dogeystamp/lc3-vm
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implement LEA

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This commit is contained in:
dogeystamp 2024-01-06 13:36:09 -05:00
parent aa413bcaf2
commit a76d194cc7
Signed by: dogeystamp
GPG Key ID: 7225FE3592EFFA38
2 changed files with 38 additions and 22 deletions
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56
src/vm/instruction.rs
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@ -65,29 +65,43 @@ fn get_opcode(instruction: u16) -> OpCode {
}
}
pub fn execute_instruction(vm: &mut VM) {
let instruction: u16 = vm.mem.get_mem(vm.registers.pc);
let opcode = get_opcode(instruction);
pub fn execute_instruction(vm: &mut VM, instr: u16) {
let opcode = get_opcode(instr);
match opcode {
OpCode::BR => no_op(vm),
OpCode::ADD => no_op(vm),
OpCode::LD => no_op(vm),
OpCode::ST => no_op(vm),
OpCode::JSR => no_op(vm),
OpCode::AND => no_op(vm),
OpCode::LDR => no_op(vm),
OpCode::STR => no_op(vm),
OpCode::RTI => no_op(vm),
OpCode::NOT => no_op(vm),
OpCode::LDI => no_op(vm),
OpCode::STI => no_op(vm),
OpCode::JMP => no_op(vm),
OpCode::RES => no_op(vm),
OpCode::LEA => no_op(vm),
OpCode::TRAP => no_op(vm),
OpCode::NOOP => no_op(vm),
OpCode::BR => no_op(vm, instr),
OpCode::ADD => no_op(vm, instr),
OpCode::LD => no_op(vm, instr),
OpCode::ST => no_op(vm, instr),
OpCode::JSR => no_op(vm, instr),
OpCode::AND => no_op(vm, instr),
OpCode::LDR => no_op(vm, instr),
OpCode::STR => no_op(vm, instr),
OpCode::RTI => no_op(vm, instr),
OpCode::NOT => no_op(vm, instr),
OpCode::LDI => no_op(vm, instr),
OpCode::STI => no_op(vm, instr),
OpCode::JMP => no_op(vm, instr),
OpCode::RES => no_op(vm, instr),
OpCode::LEA => op_lea(vm, instr),
OpCode::TRAP => no_op(vm, instr),
OpCode::NOOP => no_op(vm, instr),
}
}
fn no_op(vm: &mut VM) {}
/// Sign extend a value, given the amount of bits it currently has
fn sign_extend(x: u16, bits: usize) -> u16 {
if (x >> (bits - 1) & 1) == 1 {
x | (0xffff << bits)
} else {
x
}
}
fn no_op(vm: &mut VM, instr: u16) {}
fn op_lea(vm: &mut VM, instr: u16) {
let dr = (instr >> 8) & 0b111;
let offset = sign_extend(instr & 0xff, 9);
vm.registers.set_reg(dr, vm.registers.pc + offset);
}

4
src/vm/mod.rs
View File

@ -190,7 +190,7 @@ impl VM {
let mut running: bool = true;
while running {
instruction::execute_instruction(self);
let instr = self.mem.get_mem(self.registers.pc);
// disallow reading past memory bounds
if self.registers.pc as usize == MEM_SIZE - 1 {
@ -198,6 +198,8 @@ impl VM {
} else {
self.registers.pc += 1;
}
instruction::execute_instruction(self, instr);
}
}
}