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AAA -- ASCII Adjust after Addition

Opcode    Instruction    Clocks    Description

37        AAA            4         ASCII adjust AL after addition

Operation

IF ((AL AND 0FH) > 9) OR (AF = 1)
THEN
   AL := (AL + 6) AND 0FH;
   AH := AH + 1;
   AF := 1;
   CF := 1;
ELSE
   CF := 0;
   AF := 0;
FI;

Description

Execute AAA only following an ADD instruction that leaves a byte result in the AL register. The lower nibbles of the operands of the ADD instruction should be in the range 0 through 9 (BCD digits). In this case, AAA adjusts AL to contain the correct decimal digit result. If the addition produced a decimal carry, the AH register is incremented, and the carry and auxiliary carry flags are set to 1. If there was no decimal carry, the carry and auxiliary flags are set to 0 and AH is unchanged. In either case, AL is left with its top nibble set to 0. To convert AL to an ASCII result, follow the AAA instruction with OR AL, 30H.

Flags Affected

AF and CF as described above; OF, SF, ZF, and PF are undefined

Protected Mode Exceptions

None

Real Address Mode Exceptions

None

up: Chapter 17 -- 80386 Instruction Set
prev: 17.2 Instruction Format
next: AAD ASCII Adjust AX before Division