Question

I have a binary chunk of data 512 bytes long, I was wondering what the most efficient way would be if I wanted to shift it once to the right.

My best guess right now (very new to assembly) would be that I would have to first check a chunk (probably int) to see what it would shift out, shift, then carry in whatever the previous int would have shifted out and proceed carrying this shift down the data. Is there an easier way? If I have to use this carry technique, what’s the largest chunk I can shift? DWord? QWord?

Answer 1

If you just want to shift once, use the rotate-through-carry instructions.

First, make sure the carry flag is zero. Then:

1. Pull 4 bytes into a register
2. RCR
3. Write back out
4. Repeat with the next 4 bytes