inst.rs

fn ld_c_d(cpu: &mut Cpu) {
    cpu.c = cpu.d;
}

fn ld_c_e(cpu: &mut Cpu) {
    cpu.c = cpu.e;
}

fn ld_c_h(cpu: &mut Cpu) {
    cpu.c = cpu.h;
}

fn ld_c_l(cpu: &mut Cpu) {
    cpu.c = cpu.l;
}

fn ld_c_mhl(cpu: &mut Cpu) {
    let byte = cpu.mmu.read(cpu.hl());
    cpu.c = byte;
}

fn ld_c_a(cpu: &mut Cpu) {
    cpu.c = cpu.a;
}

fn ld_d_b(cpu: &mut Cpu) {
    cpu.d = cpu.b;
}

fn ld_d_c(cpu: &mut Cpu) {
    cpu.d = cpu.c;
}

fn ld_d_d(cpu: &mut Cpu) {
    cpu.d = cpu.d;
}

fn ld_d_e(cpu: &mut Cpu) {
    cpu.d = cpu.e;
}

fn ld_d_h(cpu: &mut Cpu) {
    cpu.d = cpu.h;
}

fn ld_d_l(cpu: &mut Cpu) {
    cpu.d = cpu.l;
}

fn ld_d_mhl(cpu: &mut Cpu) {
    let byte = cpu.mmu.read(cpu.hl());
    cpu.d = byte;
}

fn ld_d_a(cpu: &mut Cpu) {
    cpu.d = cpu.a;
}

fn ld_e_b(cpu: &mut Cpu) {
    cpu.e = cpu.b;
}

fn ld_e_c(cpu: &mut Cpu) {
    cpu.e = cpu.c;
}

fn ld_e_d(cpu: &mut Cpu) {
    cpu.e = cpu.d;
}

fn ld_e_e(cpu: &mut Cpu) {
    cpu.e = cpu.e;
}

fn ld_e_h(cpu: &mut Cpu) {
    cpu.e = cpu.h;
}

fn ld_e_l(cpu: &mut Cpu) {
    cpu.e = cpu.l;
}

fn ld_e_mhl(cpu: &mut Cpu) {
    let byte = cpu.mmu.read(cpu.hl());
    cpu.e = byte;
}

fn ld_e_a(cpu: &mut Cpu) {
    cpu.e = cpu.a;
}

fn ld_h_b(cpu: &mut Cpu) {
    cpu.h = cpu.b;
}

fn ld_h_c(cpu: &mut Cpu) {
    cpu.h = cpu.c;
}

fn ld_h_d(cpu: &mut Cpu) {
    cpu.h = cpu.d;
}

fn ld_h_e(cpu: &mut Cpu) {
    cpu.h = cpu.e;
}

fn ld_h_h(cpu: &mut Cpu) {
    cpu.h = cpu.h;
}

fn ld_h_l(cpu: &mut Cpu) {
    cpu.h = cpu.l;
}

fn ld_h_mhl(cpu: &mut Cpu) {
    let byte = cpu.mmu.read(cpu.hl());
    cpu.h = byte;
}

fn ld_h_a(cpu: &mut Cpu) {
    cpu.h = cpu.a;
}

fn ld_l_b(cpu: &mut Cpu) {
    cpu.l = cpu.b;
}

fn ld_l_c(cpu: &mut Cpu) {
    cpu.l = cpu.c;
}

fn ld_l_d(cpu: &mut Cpu) {
    cpu.l = cpu.d;
}

fn ld_l_e(cpu: &mut Cpu) {
    cpu.l = cpu.e;
}

fn ld_l_h(cpu: &mut Cpu) {
    cpu.l = cpu.h;
}

fn ld_l_l(cpu: &mut Cpu) {
    cpu.l = cpu.l;
}

fn ld_l_mhl(cpu: &mut Cpu) {
    let byte = cpu.mmu.read(cpu.hl());
    cpu.l = byte;
}

