Question

How many bytes will the following instructions increment the EDI register?

CLD
MOVSW

Answer 1

CLD (Clear Direction Flag)

If CLD() executed before MOVSB/MOVSW/MOVSD instruction, the CPU decrements (1 byte for MOVSB/ 2byts for MOVSW/ 4 bytes for MOVSD) EDI registers after moving each string element.

If CLD()executed after MOVSB/MOVSW/MOVSD instruction, the CPU increments 1 byte for MOVSB/ 2byts for MOVSW/ 4 bytes for MOVSD) EDI registers after moving each string element.

MOVSW (Move string, words)

Takes word at [ESI] and stores it in [EDI] and then increment/ decrement ESI and EDI by 2 bytes.