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80386 Programmer's Reference Manual -- Opcode AAS |
AAS -- ASCII Adjust AL after Subtraction
OperationIF (AL AND 0FH) > 9 OR AF = 1 THEN AL := AL - 6; AL := AL AND 0FH; AH := AH - 1; AF := 1; CF := 1; ELSE CF := 0; AF := 0; FI; DescriptionExecute AAS only after a SUB instruction that leaves the byte result in the AL register. The lower nibbles of the operands of the SUB instruction must have been in the range 0 through 9 (BCD digits). In this case, AAS adjusts AL so it contains the correct decimal digit result. If the subtraction produced a decimal carry, the AH register is decremented, and the carry and auxiliary carry flags are set to 1. If no decimal carry occurred, the carry and auxiliary carry 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 AAS with OR AL, 30H.Flags AffectedAF and CF as described above; OF, SF, ZF, and PF are undefinedProtected Mode ExceptionsNoneReal Address Mode ExceptionsNoneVirtual 8086 Mode ExceptionsNone
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