fn ld_l_a(cpu: &mut Cpu) {
    cpu.l = cpu.a;
}

fn ld_mhl_b(cpu: &mut Cpu) {
    cpu.mmu.write(cpu.hl(), cpu.b);
}

fn ld_mhl_c(cpu: &mut Cpu) {
    cpu.mmu.write(cpu.hl(), cpu.c);
}

fn ld_mhl_d(cpu: &mut Cpu) {
    cpu.mmu.write(cpu.hl(), cpu.d);
}

fn ld_mhl_e(cpu: &mut Cpu) {
    cpu.mmu.write(cpu.hl(), cpu.e);
}

fn ld_mhl_h(cpu: &mut Cpu) {
    cpu.mmu.write(cpu.hl(), cpu.h);
}

fn ld_mhl_l(cpu: &mut Cpu) {
    cpu.mmu.write(cpu.hl(), cpu.l);
}

fn halt(cpu: &mut Cpu) {
    cpu.halt();
}

fn ld_mhl_a(cpu: &mut Cpu) {
    cpu.mmu.write(cpu.hl(), cpu.a);
}

fn ld_a_b(cpu: &mut Cpu) {
    cpu.a = cpu.b;
}

fn ld_a_c(cpu: &mut Cpu) {
    cpu.a = cpu.c;
}

fn ld_a_d(cpu: &mut Cpu) {
    cpu.a = cpu.d;
}

fn ld_a_e(cpu: &mut Cpu) {
    cpu.a = cpu.e;
}

fn ld_a_h(cpu: &mut Cpu) {
    cpu.a = cpu.h;
}

fn ld_a_l(cpu: &mut Cpu) {
    cpu.a = cpu.l;
}

fn ld_a_mhl(cpu: &mut Cpu) {
    let byte = cpu.mmu.read(cpu.hl());
    cpu.a = byte;
}

fn ld_a_a(cpu: &mut Cpu) {
    cpu.a = cpu.a;
}

fn add_a_b(cpu: &mut Cpu) {
    cpu.a = add_set_flags(cpu, cpu.a, cpu.b);
}

fn add_a_c(cpu: &mut Cpu) {
    cpu.a = add_set_flags(cpu, cpu.a, cpu.c);
}

fn add_a_d(cpu: &mut Cpu) {
    cpu.a = add_set_flags(cpu, cpu.a, cpu.d);
}

fn add_a_e(cpu: &mut Cpu) {
    cpu.a = add_set_flags(cpu, cpu.a, cpu.e);
}

fn add_a_h(cpu: &mut Cpu) {
    cpu.a = add_set_flags(cpu, cpu.a, cpu.h);
}

fn add_a_l(cpu: &mut Cpu) {
    cpu.a = add_set_flags(cpu, cpu.a, cpu.l);
}

fn add_a_mhl(cpu: &mut Cpu) {
    let byte = cpu.mmu.read(cpu.hl());
    cpu.a = add_set_flags(cpu, cpu.a, byte);
}

fn add_a_a(cpu: &mut Cpu) {
    cpu.a = add_set_flags(cpu, cpu.a, cpu.a);
}

fn sub_a_b(cpu: &mut Cpu) {
    cpu.a = sub_set_flags(cpu, cpu.a, cpu.b);
}

fn sub_a_a(cpu: &mut Cpu) {
    cpu.a = sub_set_flags(cpu, cpu.a, cpu.a);
}

fn and_a_b(cpu: &mut Cpu) {
    cpu.a &= cpu.b;

    cpu.set_sub(false);
    cpu.set_zero(cpu.a == 0);
    cpu.set_half_carry(true);
    cpu.set_carry(false);
}

fn and_a_c(cpu: &mut Cpu) {
    cpu.a &= cpu.c;

    cpu.set_sub(false);
    cpu.set_zero(cpu.a == 0);
    cpu.set_half_carry(true);
    cpu.set_carry(false);
}

fn and_a_d(cpu: &mut Cpu) {
    cpu.a &= cpu.d;

    cpu.set_sub(false);
    cpu.set_zero(cpu.a == 0);
    cpu.set_half_carry(true);
    cpu.set_carry(false);
}

fn and_a_e(cpu: &mut Cpu) {
    cpu.a &= cpu.e;

    cpu.set_sub(false);
    cpu.set_zero(cpu.a == 0);
    cpu.set_half_carry(true);
    cpu.set_carry(false);
}

fn and_a_h(cpu: &mut Cpu) {
    cpu.a &= cpu.h;

    cpu.set_sub(false);
    cpu.set_zero(cpu.a == 0);
    cpu.set_half_carry(true);
    cpu.set_carry(false);
}

fn and_a_l(cpu: &mut Cpu) {
    cpu.a &= cpu.l;

    cpu.set_sub(false);
    cpu.set_zero(cpu.a == 0);
    cpu.set_half_carry(true);
    cpu.set_carry(false);
}

