DAA — Decimal Adjust AL After Addition

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 addi-tion) 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.

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 > 99H) or (old_CF = 1))
THEN
                AL ← AL + 60H;
                CF ← 1;
            ELSE
                CF ← 0;
        FI;
FI;

ADD
        AL, BL
                Before: AL=79H BL=35H EFLAGS(OSZAPC)=XXXXXX
                After: AL=AEH BL=35H EFLAGS(0SZAPC)=110000
DAA
                Before: AL=AEH BL=35H EFLAGS(OSZAPC)=110000
                After: AL=14H BL=35H EFLAGS(0SZAPC)=X00111
DAA
                Before: AL=2EH BL=35H EFLAGS(OSZAPC)=110000
                After: AL=34H BL=35H EFLAGS(0SZAPC)=X00101

The CF and AF flags are set if the adjustment of the value results in a decimal carry in either digit of the result (see the “Operation” section above). The SF, ZF, and PF flags are set according to the result. The OF flag is undefined.

#UD If the LOCK prefix is used.

#UD If the LOCK prefix is used.

#UD If the LOCK prefix is used.

#UD If the LOCK prefix is used.

#UD If in 64-bit mode.

Source: Intel® 64 and IA-32 Architectures Software Developer's Manual, Combined Volumes (Order Number 325462-091US, March 2026)
Generated: 7-6-2026