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/*
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::luma::device::{Branch, Device};
impl Device {
pub fn branch(&mut self, kind: Branch) {
match kind {
Branch::Offset(offset, l) => {
if l { // Check the l flag.
// Store the address of the following instruction
// in r14 (lr).
let pc_offset: u32 = match self.thumb() {
false => 0x4,
true => 0x2,
};
self.registers[0xE] = self.registers[0xF] - pc_offset;
self.log("link", format!("r14 => r15-{pc_offset}={:#010X}", self.registers[0xE]));
}
// Add the offset to r15 (pc).
let (address, _) = self.registers[0xF].overflowing_add_signed(offset);
// Add extra offset to move to the new fetch
// instruction.
let pc_offset = match self.thumb() {
false => 0x8,
true => 0x4,
};
self.registers[0xF] = address + pc_offset;
self.log("branch", format!("r15 => r15{offset:+}+{pc_offset} ({:#010X})", self.registers[0xF]));
},
Branch::Register(register) => {
// Use the address stored in 'register' as the new
// value in r15 (pc).
let value = self.registers[register as usize];
let t = value & 0b00000000000000000000000000000001 != 0x0;
self.cpsr = self.cpsr & 0b11111111111111111111111111011111 | (t as u32) << 0x5;
self.exchange(t);
let address = value & 0b11111111111111111111111111111110;
// Add extra offset to move to the new fetch
// instruction.
let pc_offset: u32 = match t {
false => 0x8,
true => 0x4,
};
self.registers[0xF] = address + pc_offset;
self.log("branch", format!("r15 => r{register}{pc_offset:+} ({:#010X})", self.registers[0xF]));
},
}
}
}
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