3 replies to this topic

[fondi]

1).What do aaa and daa instructions in 8086 instruction set do? What are their applications on real world programming?
2).What are the applications of the PF (parity flag) in the 8086 status register? When do people use them?

Thanks :P

Edited by fondi, 25 September 2009 - 08:31 AM.

[kresh7]

AAA Stands for - (ASCII adjust AL after addition) it Changes contents of AL to valid unpacked decimal. The high order nibble is zeroed.

DAA Stands for - (Decimal adjust AL after addition) - Dunno xD

[dargueta]

The parity flag is useful for checking whether there's an odd or even number of bits set in the last arithmetic operation. As for DAA, I got this from Intel's instruction reference manual:

Quote

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.