Document revision date: 30 March 2001

## OpenVMS Utility Routines Manual

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## DCX$ANALYZE_DONE

> The DCX$ANALYZE_DONE routine deletes the context area and sets the context variable to zero, undoing the work of the DCX$ANALYZE_INIT routine.

> Call DCX$ANALYZE_DONE after data records have been analyzed and the DCX$MAKE_MAP routine has created the map.

### Format

> DCX$ANALYZE_DONE context

### RETURNS

> OpenVMS usage: | cond_value
> type: | longword
> 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.

### Argument

> #### context

> OpenVMS usage: | context
> type: | longword
> access: | modify
> mechanism: | by reference

> Value identifying the data stream that DCX$ANALYZE_DONE deletes. The context argument is the address of a longword containing this value. DCX$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.

### 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$FREE_VM.

## DCX$ANALYZE_INIT

> The DCX$ANALYZE_INIT routine initializes the context area for a statistical analysis of the data records to be compressed.

### Format

> DCX$ANALYZE_INIT context [,item_code ,item_value]

### 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.

### Arguments

> #### context

> OpenVMS usage: | context
> type: | longword (unsigned)
> access: | write only
> mechanism: | by reference

> Value identifying the data stream that DCX$ANALYZE_INIT initializes. The context argument is the address of a longword containing this value. DCX$ANALYZE_INIT writes this context into the context argument; you should not modify its value. You can define multiple context arguments to identify multiple data streams that are processed simultaneously.

> #### item_code

> OpenVMS usage: | longword_unsigned
> type: | longword (unsigned)
> access: | read only
> mechanism: | by reference

> Item code specifying information that you want DCX$ANALYZE_INIT to use in its analysis of data records and in its computation of the mapping function. DCX$ANALYZE_INIT reads this item_code argument, which is the address of the longword contained in the item code.

> For each item_code argument specified in the call, you must also specify a corresponding item_value argument. The item_value argument contains the interpretation of the item_code argument.

> The following symbolic names are the five legal values of the item_code argument:

> > DCX$C_BOUNDED
> > DCX$C_EST_BYTES
> > DCX$C_EST_RECORDS
> > DCX$C_LIST
> > DCX$C_ONE_PASS

> #### item_value

> OpenVMS usage: | longword_unsigned
> type: | longword (unsigned)
> access: | read only
> mechanism: | by reference

> Value of the corresponding item_code argument. DCX$ANALYZE_INIT reads the item_value argument, which is the address of a longword containing the item value.

> The item_code and item_value arguments always occur as a pair, and together they specify one piece of "advice" for the DCX routines to use in computing the map function. Note that, unless stated otherwise in the list of item codes and item values, no piece of "advice" is binding on DCX; that is, DCX is free to follow or not to follow the "advice."

> The following table shows, for each item_code argument, the possible values for the corresponding item_value argument:

> Item Code | Corresponding Item Value
> --- | ---
> DCX$C_BOUNDED | A Boolean variable. If bit <0> is true (equals 1), you are stating your intention to submit for analysis all data records that will be compressed; doing so often enables DCX to compute a better compression algorithm. If bit <0> is false (equals 0) or if the DCX$C_BOUNDED item code is not specified, DCX computes a compression algorithm without regard for whether all records to be compressed will also be submitted for analysis.
> DCX$C_EST_BYTES | A longword value containing your estimate of the total number of data bytes that will be submitted for compression. This estimate is useful in those cases where fewer than the total number of bytes are presented for analysis. If you do not specify the DCX$C_EST_BYTES item code, DCX submits for compression the same number of bytes that was presented for analysis. Note that you may specify DCX$C_EST_RECORDS or DCX$C_EST_BYTES, or both.
> DCX$C_EST_RECORDS | A longword value containing your estimate of the total number of data records that will be submitted for compression. This estimate is useful in those cases where fewer than the total number of records are presented for analysis. If you do not specify the DCX$C_EST_RECORDS item code, DCX submits for compression the same number of bytes that was presented for analysis.
> DCX$C_LIST | Address of an array of 2* n+1 longwords. The first longword in the array contains the value 2* n+1. The remaining longwords are paired; there are n pairs. The first member of the pair is an item code, and the second member of the pair is the address of its corresponding item value. The DCX$C_LIST item code allows you to construct an array of item-code and item-value pairs and then to pass the entire array to DCX$ANALYZE_INIT. This is useful when your language has difficulty interpreting variable-length argument lists. Note that the DCX$C_LIST item code may be specified, in a single call, alone or together with any of the other item-code and item-value pairs.
> DCX$C_ONE_PASS | A Boolean variable. If bit <0> is true (equals 1), you make a binding request that DCX make only one pass over the data to be analyzed. If bit <0> is false (equals 0) or if the DCX$C_ONE_PASS item code is not specified, DCX may make multiple passes over the data, as required. Typically, DCX makes one pass.

