feat: comply with the fourth individual blargg test rom
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067ed03de3
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0eb40a8109
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@ -633,18 +633,17 @@ impl Instruction {
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use InstrRegister::*;
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let mut flags: Flags = *cpu.flags();
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let a_value = cpu.register(Register::A);
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let left = cpu.register(Register::A);
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let (cycles, sum) = match reg {
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B | C | D | E | H | L | A => {
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let value = cpu.register(reg.to_register()) + (flags.c() as u8);
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let sum = Self::add_u8s(a_value, value, &mut flags);
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let right = cpu.register(reg.to_register());
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let sum = Self::add_with_carry(left, right, flags.c(), &mut flags);
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(Cycle::new(4), sum)
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}
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IndirectHL => {
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let value = cpu.read_byte(cpu.register_pair(RegisterPair::HL))
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+ (flags.c() as u8);
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let sum = Self::add_u8s(a_value, value, &mut flags);
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let right = cpu.read_byte(cpu.register_pair(RegisterPair::HL));
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let sum = Self::add_with_carry(left, right, flags.c(), &mut flags);
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(Cycle::new(8), sum)
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}
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};
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@ -656,8 +655,9 @@ impl Instruction {
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MATHTarget::ImmediateByte(n) => {
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// ADC A, n | Add immediate byte plus the carry flag to A
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let mut flags: Flags = *cpu.flags();
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let value = n + (flags.c() as u8);
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let sum = Self::add_u8s(cpu.register(Register::A), value, &mut flags);
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let value = cpu.register(Register::A);
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let sum = Self::add_with_carry(value, n, flags.c(), &mut flags);
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cpu.set_flags(flags);
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cpu.set_register(Register::A, sum);
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@ -704,22 +704,21 @@ impl Instruction {
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Instruction::SBC(target) => match target {
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MATHTarget::Register(reg) => {
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// SBC A, r[z] | Subtract the value from register r[z] from A, add the Carry flag and then store in A
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// FIXME: See ADC, is this a correct understanding of this Instruction
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use InstrRegister::*;
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let mut flags: Flags = *cpu.flags();
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let a_value = cpu.register(Register::A);
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let left = cpu.register(Register::A);
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let (cycles, diff) = match reg {
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B | C | D | E | H | L | A => {
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let value = cpu.register(reg.to_register()) + (flags.c() as u8);
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let diff = Self::sub_u8s(a_value, value, &mut flags);
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let right = cpu.register(reg.to_register());
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let diff = Self::sub_with_carry(left, right, flags.c(), &mut flags);
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(Cycle::new(4), diff)
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}
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IndirectHL => {
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let value = cpu.read_byte(cpu.register_pair(RegisterPair::HL))
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+ (flags.c() as u8);
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let diff = Self::sub_u8s(a_value, value, &mut flags);
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let right = cpu.read_byte(cpu.register_pair(RegisterPair::HL));
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let diff = Self::sub_with_carry(left, right, flags.c(), &mut flags);
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(Cycle::new(8), diff)
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}
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};
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@ -730,10 +729,10 @@ impl Instruction {
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}
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MATHTarget::ImmediateByte(n) => {
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// SBC A, n | Subtract the value from immediate byte from A, add the carry flag and then store in A
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// FIXME: The Fixme above applies to this variant as well
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let mut flags: Flags = *cpu.flags();
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let value = n + (flags.c() as u8);
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let diff = Self::sub_u8s(cpu.register(Register::A), value, &mut flags);
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let value = cpu.register(Register::A);
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let diff = Self::sub_with_carry(value, n, flags.c(), &mut flags);
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cpu.set_flags(flags);
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cpu.set_register(Register::A, diff);
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@ -1494,6 +1493,26 @@ impl Instruction {
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diff
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}
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fn sub_with_carry(left: u8, right: u8, carry: bool, flags: &mut Flags) -> u8 {
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let carry = carry as u8;
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let (diff, did_overflow) = {
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let (tmp_diff, did) = left.overflowing_sub(right);
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let (diff, overflow) = tmp_diff.overflowing_sub(carry);
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(diff, did || overflow)
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};
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flags.update(
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diff == 0,
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true,
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(left & 0x0F).wrapping_sub(right & 0x0F).wrapping_sub(carry) > 0x0F,
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did_overflow,
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);
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diff
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}
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fn add_u16_i8_no_flags(left: u16, right: i8) -> u16 {
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if right < 0 {
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left.wrapping_sub((!right + 1) as u16)
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@ -1529,6 +1548,27 @@ impl Instruction {
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Self::bit_3_overflow(left, right),
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did_overflow,
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);
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sum
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}
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fn add_with_carry(left: u8, right: u8, carry: bool, flags: &mut Flags) -> u8 {
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let carry = carry as u8;
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let (sum, did_overflow) = {
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let (tmp_sum, did) = left.overflowing_add(right);
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let (sum, overflow) = tmp_sum.overflowing_add(carry);
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(sum, did || overflow)
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};
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flags.update(
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sum == 0,
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false,
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(((left & 0x0F) + (right & 0x0F) + carry) & 0x10) == 0x10,
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did_overflow,
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);
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sum
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}
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