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16bit substraction is not really needed

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This commit is contained in:
Franco Colmenarez 2021-10-18 08:44:22 -05:00
parent 7c804029ad
commit 9adf41ee47
1 changed files with 21 additions and 53 deletions
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74
src/cpu.rs
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@ -563,59 +563,38 @@ impl CPU {
},
Opcode::SUB(params) => {
self.registers.increment(Register::PC, 1);
self.registers.set_flag(FlagRegister::Substract, true);
let mut register = Register::A;
let mut val1: u16 = 0;
let mut val2: u16 = 0;
match params {
OpcodeParameter::Register_Register(reg1, reg2) => {
register = reg1;
val1 = self.registers.get(reg1);
if reg1.is_8bit() && reg2.is_8bit() {
let carry = self.registers.get(reg2) > self.registers.get(reg1);
self.registers.set_flag(FlagRegister::Carry, carry);
self.registers.set_flag(FlagRegister::HalfCarry, sub_half_carry(self.registers.get_8bit(reg1), self.registers.get_8bit(reg2)));
let mut val1 = self.registers.get(reg1);
let val2 = self.registers.get(reg2);
if carry {
val1 = val1 | 0x100;
}
self.registers.set(reg1, val1 - val2);
} else if reg1.is_16bit() && reg2.is_16bit() {
let mut val1 = self.registers.get(reg1) as u32;
let val2 = self.registers.get(reg2) as u32;
let carry = val2 > val1;
if carry {
val1 = val1 | 0x10000;
}
let result = val1 - val2;
self.registers.set(reg1, join_bytes(result.to_be_bytes()[2], result.to_be_bytes()[3]));
self.registers.set_flag(FlagRegister::Carry, carry);
self.registers.set_flag(FlagRegister::HalfCarry, sub_half_carry(val1.to_be_bytes()[2], val2.to_be_bytes()[2]));
val2 = self.registers.get(reg2);
} else if reg1.is_8bit() && reg2.is_16bit() {
let mut val1 = self.registers.get(reg1) as u16;
let val2 = bus.read(self.registers.get(reg2)) as u16;
let carry = val2 > val1;
if carry {
val1 = val1 | 0x100;
}
self.registers.set(reg1, val1 - val2);
self.registers.set_flag(FlagRegister::HalfCarry, sub_half_carry(val1.to_be_bytes()[1], val2.to_be_bytes()[1]));
self.registers.set_flag(FlagRegister::Carry, carry);
val2 = bus.read(self.registers.get(reg2)) as u16;
}
self.registers.set_flag(FlagRegister::Zero, self.registers.get(reg1) == 0);
},
OpcodeParameter::Register_U8(reg1, val) => {
self.registers.increment(Register::PC, 1);
let mut val1 = self.registers.get(reg1) as u16;
let val2 = val as u16;
let carry = val2 > val1;
if carry {
val1 = val1 | 0x100;
}
let result = val1 - val2;
self.registers.set(reg1, join_bytes(result.to_be_bytes()[0], result.to_be_bytes()[1]));
self.registers.set_flag(FlagRegister::HalfCarry, sub_half_carry(val1.to_be_bytes()[1], val2.to_be_bytes()[1]));
self.registers.set_flag(FlagRegister::Zero, self.registers.get(reg1) == 0);
self.registers.set_flag(FlagRegister::Carry, carry);
register = reg1;
val1 = self.registers.get(reg1);
val2 = val as u16;
},
_ => {},
};
let carry = val2 > val1;
if carry {
val1 = val1 | 0x100;
}
let result = val1 - val2;
println!("{} {}", val1, val2);
self.registers.set(register, result);
self.registers.set_flag(FlagRegister::Zero, self.registers.get(register) == 0);
self.registers.set_flag(FlagRegister::Substract, true);
self.registers.set_flag(FlagRegister::Carry, carry);
self.registers.set_flag(FlagRegister::HalfCarry, sub_half_carry(val1.to_be_bytes()[1], val2.to_be_bytes()[1]));
},
// Increment by 1
Opcode::INC(affect_flags, register) => {
@ -2133,17 +2112,6 @@ mod tests {
assert_eq!(cpu.registers.get_flag(FlagRegister::Zero), true);
assert_eq!(cpu.registers.get(Register::B), 0);
assert_eq!(cpu.registers.get(Register::PC), 0x102);
let mut cpu = CPU::new();
cpu.registers.set(Register::BC, 0b0001000000000000);
cpu.registers.set(Register::HL, 0b0100100000000000);
cpu.exec(Opcode::SUB(OpcodeParameter::Register_Register(Register::BC, Register::HL)), &mut bus);
assert_eq!(cpu.registers.get_flag(FlagRegister::Substract), true);
assert_eq!(cpu.registers.get_flag(FlagRegister::Zero), false);
assert_eq!(cpu.registers.get_flag(FlagRegister::HalfCarry), true);
assert_eq!(cpu.registers.get_flag(FlagRegister::Carry), true);
assert_eq!(cpu.registers.get(Register::BC), 0b1100100000000000);
assert_eq!(cpu.registers.get(Register::PC), 0x101);
}
#[test]