|
| |
Repeat while Not Equal
|
86/88 |
Y |
186 |
Y |
286 |
Y |
386 |
Y |
486 |
Y |
REPNE string_instruction |
|
Ovfl |
N |
Dir |
N |
Int |
N |
Trap |
N |
Sign |
N |
Zero |
N |
Aux |
N |
Prty |
N |
Carry |
N |
REPNE is a prefix that may be specified before any string instruction
(CMPS, LODS, MOVS, SCAS, and STOS). REPNE causes the string
instruction following it to be repeated, as long as CX does not equal
0; CX is decremented after each execution of the string instruction.
(For CMPS and SCAS, REP will also terminate the loop if the Zero Flag
is set after the string instruction executes. Compare this to REP,
which will terminate if the Zero Flag is clear.)
Notes: If CX is initially 0, the REPeated instruction is
skipped entirely.
The test for CX equal to 0 is performed before the
instruction is executed. The test for the Zero Flag
set (done only for CMPS and SCAS) is performed after
the instruction is executed.
REPNE and REPNZ are synonyms for the same
instruction.
You do not need to initialize ZF before using
repeated string instructions.
A repeated instruction that is interrupted between
repeats will correctly resume processing upon return
from the interrupt. However, if other prefixes are
used on a single instruction (for example, segment
override or LOCK) in addition to the REP, all
prefixes except the one that immediately preceded
the string instruction will be lost. Therefore, if
you must use more than one prefix on a single
instruction, you should disable interrupts before
the instruction, and enable them afterwards. Note
that even this precaution will not prevent a non-
maskable interrupt, and that lengthy string
operations may cause large delays in interrupt
processing.
------------------------------------ Timing ----------------------------------
OpCode Instruction 386 286 86
F2 A6 REPNE CMPS m8, m8 5+9*N 5+9*N 9+22*N
F2 A7 REPNE CMPS m16, m16 5+9*N 5+9*N 9+22*N
F2 A7 REPNE CMPS m32, m32 5+9*N
F2 AE REPNE SCAS m8 5+8*N 5+8*N 9+15*N
F2 AF REPNE SCAS m16 5+8*N 5+8*N 9+15*N
F2 AF REPNE SCAS m32 5+8*N
------------------------------------ Logic -----------------------------------
while CX <> 0 ; for MOVS, LODS, STOS
execute string instruction
CX = CX - 1
while CX <> 0 ; for CMPS, SCAS
execute string instruction
CX = CX - 1
if ZF = 0 terminate
See Also REP MOVS STOS CMPS SCAS LODS CLD STD |