XADD            Exchange and Add                     Flags: O D I T S Z A P C
                                                            * - - - * * * * *
XADD destination,source                              CPU: 486+

        Logic   XCHG destination,source
                ADD  destination,source

    XADD loads destination into source, then adds destination and the
    original source, returning the sum in destination.

        Example:        mov   dl, 8
                        mov   al, 3
                        xadd  dl, al
                        ; dl = 11, al = 8


    Opcode      Format
    0F C0 /r    XADD r/m8,r8
    0F C1 /r    XADD r/m16,r16
    0F C1 /r    XADD r/m32,r32


    Length and timing
    Operands    Bytes   8088    186     286     386     486     Pentium
    reg, reg     3                                       3       3   NP
     mem, reg   3+d(0-2)                                 4       4   NP