fn and_a_mhl(cpu: &mut Cpu) {
    let byte = cpu.mmu.read(cpu.hl());
    cpu.a &= byte;

    cpu.set_sub(false);
    cpu.set_zero(cpu.a == 0);
    cpu.set_half_carry(true);
    cpu.set_carry(false);
}

fn and_a_a(cpu: &mut Cpu) {
    cpu.a &= cpu.a;

    cpu.set_sub(false);
    cpu.set_zero(cpu.a == 0);
    cpu.set_half_carry(true);
    cpu.set_carry(false);
}

fn xor_a_c(cpu: &mut Cpu) {
    cpu.a ^= cpu.c;

    cpu.set_sub(false);
    cpu.set_zero(cpu.a == 0);
    cpu.set_half_carry(false);
    cpu.set_carry(false);
}

fn xor_a_l(cpu: &mut Cpu) {
    cpu.a ^= cpu.l;

    cpu.set_sub(false);
    cpu.set_zero(cpu.a == 0);
    cpu.set_half_carry(false);
    cpu.set_carry(false);
}

fn xor_a_mhl(cpu: &mut Cpu) {
    let byte = cpu.mmu.read(cpu.hl());
    cpu.a ^= byte;

    cpu.set_sub(false);
    cpu.set_zero(cpu.a == 0);
    cpu.set_half_carry(false);
    cpu.set_carry(false);
}

fn xor_a_a(cpu: &mut Cpu) {
    cpu.a ^= cpu.a;

    cpu.set_sub(false);
    cpu.set_zero(cpu.a == 0);
    cpu.set_half_carry(false);
    cpu.set_carry(false);
}

fn or_a_b(cpu: &mut Cpu) {
    cpu.a |= cpu.b;

    cpu.set_sub(false);
    cpu.set_zero(cpu.a == 0);
    cpu.set_half_carry(false);
    cpu.set_carry(false);
}

fn or_a_c(cpu: &mut Cpu) {
    cpu.a |= cpu.c;

    cpu.set_sub(false);
    cpu.set_zero(cpu.a == 0);
    cpu.set_half_carry(false);
    cpu.set_carry(false);
}

fn or_a_mhl(cpu: &mut Cpu) {
    let byte = cpu.mmu.read(cpu.hl());
    cpu.a |= byte;

    cpu.set_sub(false);
    cpu.set_zero(cpu.a == 0);
    cpu.set_half_carry(false);
    cpu.set_carry(false);
}

fn or_a_a(cpu: &mut Cpu) {
    cpu.a |= cpu.a;

    cpu.set_sub(false);
    cpu.set_zero(cpu.a == 0);
    cpu.set_half_carry(false);
    cpu.set_carry(false);
}

fn cp_a_b(cpu: &mut Cpu) {
    sub_set_flags(cpu, cpu.a, cpu.b);
}

fn cp_a_c(cpu: &mut Cpu) {
    sub_set_flags(cpu, cpu.a, cpu.c);
}

fn cp_a_d(cpu: &mut Cpu) {
    sub_set_flags(cpu, cpu.a, cpu.d);
}

fn cp_a_e(cpu: &mut Cpu) {
    sub_set_flags(cpu, cpu.a, cpu.e);
}

fn cp_a_h(cpu: &mut Cpu) {
    sub_set_flags(cpu, cpu.a, cpu.h);
}

fn cp_a_l(cpu: &mut Cpu) {
    sub_set_flags(cpu, cpu.a, cpu.l);
}

fn cp_a_mhl(cpu: &mut Cpu) {
    let byte = cpu.mmu.read(cpu.hl());
    sub_set_flags(cpu, cpu.a, byte);
}

fn cp_a_a(cpu: &mut Cpu) {
    sub_set_flags(cpu, cpu.a, cpu.a);
}

fn ret_nz(cpu: &mut Cpu) {
    if cpu.get_zero() {
        return;
    }

    cpu.pc = cpu.pop_word();
    cpu.ticks = cpu.ticks.wrapping_add(12);
}

fn pop_bc(cpu: &mut Cpu) {
    let word = cpu.pop_word();
    cpu.set_bc(word);
}

fn jp_nz_u16(cpu: &mut Cpu) {
    let word = cpu.read_u16();

