Intel Pentium Instruction Set Reference
AAA - ASCII Adjust for Addition
| Code |
Mnemonic |
Description |
| 37 |
AAA |
ASCII adjust AL after addition |
Description
Adjusts the sum of two unpacked BCD values to create an unpacked BCD result. The AL register is the implied source and destination operand for this instruction. The AAA instruction is only useful when it follows an ADD instruction that adds (binary addition) two unpacked BCD values and stores a byte result in the AL register. The AAA instruction then adjusts the contents of the AL register to contain the correct 1-digit unpacked BCD result.
If the addition produces a decimal carry, the AH register is incremented by 1, and the CF and AF flags are set. If there was no decimal carry, the CF and AF flags are cleared and the AH register is unchanged. In either case, bits 4 through 7 of the AL register are cleared to 0.
| Operands |
Bytes |
Clocks |
| |
1 |
3 |
NP |
Flags
| ID |
unaffected |
DF |
unaffected |
| VIP |
unaffected |
IF |
unaffected |
| VIF |
unaffected |
TF |
unaffected |
| AC |
unaffected |
SF |
undefined. |
| VM |
unaffected |
ZF |
undefined. |
| RF |
unaffected |
AF |
sets to 1 if there is a decimal borrow; otherwise, it's cleared to 0 |
| NT |
unaffected |
PF |
undefined. |
| IOPL |
unaffected |
CF |
sets to 1 if there is a decimal borrow; otherwise, it's cleared to 0. |
| OF |
undefined. |