1 files changed, 146 insertions, 0 deletions
diff --git a/src/arm32/instruction_codec/decode_thumb.rs b/src/arm32/instruction_codec/decode_thumb.rs
new file mode 100644
index 0000000..fb1e8ee
--- /dev/null
+++ b/src/arm32/instruction_codec/decode_thumb.rs
@@ -0,0 +1,146 @@
+// 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::Result;
+use crate::arm32::{
+ Instruction,
+ InstructionCodec,
+ Predicate,
+ Register,
+ Sflag,
+ Shifter,
+ ThumbOpcode,
+};
+
+use core::num::Wrapping;
+
+impl InstructionCodec {
+ /// Decodes the given Thumb opcode.
+ ///
+ /// # Errors
+ ///
+ /// If the provided opcode is invalid (i.e. does not match any known pattern), an [InvalidOpcode](crate::Error::InvalidOpcode) error is returned.
+ pub fn decode_thumb(&mut self, opcode: ThumbOpcode) -> Result<Instruction> {
+ use Instruction::*;
+
+ let opcode = opcode.to_u16();
+
+ macro_rules! match_bits {
+ ($mask:expr) => {{
+ opcode & $mask == $mask
+ }};
+ }
+
+ let instruction = if match_bits!(0b11010000_00000000) {
+ let predicate = (opcode & 0b00001111_00000000).wrapping_shr(0x8) as u8;
+ let immediate = u32::from(opcode & 0b00000000_11111111);
+
+ if predicate == 0b1111 {
+ SoftwareInterrupt {
+ predicate: Predicate::Always,
+ immediate,
+ }
+ } else {
+ let predicate = Predicate::from_u8(predicate).unwrap();
+
+ let mut immediate = (immediate.wrapping_shl(0x18) as i32).wrapping_shl(0x17) as u32;
+ immediate = immediate.wrapping_add(self.address.0).wrapping_add(0x4);
+
+ Branch {
+ predicate,
+ immediate,
+ }
+ }
+ } else if match_bits!(0b00011000_00000000) {
+ let destination = Register::from_u8((opcode & 0b00000000_00000111) as u8).unwrap();
+ let base = Register::from_u8((opcode & 0b00000000_00111000).wrapping_shr(0x3) as u8).unwrap();
+
+ let subtract = opcode & 0b00000010_00000000 != 0x0;
+
+ let immediate_source = opcode & 0b00000100_00000000 != 0x0;
+ if immediate_source {
+ let source = u32::from((opcode & 0b00000001_11000000).wrapping_shr(0x6));
+
+ if subtract {
+ Subtract {
+ predicate: Predicate::Always,
+ destination,
+ base,
+ source: Shifter::Immediate(source),
+ s: Sflag::On,
+ }
+ } else {
+ Add {
+ predicate: Predicate::Always,
+ destination,
+ base,
+ source: Shifter::Immediate(source),
+ s: Sflag::On,
+ }
+ }
+ } else {
+ // register source
+
+ let source = Register::from_u8((opcode & 0b00000001_11000000).wrapping_shr(0x6) as u8).unwrap();
+
+ if subtract {
+ Subtract {
+ predicate: Predicate::Always,
+ destination,
+ base,
+ source: Shifter::from_register(source),
+ s: Sflag::On,
+ }
+ } else {
+ Add {
+ predicate: Predicate::Always,
+ destination,
+ base,
+ source: Shifter::from_register(source),
+ s: Sflag::On,
+ }
+ }
+ }
+ } else if match_bits!(0b01000111_00000000) {
+ let source = Register::from_u8((opcode & 0b00000000_01111000).wrapping_shr(0x3) as u8).unwrap();
+ let l = opcode & 0b00000000_10000000 != 0x0;
+
+ if l {
+ BranchLinkExchange {
+ predicate: Predicate::Always,
+ source: Shifter::from_register(source),
+ }
+ } else {
+ BranchExchange {
+ predicate: Predicate::Always,
+ source,
+ }
+ }
+ } else {
+ let _code = (opcode & 0b00011000_00000000).wrapping_shr(0xB) as u8;
+
+ todo!();
+ };
+
+ self.address += Wrapping(ThumbOpcode::SIZE);
+ Ok(instruction)
+ }
+}