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opcode: ST, STI, STR

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- reorganized stuff
- explicit wrap (no overflows)
This commit is contained in:
dogeystamp 2024-01-06 15:06:00 -05:00
parent 519fe5a536
commit f98719879a
Signed by: dogeystamp
GPG Key ID: 7225FE3592EFFA38
1 changed files with 59 additions and 8 deletions
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67
src/vm/instruction.rs
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@ -4,6 +4,10 @@
use crate::vm::VM;
////////////////
// Main part
////////////////
#[derive(Debug)]
enum OpCode {
// branch
@ -72,15 +76,15 @@ pub fn execute_instruction(vm: &mut VM, instr: u16) {
OpCode::BR => todo!("BR"),
OpCode::ADD => todo!("ADD"),
OpCode::LD => op_ld(vm, instr),
OpCode::ST => todo!("ST"),
OpCode::ST => op_st(vm, instr),
OpCode::JSR => op_jsr(vm, instr),
OpCode::AND => todo!("AND"),
OpCode::LDR => op_ldr(vm, instr),
OpCode::STR => todo!("STR"),
OpCode::STR => op_str(vm, instr),
OpCode::RTI => todo!("RTI"),
OpCode::NOT => todo!("NOT"),
OpCode::LDI => op_ldi(vm, instr),
OpCode::STI => todo!("STI"),
OpCode::STI => op_sti(vm, instr),
OpCode::JMP => todo!("JMP"),
OpCode::RES => todo!("RES"),
OpCode::LEA => op_lea(vm, instr),
@ -100,24 +104,30 @@ fn sign_extend(x: u16, bits: usize) -> u16 {
fn no_op(vm: &mut VM, instr: u16) {}
////////////////
// Load ops
////////////////
fn op_lea(vm: &mut VM, instr: u16) {
let dr = (instr >> 9) & 0b111;
let offset = sign_extend(instr & 0x1ff, 9);
vm.registers.set_reg_with_cond(dr, vm.registers.pc + offset);
vm.registers
.set_reg_with_cond(dr, vm.registers.pc.wrapping_add(offset));
}
fn op_ld(vm: &mut VM, instr: u16) {
let dr = (instr >> 9) & 0b111;
let offset = sign_extend(instr & 0x1ff, 9);
vm.registers.set_reg_with_cond(dr, vm.mem.get_mem(vm.registers.pc + offset));
vm.registers
.set_reg_with_cond(dr, vm.mem.get_mem(vm.registers.pc.wrapping_add(offset)));
}
fn op_ldi(vm: &mut VM, instr: u16) {
let dr = (instr >> 9) & 0b111;
let offset = sign_extend(instr & 0x1ff, 9);
let indirect = vm.mem.get_mem(vm.registers.pc + offset);
let indirect = vm.mem.get_mem(vm.registers.pc.wrapping_add(offset));
vm.registers.set_reg_with_cond(dr, vm.mem.get_mem(indirect));
}
@ -127,7 +137,7 @@ fn op_ldr(vm: &mut VM, instr: u16) {
let base_r = (instr >> 6) & 0b111;
let offset = sign_extend(instr & 0x3f, 6);
let addr = vm.registers.get_reg(base_r) + offset;
let addr = vm.registers.get_reg(base_r).wrapping_add(offset);
vm.registers.set_reg_with_cond(dr, vm.mem.get_mem(addr));
}
@ -140,10 +150,51 @@ fn op_jsr(vm: &mut VM, instr: u16) {
vm.registers.pc = vm.registers.get_reg(base_r);
} else {
let offset = sign_extend(instr & 0x7ff, 11);
vm.registers.pc += offset;
vm.registers.pc = vm.registers.pc.wrapping_add(offset);
}
}
////////////////
// Store ops
////////////////
fn op_st(vm: &mut VM, instr: u16) {
let sr = (instr >> 9) & 0b111;
let offset = sign_extend(instr & 0x1ff, 9);
vm.mem.set_mem(
vm.registers.pc.wrapping_add(offset),
vm.registers.get_reg(sr),
);
}
fn op_sti(vm: &mut VM, instr: u16) {
let sr = (instr >> 9) & 0b111;
let offset = sign_extend(instr & 0x1ff, 9);
let addr = vm.mem.get_mem(vm.registers.pc.wrapping_add(offset));
vm.mem.set_mem(addr, vm.registers.get_reg(sr));
}
fn op_str(vm: &mut VM, instr: u16) {
let sr = (instr >> 9) & 0b111;
let base_r = (instr >> 6) & 0b111;
let offset = sign_extend(instr & 0x3f, 6);
// NOTE:
// this is how rodrigo did it:
//
// let addr = (vm.registers.get_reg(base_r) as u32 + offset as u32) as u16;
//
// apparently narrowing casts automatically wrap integers
// this is more explicit
let addr = vm.registers.get_reg(base_r).wrapping_add(offset);
vm.mem.set_mem(addr, vm.registers.get_reg(sr));
}
////////////////
// Trap/trap routines
////////////////
fn op_trap(vm: &mut VM, instr: u16) {
// conform to spec
// (we don't actually need it in this implementation)