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INSTRUCTION SET DESCRIPTIONS
C-30
MOVS Move String:
MOVS
dest-string, src-string
Transfers a byte or a word from the
source string (addressed by SI) to the
destination string (addressed by DI)
and updates SI and DI to point to the
next string element. When used in
conjunction with REP, MOVS
performs a memory-to-memory block
transfer.
Instruction Operands:
MOVS dest-string, src-string
MOVS (repeat) dest-string, src-string
(dest-string) ← (src-string) AF –
CF –
DF –
IF –
OF –
PF –
SF –
TF –
ZF –
MUL Multiply:
MUL
src
Performs an unsigned multiplication of
the source operand and the accumu-
lator. If the source is a byte, then it is
multiplied by register AL, and the
double-length result is returned in AH
and AL. If the source operand is a
word, then it is multiplied by register
AX, and the double-length result is
returned in registers DX and AX. The
operands are treated as unsigned
binary numbers (see AAM). If the
upper half of the result (AH for byte
source, DX for word source) is non-
zero, CF and OF are set; otherwise
they are cleared.
Instruction Operands:
MUL reg
MUL mem
When Source Operand is a Byte:
(AX) ← (AL) × (src)
if
(AH) = 0
then
(CF) ← 0
else
(CF) ← 1
(OF) ← (CF)
When Source Operand is a Word:
(DX:AX) ← (AX) × (src)
if
(DX) = 0
then
(CF) ← 0
else
(CF) ← 1
(OF) ← (CF)
AF ?
CF
DF –
IF –
OF
PF ?
SF ?
TF –
ZF ?
Table C-4. Instruction Set (Continued)
Name Description Operation
Flags
Affected
NOTE: The three symbols used in the Flags Affected column are defined as follows:
– the contents of the flag remain unchanged after the instruction is executed
? the contents of the flag is undefined after the instruction is executed
the flag is updated after the instruction is executed