DAA (Intel x86/64 assembly instruction)

모두의 코드
DAA (Intel x86/64 assembly instruction)

작성일 : 2020-09-01 이 글은 1254 번 읽혔습니다.

DAA

Decimal Adjust AL after Addition

참고 사항

아래 표를 해석하는 방법은 x86-64 명령어 레퍼런스 읽는 법 글을 참조하시기 바랍니다.

Opcode	Instruction	Op/ En	64-Bit Mode	Compat/ Leg Mode	Description
27	DAA	NP	Invalid	Valid	Decimal adjust AL after addition.

Instruction Operand Encoding

Op/En	Operand 1	Operand 2	Operand 3	Operand 4
NP	NA	NA	NA	NA

Description

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.

Operation

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;

Example

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

Flags Affected

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.

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

#UD

If in 64-bit mode.

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모두의 코드 DAA (Intel x86/64 assembly instruction)

DAA