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// Copyright 2024 Gabriel Bjørnager Jensen.
//
// This file is part of Pollex.
//
// Pollex is free software: you can redistribute it
// and/or modify it under the terms of the GNU Af-
// fero General Public License as published by the
// Free Software Foundation, either version 3 of
// the License, or (at your option) any later ver-
// sion.
//
// Pollex 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 Af-
// fero General Public License along with Pollex.
// If not, see <https://www.gnu.org/licenses/>.
use crate::{assert_or_err, Error, Result};
use crate::arm32::{
Instruction,
InstructionCodec,
Predicate,
Shifter,
ThumbOpcode,
};
impl InstructionCodec {
/// Encodes the given Thumb instruction.
///
/// # Errors
///
/// If the given instruction cannot be encoded for Thumb, an error is returned.
pub fn encode_thumb(&mut self, instruction: Instruction) -> Result<ThumbOpcode> {
use Instruction::*;
let mut opcode = 0b00000000_00000000_u16;
match instruction {
Move {
predicate,
destination,
source,
s,
} => {
assert_or_err!(predicate == Predicate::Always, Error::IllegalPredicate);
if s.is_on() {
if let Shifter::Immediate { source } = source {
assert_or_err!(destination.is_low(), Error::IllegalRegister);
assert_or_err!(source <= 0xFF, Error::IllegalRegister);
opcode |= 0b00100000_00000000;
opcode |= source as u16;
opcode |= (destination as u16) << 0x8;
} else if let Shifter::LogicalShiftLeftImmediate { source, shift: 0x0 } = source {
assert_or_err!(destination.is_low(), Error::IllegalRegister);
assert_or_err!(source.is_low(), Error::IllegalRegister);
opcode |= 0b00100000_00000000;
opcode |= destination as u16;
opcode |= (source as u16) << 0x3;
} else {
return Err(Error::IllegalInstruction);
}
} else if let Shifter::LogicalShiftLeftImmediate { source, shift: 0x0 } = source {
opcode |= 0b01000110_00000000;
let h0 = destination.is_high();
let h1 = source.is_high();
opcode |= destination as u16 & 0b00000000_00000111;
opcode |= (source as u16 & 0b00000000_00000111) << 0x3;
opcode |= u16::from(h0) << 0x6;
opcode |= u16::from(h1) << 0x7;
} else {
// TODO: Shifters &c.
todo!();
}
}
_ => return Err(Error::IllegalInstruction),
}
self.address += ThumbOpcode::SIZE;
Ok(opcode.into())
}
}
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