1 files changed, 58 insertions, 0 deletions
diff --git a/src/cpu/isa_sbc.rs b/src/cpu/isa_sbc.rs
new file mode 100644
index 0000000..28a7c0d
--- /dev/null
+++ b/src/cpu/isa_sbc.rs
@@ -0,0 +1,58 @@
+/*
+	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_sbc(&mut self, rd: u8, rn: u8, shifter: Shifter, s: bool) {
+		log!("{} r{rd}, r{rn}, {shifter}", match s {
+			false => "sbc",
+			true  => "sbcs",
+		});
+
+		take_state_mut!(state, self);
+
+		let rn_value = state.read_register(rn);
+		let c        = (state.read_cpsr() & 0b00100000000000000000000000000000) >> 0x1D;
+
+		let (mut subtrahend, _) = state.shifter_value(shifter);
+		subtrahend              = subtrahend.wrapping_sub(c);
+
+		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);
+			});
+		}
+	}
+}