feat(decode): implement RV64I arithmetic operation instructions

Author: EmbroiderSnow

sim/src/decode.c

@@ -109,6 +109,11 @@ void decode_exec(Decode *s){
     INSTPAT("0000000 ????? ????? 110 ????? 01100 11", or     , R, R(rd) = src1 | src2);
     INSTPAT("0000000 ????? ????? 111 ????? 01100 11", and    , R, R(rd) = src1 & src2);
     // ADDW, SUBW, SLLW, SRLW, SRAW
+    INSTPAT("0000000 ????? ????? 000 ????? 01110 11", addw   , R, R(rd) = SEXT((uint32_t)src1 + (uint32_t)src2, 32));
+    INSTPAT("0100000 ????? ????? 000 ????? 01110 11", subw   , R, R(rd) = SEXT((uint32_t)src1 - (uint32_t)src2, 32));
+    INSTPAT("0000000 ????? ????? 001 ????? 01110 11", sllw   , R, R(rd) = SEXT((uint32_t)src1 << (src2 & 0x1f), 32));
+    INSTPAT("0000000 ????? ????? 101 ????? 01110 11", srlw   , R, R(rd) = SEXT((uint32_t)src1 >> (src2 & 0x1f), 32));
+    INSTPAT("0100000 ????? ????? 101 ????? 01110 11", sraw   , R, R(rd) = SEXT((int32_t)src1 >> (src2 & 0x1f), 32));
     // FENCE, FENCE.I
     // ECALL
     INSTPAT("0000000 00001 00000 000 00000 11100 11", ebreak , N, HALT(s->pc, R(10))); // R(10) is $a0