/*
	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::{alu_exit_exception, Cpu, take_state_mut};
use crate::shifter::Shifter;

impl Cpu {
	pub(super) fn isa_sub(&mut self, rd: u8, rn: u8, shifter: Shifter, s: bool) {
		log!("{} r{rd}, r{rn}, {shifter}", match s {
			false => "sub",
			true  => "subs",
		});

		take_state_mut!(state, self);

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

		let (result, c) = rn_value.overflowing_sub(subtrahend);
		let (_, v)      = (rn_value as i32).overflowing_sub_unsigned(subtrahend);
		state.write_register(rd, result);

		if s {
			alu_exit_exception!(self, state, rd, {
				let mut cpsr = state.read_cpsr() & 0b00001111111111111111111111111111;
				cpsr |= (v as u32) << 0x1C;
				cpsr |= (!c as u32) << 0x1D;
				cpsr |= ((result == 0x0) as u32) << 0x1E;
				cpsr |= result & 0b10000000000000000000000000000000;
				state.write_cpsr(cpsr);
			});
		}
	}
}