MASKFLAG         Optimized AND                                      Extension

    Optimized form of the AND instruction that clears bits with the
    shortest possible instruction. Use only if the resulting contents of
    the flags registers are unimportant.

    Example:    RECORD state  zone:4, r5:5, chg:1, ins:1=1, bak:1=0
                ;...
                maskflag eax,NOT MASK chg