The Find First Clear or Set Bit routines search the field
    specified by the start position, size, and base for the first
    clear or set bit. LIB$FFC and LIB$FFS make the VAX FFC and VAX
    FFS instructions available as callable routines.

    Format

      LIB$FFC  position ,size ,base ,find-position

      LIB$FFS  position ,size ,base ,find-position