    if cpu.get_zero() {
        return;
    }

    cpu.pc = word;
    cpu.ticks = cpu.ticks.wrapping_add(4);
}

fn jp_u16(cpu: &mut Cpu) {
    let word = cpu.read_u16();
    cpu.pc = word;
}

fn call_nz_u16(cpu: &mut Cpu) {
    let word = cpu.read_u16();

    if cpu.get_zero() {
        return;
    }

    cpu.push_word(cpu.pc);
    cpu.pc = word;
    cpu.ticks = cpu.ticks.wrapping_add(12);
}

fn push_bc(cpu: &mut Cpu) {
    cpu.push_word(cpu.bc());
}

fn add_a_u8(cpu: &mut Cpu) {
    let byte = cpu.read_u8();
    cpu.a = add_set_flags(cpu, cpu.a, byte);
}

fn rst_00h(cpu: &mut Cpu) {
    rst(cpu, 0x0000);
}

fn ret_z(cpu: &mut Cpu) {
    if !cpu.get_zero() {
        return;
    }

    cpu.pc = cpu.pop_word();
    cpu.ticks = cpu.ticks.wrapping_add(12);
}

fn ret(cpu: &mut Cpu) {
    cpu.pc = cpu.pop_word();
}

fn jp_z_u16(cpu: &mut Cpu) {
    let word = cpu.read_u16();

    if !cpu.get_zero() {
        return;
    }

    cpu.pc = word;
    cpu.ticks = cpu.ticks.wrapping_add(4);
}

fn call_z_u16(cpu: &mut Cpu) {
    let word = cpu.read_u16();

    if !cpu.get_zero() {
        return;
    }

    cpu.push_word(cpu.pc);
    cpu.pc = word;
    cpu.ticks = cpu.ticks.wrapping_add(12);
}

fn call_u16(cpu: &mut Cpu) {
    let word = cpu.read_u16();
    cpu.push_word(cpu.pc);
    cpu.pc = word;
}

fn adc_a_u8(cpu: &mut Cpu) {
    let byte = cpu.read_u8();
    cpu.a = add_carry_set_flags(cpu, cpu.a, byte);
}

fn rst_08h(cpu: &mut Cpu) {
    rst(cpu, 0x0008);
}

fn ret_nc(cpu: &mut Cpu) {
    if cpu.get_carry() {
        return;
    }

    cpu.pc = cpu.pop_word();
    cpu.ticks = cpu.ticks.wrapping_add(12);
}

fn pop_de(cpu: &mut Cpu) {
    let word = cpu.pop_word();
    cpu.set_de(word);
}

fn jp_nc_u16(cpu: &mut Cpu) {
    let word = cpu.read_u16();

    if cpu.get_carry() {
        return;
    }

    cpu.pc = word;
    cpu.ticks = cpu.ticks.wrapping_add(4);
}

fn call_nc_u16(cpu: &mut Cpu) {
    let word = cpu.read_u16();

    if cpu.get_carry() {
        return;
    }

    cpu.push_word(cpu.pc);
    cpu.pc = word;
    cpu.ticks = cpu.ticks.wrapping_add(12);
}

fn push_de(cpu: &mut Cpu) {
    cpu.push_word(cpu.de());
}

fn sub_a_u8(cpu: &mut Cpu) {
    let byte = cpu.read_u8();
    cpu.a = sub_set_flags(cpu, cpu.a, byte);
}

fn rst_10h(cpu: &mut Cpu) {
    rst(cpu, 0x0010);
}

fn ret_c(cpu: &mut Cpu) {
    if !cpu.get_carry() {
        return;
    }

    cpu.pc = cpu.pop_word();
    cpu.ticks = cpu.ticks.wrapping_add(12);
}

fn reti(cpu: &mut Cpu) {
    cpu.pc = cpu.pop_word();
    cpu.enable_int();
}

fn jp_c_u16(cpu: &mut Cpu) {
    let word = cpu.read_u16();

    if !cpu.get_carry() {
        return;
    }

    cpu.pc = word;
    cpu.ticks = cpu.ticks.wrapping_add(4);
}

fn call_c_u16(cpu: &mut Cpu) {
    let word = cpu.read_u16();

    if !cpu.get_carry() {
        return;
    }

    cpu.push_word(cpu.pc);
    cpu.pc = word;
    cpu.ticks = cpu.ticks.wrapping_add(12);
}

fn rst_18h(cpu: &mut Cpu) {
    rst(cpu, 0x0018);
}

fn ld_mff00u8_a(cpu: &mut Cpu) {
    let byte = cpu.read_u8();
    cpu.mmu.write(0xff00 + byte as u16, cpu.a);
}

