|
| |
Scan String
|
86/88 |
Y |
186 |
Y |
286 |
Y |
386 |
Y |
486 |
Y |
SCAS/SCASB/SCASW/SCASD destination |
|
Ovfl |
Y |
Dir |
N |
Int |
N |
Trap |
N |
Sign |
Y |
Zero |
Y |
Aux |
Y |
Prty |
Y |
Carry |
Y |
This instruction compares the accumulator (AL or AX) to the byte or
word pointed to by ES:DI. SCAS sets the flags according to the results
of the comparison; the operands themselves are not altered. After the
comparison, DI is 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.
Notes: This instruction is always translated by the
assembler into either SCASB, Scan String Byte, or
SCASW, Scan String Word, depending upon whether
destination-string refers to a string of bytes or
words. In either case, however, you must explicitly
load the DI register with the offset of the string.
SCAS is useful for searching a block for a given
byte or word value. Use CMPS, Compare String, if you
wish to compare two strings (or blocks) in memory,
element by element.
------------------------------------ Timing ----------------------------------
OpCode Instruction 386 286 86
AE SCAS m8 7 7 15
AF SCAS m16 7 7 15
AF SCAS m32 7
AE SCASB 7 7 15
AF SCASW 7 7 15
AF SCASD 7
------------------------------------ Logic -----------------------------------
CMP accumulator, (ES:DI)
if DF = 0
DI = DI + n
else
DI = DI - n
See Also CMP CMPS LODS MOVS STOS REP REPE REPNE CLD STD Flags |