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C-5
INSTRUCTION SET DESCRIPTIONS
AAS ASCII Adjust for Subtraction:
AAS
Corrects the result of a previous
subtraction of two valid unpacked
decimal operands (the destination
operand must have been specified as
register AL). Changes the content of
AL to a valid unpacked decimal
number; the high-order half-byte is
zeroed.
Instruction Operands:
none
if
((AL) and 0FH) > 9 or (AF) = 1
then
(AL) ← (AL) – 6
(AH) ← (AH) – 1
(AF) ← 1
(CF) ← (AF)
(AL) ← (AL) and 0FH
AF
CF
DF –
IF –
OF ?
PF ?
SF ?
TF –
ZF ?
ADC Add with Carry:
ADC
dest
,
src
Sums the operands, which may be
bytes or words, adds one if CF is set
and replaces the destination operand
with the result. Both operands may be
signed or unsigned binary numbers
(see AAA and DAA). Since ADC incor-
porates a carry from a previous
operation, it can be used to write
routines to add numbers longer than
16 bits.
Instruction Operands:
ADC reg, reg
ADC reg, mem
ADC mem, reg
ADC reg, immed
ADC mem, immed
ADC accum, immed
if
(CF) = 1
then
(dest) ← (dest) + (src) + 1
else
(dest) ← (dest) + (src)
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