Lb is a load byte, which only takes a byte of 4 4 bits, but it needs to be placed in a 32-bit register, so it needs to be completed in front. Sign bit padding means that the positive number is 0 and the negative number is 1. If111is actually-1, take it out and put it into a 32-bit register. If it is preceded by 1, the value is still-1. If it is 00 1, then add 0.