DEC             Decrement by 1                       Flags: O D I T S Z A P C
                                                            * - - - * * * * -
DEC destination

        Logic   destination ← destination - 1

    DEC subtracts one from the operand. Note that DEC does not change
    the carry flag.

    
    Opcode      Format
    48 + rw     DEC  r16
    48 + rd     DEC  r32
    FE /1       DEC  r/m8
    FF /1       DEC  r/m16
    FF /1       DEC  r/m32


    Length and timing
    Operands    Bytes   8088    186     286     386     486     Pentium
    r8           2       3       3       2       2       1       1   UV
    r16          1       3       3       2       2       1       1   UV
    r32          1       3       3       2       2       1       1   UV
    mem       2+d(0,2)  23+EA   15       7       6       3       3   UV