The DCX$ANALYZE_DATA routine performs statistical analysis on
    a single data record. This routine is called once for each data
    record to be analyzed.

    During analysis, the DCX facility gathers information that
    DCX$MAKE_MAP uses to create the compression/expansion function
    for the file. After the data records have been analyzed, call
    the DCX$MAKE_MAP routine. Upon receiving the DCX$_AGAIN status
    code from DCX$MAKE_MAP, you must again analyze the same data
    records (in the same order) using DCX$ANALYZE_DATA and then call
    DCX$MAKE_MAP again. On the second iteration, DCX$MAKE_MAP returns
    the DCX$_NORMAL status code, and the data analysis is complete.