How sld (shift left word) & srw (shift right word) generally work in stl programming?

SLD ( shift Left double word ) shifts the whole content of Accumulator to left bit by bit and the vacant space are getting filled by zeros.

for eg: sld 3   // transfer the content of accumulator to left 3 times.

SRD ( shift Right double word ) shifts the whole content of Accumulator to Right bit by bit and the vacant space are getting filled by zeros.