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INSTRUCTION SET DESCRIPTIONS
C-38
RET Return:
RET
optional-pop-value
Transfers control from a procedure
back to the instruction following the
CALL that activated the procedure.
The assembler generates an intra-
segment RET if the programmer has
defined the procedure near, or an
intersegment RET if the procedure has
been defined as far. RET pops the
word at the top of the stack (pointed to
by register SP) into the instruction
pointer and increments SP by two. If
RET is intersegment, the word at the
new top of stack is popped into the CS
register, and SP is again incremented
by two. If an optional pop value has
been specified, RET adds that value to
SP.
Instruction Operands:
RET immed8
(IP) ← ((SP) = 1:(SP))
(SP) ← (SP) + 2
if
inter-segment
then
(CS) ← ((SP) + 1:(SP))
(SP) ← (SP) + 2
if
add immed8 to SP
then
(SP) ← (SP) + data
AF –
CF –
DF –
IF –
OF –
PF –
SF –
TF –
ZF –
ROL Rotate Left:
ROL
dest, count
Rotates the destination byte or word
left by the number of bits specified in
the count operand.
Instruction Operands:
ROL reg, n
ROL mem, n
ROL reg, CL
ROL mem CL
(temp) ← count
do while (temp) ≠ 0
(CF) ← high-order bit of (dest)
(dest) ← (dest) × 2 + (CF)
(temp) ← (temp) – 1
if
count = 1
then
if
high-order bit of (dest) ≠ (CF)
then
(OF) ← 1
else
(OF) ← 0
else
(OF) undefined
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