fn pop_hl(cpu: &mut Cpu) {
    let word = cpu.pop_word();
    cpu.set_hl(word);
}

fn ld_mff00c_a(cpu: &mut Cpu) {
    cpu.mmu.write(0xff00 + cpu.c as u16, cpu.a);
}

fn push_hl(cpu: &mut Cpu) {
    cpu.push_word(cpu.hl());
}

fn and_a_u8(cpu: &mut Cpu) {
    let byte = cpu.read_u8();

    cpu.a &= byte;

    cpu.set_sub(false);
    cpu.set_zero(cpu.a == 0);
    cpu.set_half_carry(true);
    cpu.set_carry(false);
}

fn rst_20h(cpu: &mut Cpu) {
    rst(cpu, 0x0020);
}

fn jp_hl(cpu: &mut Cpu) {
    cpu.pc = cpu.hl();
}

fn ld_mu16_a(cpu: &mut Cpu) {
    let word = cpu.read_u16();
    cpu.mmu.write(word, cpu.a);
}

fn xor_a_u8(cpu: &mut Cpu) {
    let byte = cpu.read_u8();
    cpu.a ^= byte;

    cpu.set_sub(false);
    cpu.set_zero(cpu.a == 0);
    cpu.set_half_carry(false);
    cpu.set_carry(false);
}

fn rst_28h(cpu: &mut Cpu) {
    rst(cpu, 0x0028);
}

fn ld_a_mff00u8(cpu: &mut Cpu) {
    let byte = cpu.read_u8();
    cpu.a = cpu.mmu.read(0xff00 + byte as u16);
}

fn pop_af(cpu: &mut Cpu) {
    let word = cpu.pop_word();
    cpu.set_af(word);
}

fn di(cpu: &mut Cpu) {
    cpu.disable_int();
}

fn push_af(cpu: &mut Cpu) {
    cpu.push_word(cpu.af());
}

fn rst_30h(cpu: &mut Cpu) {
    rst(cpu, 0x0030);
}

fn ld_sp_hl(cpu: &mut Cpu) {
    cpu.sp = cpu.hl();
}

fn ld_a_mu16(cpu: &mut Cpu) {
    let word = cpu.read_u16();
    let byte = cpu.mmu.read(word);
    cpu.a = byte;
}

fn ei(cpu: &mut Cpu) {
    cpu.enable_int();
}

fn cp_a_u8(cpu: &mut Cpu) {
    let byte = cpu.read_u8();
    sub_set_flags(cpu, cpu.a, byte);
}

fn rst_38h(cpu: &mut Cpu) {
    rst(cpu, 0x0038);
}

fn rl_c(cpu: &mut Cpu) {
    cpu.c = rl(cpu, cpu.c);
}

fn rr_c(cpu: &mut Cpu) {
    cpu.c = rr(cpu, cpu.c);
}

fn rr_d(cpu: &mut Cpu) {
    cpu.d = rr(cpu, cpu.d);
}

fn rr_e(cpu: &mut Cpu) {
    cpu.e = rr(cpu, cpu.e);
}

fn sla_b(cpu: &mut Cpu) {
    cpu.b = sla(cpu, cpu.b);
}

fn swap_a(cpu: &mut Cpu) {
    cpu.a = swap(cpu, cpu.a)
}

fn srl_b(cpu: &mut Cpu) {
    cpu.b = srl(cpu, cpu.b);
}

fn bit_0_d(cpu: &mut Cpu) {
    bit_d(cpu, 0);
}

fn bit_7_h(cpu: &mut Cpu) {
    bit_h(cpu, 7);
}

fn res_0_a(cpu: &mut Cpu) {
    cpu.a = res(cpu.a, 0);
}

fn res_7_mhl(cpu: &mut Cpu) {
    let hl = cpu.hl();
    let byte = cpu.mmu.read(hl);
    let value = res(byte, 7);
    cpu.mmu.write(hl, value);
}

fn set_4_a(cpu: &mut Cpu) {
    cpu.a = set(cpu.a, 4);
}

/// 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
}

/// 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
}

/// 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_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_h(cpu: &mut Cpu, bit: u8) {
    cpu.set_sub(false);
    cpu.set_zero(bit_zero(cpu.h, 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 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 != 0);

    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;
}