|
| |
Compare String
|
86/88 |
Y |
186 |
Y |
286 |
Y |
386 |
Y |
486 |
Y |
CMPS/CMPSB/CMPSW/CMPSD dest,source |
|
Ovfl |
Y |
Dir |
N |
Int |
N |
Trap |
N |
Sign |
Y |
Zero |
Y |
Aux |
Y |
Prty |
Y |
Carry |
Y |
This instruction compares two values by subtracting the byte or word
pointed to by ES:DI, from the byte or word pointed to by DS:SI, and
sets the flags according to the results of the comparison. The
operands themselves are not altered. After the comparison, SI and DI
are incremented (if the direction flag is cleared) or decremented (if
the direction flag is set), in preparation for comparing the next
element of the string.
The REP prefixes can be used to process entire data items.
Note: This instruction is always translated by the
assembler into either CMPSB, Compare String Byte, or
CMPSW, Compare String Word, depending upon whether
source refers to a string of bytes or words. In
either case, you must explicitly load the SI and DI
registers with the offset of the source and
destination strings.
------------------------------------ Timing ----------------------------------
OpCode Instruction 386 286 86
A6 CMPS m8, m8 10 8 22
A7 CMPS m16, m16 10 8 22
A7 CMPS m32, m32 10 8
A6 CMPSB 10 8 22
A7 CMPSW 10 8 22
A7 CMPSD 10 8
------------------------------------ Logic -----------------------------------
CMP [DS:SI], [ES:DI] ; sets flags only
if DF = 0
SI = SI + n
DI = DI + n
else
SI = SI - n
DI = DI - n
See Also CMP SCAS LODS MOVS STOS REP REPE REPNE CLD STD Flags |