Implement SUB

src/instructions.rs

@@ -16,6 +16,7 @@ pub(crate) fn find_and_exec(instr: Instruction, core: &mut Core) -> Option<Instr
         0b01100 => match (instr.funct7(), instr.funct3()) {
             // OP
             (0b0000000, 0b000) => Some(rvi::add(core, instr)),
+            (0b0100000, 0b000) => Some(rvi::sub(core, instr)),
             (0b0000000, 0b111) => Some(rvi::and(core, instr)),
             (0b0000000, 0b110) => Some(rvi::or(core, instr)),
             _ => None,

src/instructions/rvi.rs

@@ -21,6 +21,16 @@ pub fn add(core: &mut Core, instr: Instruction) -> InstructionResult {
     InstructionResult::Normal
 }
 
+pub fn sub(core: &mut Core, instr: Instruction) -> InstructionResult {
+    core.reg_write(
+        instr.rd(),
+        core.reg_read(instr.rs1())
+            .wrapping_sub(core.reg_read(instr.rs2())),
+    );
+    core.advance_pc();
+    InstructionResult::Normal
+}
+
 pub fn addi(core: &mut Core, instr: Instruction) -> InstructionResult {
     core.reg_write(
         instr.rd(),