"IBM personal computer assembly language tutorial" - читать интересную книгу автора (Auerbach J.)

d. Flow of control instructions. These deserve study in themselves
and we will discuss them a little more. They include

1) CALL, RET -- call and return

2) INT, IRET -- interrupt and return-from-interrupt

3) JMP -- jump or "branch"

4) LOOP, LOOPNZ, LOOPZ -- special (and useful) instructions which
implement a counted loop similar to the 370 BCT instruction

5) various conditional jump instructions

e. String instructions. These implement a limited storage-to-storage
instruction subset and are quite powerful. All of them have the
property that

1) The source of data is described by the combination DS and SI.

2) The destination of data is described by the combination ES and
DI.

3) As part of the operation, the SI and/or DI register(s) is(are)
incremented or decremented so the operation can be repeated.



IBM PC Assembly Language Tutorial 8


They include

1) CMPSB/CMPSW -- compare byte or word

2) LODSB/LODSW -- load byte or word into AL or AX

3) STOSB/STOSW -- store byte or word from AL or AX

4) MOVSB/MOVSW -- move byte or word

5) SCASB/SCASW -- compare byte or word with contents of AL or AX

6) REP/REPE/REPNE -- a prefix which can be combined with any of
the above instructions to make them execute repeatedly across a
string of data whose length is held in CX.

f. Flag instructions: CLI, STI, CLD, STD, CLC, STC. These can set or
clear the interrupt (enabled) direction (for string operations) or