image/svg+xmlDAA—Decimal Adjust AL after AdditionInstruction Operand EncodingDescriptionAdjusts 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.OperationIF 64-Bit ModeTHEN#UD;ELSEold_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;ExampleADD AL, BL Before: AL=79H BL=35H EFLAGS(OSZAPC)=XXXXXXAfter: AL=AEH BL=35H EFLAGS(0SZAPC)=110000DAABefore: AL=AEH BL=35H EFLAGS(OSZAPC)=110000After: AL=14H BL=35H EFLAGS(0SZAPC)=X00111DAABefore: AL=2EH BL=35H EFLAGS(OSZAPC)=110000After: AL=34H BL=35H EFLAGS(0SZAPC)=X00101OpcodeInstructionOp/ En64-Bit ModeCompat/Leg ModeDescription27DAAZOInvalidValidDecimal adjust AL after addition.Op/EnOperand 1Operand 2Operand 3Operand 4ZONANANANA

image/svg+xmlFlags AffectedThe 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.Protected Mode Exceptions#UD If the LOCK prefix is used.Real-Address Mode Exceptions#UD If the LOCK prefix is used.Virtual-8086 Mode Exceptions#UD If the LOCK prefix is used.Compatibility Mode Exceptions#UD If the LOCK prefix is used.64-Bit Mode Exceptions#UDIf in 64-bit mode.

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