position

    OpenVMS usage:longword_signed
    type:         longword integer (signed)
    access:       read only
    mechanism:    by reference

    Position (relative to the base address) of the first bit in
    the field that LIB$EXTV extracts. The position argument is the
    address of a signed longword integer containing the position.

 size

    OpenVMS usage:byte_unsigned
    type:         byte (unsigned)
    access:       read only
    mechanism:    by reference

    Size of the bit field LIB$EXTV extracts. The size argument is the
    address of an unsigned byte containing the size. The maximum size
    is 32 bits.

 base-address

    OpenVMS usage:longword_unsigned
    type:         longword (unsigned)
    access:       read only
    mechanism:    by value

    Base address of the bit field LIB$EXTV extracts from the
    specified variable bit field. The base-address argument is an
    unsigned longword containing the base address.