path: root/src/cpu/isa_cmp.rs

/*
	Copyright 2021-2023 Gabriel Jensen.

	This file is part of Luma.

	Luma is free software: you can redistribute it
	and/or modify it under the terms of the GNU
	Affero General Public License as published by
	the Free Software Foundation, either version 3
	of the License, or (at your option) any later
	version.

	Luma is distributed in the hope that it will be
	useful, but WITHOUT ANY WARRANTY; without even
	the implied warranty of MERCHANTABILITY or
	FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	Affero General Public License for more details.

	You should have received a copy of the GNU
	Affero General Public License along with Luma.
	If not, see <https://www.gnu.org/licenses/>.
*/

use crate::log;
use crate::cpu::{Cpu, take_state_mut};
use crate::shifter::Shifter;

impl Cpu {
	pub(super) fn isa_cmp(&mut self, rn: u8, shifter: Shifter) {
		log!("cmp r{rn}, {shifter}");

		take_state_mut!(state, self);

		let rn_value        = state.read_register(rn);
		let (subtrahend, _) = state.shifter_value(shifter);

		let (temporary, c) = rn_value.overflowing_sub(subtrahend);
		let (_, v)         = (rn_value as i32).overflowing_sub_unsigned(subtrahend);

		let mut cpsr = state.read_cpsr() & 0b00001111111111111111111111111111;
		cpsr |= (v as u32) << 0x1C;
		cpsr |= (!c as u32) << 0x1D;
		cpsr |= ((temporary == 0x0) as u32) << 0x1E;
		cpsr |= temporary & 0b10000000000000000000000000000000;
		state.write_cpsr(cpsr);
	}
}