context

    OpenVMS usage:context
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference
    Value identifying the data stream that DCX$COMPRESS_DATA
    compresses. The context argument is the address of a longword
    containing this value. DCX$COMPRESS_INIT initializes the value;
    you should not modify it. You can define multiple context
    arguments to identify multiple data streams that are processed
    simultaneously.

 in_rec

    OpenVMS usage:char_string
    type:         character string
    access:       read only
    mechanism:    by descriptor
    Data record to be compressed. The in_rec argument is the address
    of the descriptor of the data record string.

 out_rec

    OpenVMS usage:char_string
    type:         character string
    access:       write only
    mechanism:    by descriptor
    Data record that has been compressed. The out_rec argument is
    the address of the descriptor of the compressed record that
    DCX$COMPRESS_DATA returns.

 out_length

    OpenVMS usage:word_signed
    type:         word integer (signed)
    access:       write only
    mechanism:    by reference
    Length (in bytes) of the compressed data record. The out_length
    argument is the address of a word into which DCX$COMPRESS_DATA
    returns the length of the compressed data record.