = result as u8;

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

    result_b
}

fn sub_carry_set_flags(cpu: &mut Cpu, first: u8, second: u8) -> u8 {
    let first = first as u32;
    let second = second as u32;
    let carry = cpu.get_carry() as u32;

    let result = first.wrapping_sub(second).wrapping_sub(carry);
    let result_b = result as u8;

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

    result_b
}

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

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

    result 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 to shift an `u8` to the left and update CPU
/// flags.
fn sla(cpu: &mut Cpu, value: u8) -> u8 {
    let result = value << 1;

    cpu.set_sub(false);
    cpu.set_zero(result == 0);
    cpu.set_half_carry(false);
    cpu.set_carry(value & 0x80 == 0x80);

    result
}

fn sra(cpu: &mut Cpu, value: u8) -> u8 {
    let result = (value >> 1) | (value & 0x80);

    cpu.set_sub(false);
    cpu.set_zero(result == 0);
    cpu.set_half_carry(false);
    cpu.set_carry(value & 0x01 == 0x01);

    result
}

fn srl(cpu: &mut Cpu, value: u8) -> u8 {
    let result = value >> 1;

    cpu.set_sub(false);
    cpu.set_zero(result == 0);
    cpu.set_half_carry(false);
    cpu.set_carry(value & 0x01 == 0x01);

    result
}

/// 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;
}