This article needs additional citations for verification. (December 2018) (Learn how and when to remove this template message)
This flag is used to determine the direction ('forward' or 'backward') in which several bytes of data will be copied from one place in the memory, to another. The direction is important mainly when the original data position in memory and the target data position overlap.
- If it is set to 0 (using the clear-direction-flag instruction
CLD) — it means that string is processed beginning from lowest to highest address; such instructions mode is called auto-incrementing mode. Both the source index and destination index (like
MOVS) will increase them;
- In case it is set to 1 (using the set-direction-flag instruction
STD) — the string is processed from highest to lowest address. This is called auto-decrementing mode.
of string processing
||clear direction flag||0||lowest-to-highest address||auto-incrementing|
||set direction flag||1||highest-to-lowest address||auto-decrementing|