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fix(interpreter): always read word from memory

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It's not possible to know if a word or byte is requested, or rather
it would be a pain to retrieve that information.
It is much easier to just read a full word and then discard the top
half, if just a byte is needed.
This commit is contained in:
Marco Thomas
2025-06-17 12:00:56 +09:00
parent 200640447b
commit 7f4d79d840
2 changed files with 34 additions and 57 deletions
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53
src/interpreter/memory.rs
View File

@@ -48,18 +48,15 @@ impl Memory {
idx: MemoryIndex,
val: ImmediateOperand,
) {
match Memory::calc_memidx(regs, idx) {
ImmediateOperand::Byte(idx_byte) => match val {
ImmediateOperand::Byte(value) => {
log::debug!("Writing byte {value:#04x} to memory location {idx_byte:#04x}");
self.memory[idx_byte as usize] = value
let idx = Memory::calc_memidx(regs, idx);
match val {
ImmediateOperand::Byte(b) => {
log::debug!("Writing byte {b:#04x} to memory location {idx:#04x}");
self.memory[idx as usize] = b
}
ImmediateOperand::Word(_) => panic!("Cannot add Word to Byte Memory Index"),
},
ImmediateOperand::Word(idx_word) => match val {
ImmediateOperand::Word(value) => {
let byte1 = idx_word / 2;
let byte2 = idx_word / 2 + 1;
let byte1 = idx / 2;
let byte2 = idx / 2 + 1;
let [low, high]: [u8; 2] = value.to_le_bytes();
log::debug!(
"Writing bytes {low:#04x} and {high:#04x} to memory location {byte1:#04x} and {byte2:#04x}"
@@ -67,41 +64,21 @@ impl Memory {
self.memory[byte1 as usize] = low;
self.memory[byte1 as usize] = high;
}
ImmediateOperand::Byte(value) => {
self.memory[(idx_word * 2) as usize] = value;
}
},
}
}
/// Read into memory with a [`MemoryIndex`] as index.
pub fn read(
&self,
regs: &crate::interpreter::register::Register,
idx: MemoryIndex,
) -> ImmediateOperand {
match Memory::calc_memidx(regs, idx) {
ImmediateOperand::Byte(byte) => {
log::debug!("Reading byte {byte:#04x} from memory");
ImmediateOperand::Byte(self.memory[byte as usize])
}
ImmediateOperand::Word(word) => {
let byte1 = word / 2;
let byte2 = word / 2 + 1;
/// Always reads a whole word.
pub fn read(&self, regs: &crate::interpreter::register::Register, idx: MemoryIndex) -> Word {
let idx = Self::calc_memidx(regs, idx);
let byte1 = idx / 2;
let byte2 = idx / 2 + 1;
log::debug!("Reading bytes {byte1:#04x} and {byte2:#04x} from memory");
ImmediateOperand::Word(Word::from_le_bytes([
self.memory[byte1 as usize],
self.memory[byte2 as usize],
]))
}
}
Word::from_le_bytes([self.memory[byte1 as usize], self.memory[byte2 as usize]])
}
/// Calculate the absolute memory address from a [`MemoryIndex`] struct.
pub fn calc_memidx(
regs: &crate::interpreter::register::Register,
idx: MemoryIndex,
) -> ImmediateOperand {
pub fn calc_memidx(regs: &crate::interpreter::register::Register, idx: MemoryIndex) -> Word {
let mut base = ImmediateOperand::Word(0);
let mut index = ImmediateOperand::Word(0);
let mut disp = Displacement::IWord(0);
@@ -116,6 +93,6 @@ impl Memory {
disp = displacement;
}
base + index + disp
(base + index + disp).into()
}
}

18
src/interpreter/register.rs
View File

@@ -93,24 +93,24 @@ impl Register {
crate::register::Register::SP => self.sp = Word::from_le_bytes([0x0, byte]),
},
ImmediateOperand::Word(word) => {
let [low, high] = word.to_le_bytes();
match reg {
crate::register::Register::AX => self.ax.write(word),
crate::register::Register::BX => self.bx.write(word),
crate::register::Register::CX => self.cx.write(word),
crate::register::Register::DX => self.dx.write(word),
// crate::register::Register::AH => {}
// crate::register::Register::AL => {}
// crate::register::Register::BL => {}
// crate::register::Register::BH => {}
// crate::register::Register::CH => {}
// crate::register::Register::CL => {}
// crate::register::Register::DH => {}
// crate::register::Register::DL => {}
crate::register::Register::AH => self.ax.upper = high,
crate::register::Register::AL => self.ax.lower = low,
crate::register::Register::BH => self.ax.upper = high,
crate::register::Register::BL => self.ax.lower = low,
crate::register::Register::CH => self.ax.upper = high,
crate::register::Register::CL => self.ax.lower = low,
crate::register::Register::DH => self.ax.upper = high,
crate::register::Register::DL => self.ax.lower = low,
crate::register::Register::DI => self.di = word,
crate::register::Register::SI => self.si = word,
crate::register::Register::BP => self.bp = word,
crate::register::Register::SP => self.sp = word,
_ => panic!("Tried writing Word to Byte-sized register"),
}
}
}