riscv/insns/mulh.h

   1 if(xpr64)
   2 {
   3   int64_t a = RS1;
   4   int64_t b = RS2;
   5   RD = (int128_t(a) * int128_t(b)) >> 64;
   6 }
   7 else
   8   RD = sext32((sext32(RS1) * sext32(RS2)) >> 32);