REPNE            Repeat While not Equal              Flags: not altered

REPNE  string-instruction

Logic:    while CX <> 0                    ;for MOVS, LODS or STOS
execute string instruction
CX   CX - 1
                                          
while CX <> 0                    ;for CMPS or SCAS
execute string instruction
CX   CX - 1
if ZF <> 0 terminate loop    ;This is only difference
;between REP and REPNE

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.)

                                                                          
Operands                  Clocks   Transfers  Bytes   Example
-                        2          -        1     REPNE SCASB
                                                                          

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.

                                 Example                                  

The following example will find the first byte equal to 'A' in the
100-byte buffer at STRING.

CLD                     ;Scan string in forward direction
MOV     AL,'A'          ;Scan for 'A'
LEA     DI, STRING      ;Address to start scanning at
MOV     CX,100          ;Scanning 100 bytes
REPNE   SCASB                   ;   ...and scan it
DEC     DI              ;Back up DI to point to the 'A'

Upon termination of the repeated SCASB instruction, CX will be equal
to zero if a byte value of 'A' was not found in STRING, and non-zero
if it was.

See also: REP
See also: MOVS
See also: STOS
See also: CMPS
See also: SCAS
See also: LODS
See also: CLD
See also: STD

REPNE Repeat While Not Equal