Intel 253666-024US Manuel D’Utilisation
Vol. 2A 3-257
INSTRUCTION SET REFERENCE, A-M
DAA—Decimal Adjust AL after Addition
DAA—Decimal Adjust AL after Addition
Description
Adjusts the sum of two packed BCD values to create a packed BCD result. The AL
register is the implied source and destination operand. The DAA instruction is only
useful when it follows an ADD instruction that adds (binary addition) two 2-digit,
packed BCD values and stores a byte result in the AL register. The DAA instruction
then adjusts the contents of the AL register to contain the correct 2-digit, packed
BCD result. If a decimal carry is detected, the CF and AF flags are set accordingly.
This instruction executes as described above in compatibility mode and legacy mode.
It is not valid in 64-bit mode.
register is the implied source and destination operand. The DAA instruction is only
useful when it follows an ADD instruction that adds (binary addition) two 2-digit,
packed BCD values and stores a byte result in the AL register. The DAA instruction
then adjusts the contents of the AL register to contain the correct 2-digit, packed
BCD result. If a decimal carry is detected, the CF and AF flags are set accordingly.
This instruction executes as described above in compatibility mode and legacy mode.
It is not valid in 64-bit mode.
Operation
IF 64-Bit Mode
THEN
#UD;
ELSE
old_AL ← AL;
old_CF ← CF;
CF ← 0;
IF (((AL AND 0FH)
>
9) or AF
=
1)
THEN
AL ← AL
+
6;
CF ← old_CF or (Carry from AL ← AL
+
6);
AF ← 1;
ELSE
AF
← 0;
FI;
IF ((old_AL
IF ((old_AL
>
99H) or (old_CF
=
1))
THEN
AL ← AL
+
60H;
CF
← 1;
ELSE
CF ← 0;
FI;
FI;
Opcode
Instruction
64-Bit
Mode
Compat/
Leg Mode
Description
27
DAA
Invalid
Valid
Decimal adjust AL after addition.