VMS Help DCX Routines, DCX$ANALYZE_DATA  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    The DCX$ANALYZE_DATA routine performs statistical analysis
    on a data record. The results of the analysis are accumulated
    internally in the context area and are used by the DCX$MAKE_MAP
    routine to compute the mapping function.

    Format

      DCX$ANALYZE_DATA  context ,record

1 - Returns

    OpenVMS usage:cond_value
    type:         longword (unsigned)
    access:       write only
    mechanism:    by value

    Longword condition value. Most utility routines return a
    condition value in R0. Condition values that this routine can
    return are listed under Condition Values Returned.

2 - Arguments

 context

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

 record

    OpenVMS usage:char_string
    type:         character string
    access:       read only
    mechanism:    by descriptor
    Record to be analyzed. DCX$ANALYZE_DATA reads the record
    argument, which is the address of a descriptor for the record
    string. The maximum length of the record string is 65,535
    characters.

3 - Description

    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.

4 - Condition Values Returned

    DCX$_INVCTX        Error. The context variable is invalid, or the
                       context area is invalid or corrupted. This may
                       be caused by a failure to call the appropriate
                       routine to initialize the context variable or
                       by an application program error.
    DCX$_NORMAL        Normal successful completion.

    This routine also returns any condition values returned by
    LIB$ANALYZE_SDESC_R2.