### Description

> The DCX$ANALYZE_INIT routine initializes the context area for a statistical analysis of the data records to be compressed. The first (and typically the only) argument passed to DCX$ANALYZE_INIT is an integer variable to contain the context value. The DCX facility assigns a value to the context variable and associates the value with the created work area. Each time you want a record analyzed in that area, specify the associated context variable. You can analyze two or more files at once by creating a different work area for each file, giving each area a different context variable, and analyzing the records of each file in the appropriate work area.

### Condition Values Returned

> DCX$_INVITEM | Error; invalid item code. The number of arguments specified in the call was incorrect (this number should be odd), or an unknown item code was specified.
> DCX$_NORMAL | Normal successful completion.

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

## DCX$COMPRESS_DATA

> The DCX$COMPRESS_DATA routine compresses a data record. Call this routine for each data record to be compressed.

### Format

> DCX$COMPRESS_DATA context ,in_rec ,out_rec [,out_length]

### 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.

### Arguments

> #### 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.

### Description

> The DCX$COMPRESS_DATA routine compresses a data record. Call this routine for each data record to be compressed. As you compress each record, write the compressed record to the file containing the compression/expansion map. For each record, write the length of the record and substring string containing the record to the same file. See the COMPRESS DATA section in Example 7-1.

### Condition Values Returned

> DCX$_INVCTX | Error. The context variable is invalid, or the context area is invalid or corrupted. This may be caused by a failure to call the appropriate routine to initialize the context variable or by an application program error.
> DCX$_INVDATA | Error. You specified the item value DCX$C_BOUNDED in the DCX$ANALYZE_INIT routine and attempted to compress a data record (using DCX$COMPRESS_DATA) that was not presented for analysis (using DCX$ANALYZE_DATA). Specifying the DCX$C_BOUNDED item value means that you must analyze all data records that are to be compressed.
> DCX$_INVMAP | Error; invalid map. The map argument was not specified correctly in the DCX$ANALYZE_INIT routine or the context area is invalid.
> DCX$_NORMAL | Normal successful completion.
> DCX$_TRUNC | Error. The compressed data record has been truncated because the out_rec descriptor did not specify enough memory to accommodate the record.

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

## DCX$COMPRESS_DONE

> The DCX$COMPRESS_DONE routine deletes the context area and sets the context variable to zero.

### Format

> DCX$COMPRESS_DONE context

### 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.

### Argument

> #### context

> OpenVMS usage: | context
> type: | longword (unsigned)
> access: | write only
> mechanism: | by reference

> Value identifying the data stream that DCX$COMPRESS_DONE deletes. The context argument is the address of a longword containing this value. DCX$COMPRESS_INIT writes the value into the context argument; you should not modify its value. You can define multiple context arguments to identify multiple data streams that are processed simultaneously.

### Description

> The DCX$COMPRESS_DONE routine deletes the context area and sets the context variable to zero, undoing the work of the DCX$COMPRESS_INIT routine. Call DCX$COMPRESS_DONE when all data records have been compressed (using DCX$COMPRESS_DATA). After calling DCX$COMPRESS_DONE, call LIB$FREE_VM to free the virtual memory that DCX$MAKE_MAP used for the compression/expansion function.

### 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$FREE_VM.

## DCX$COMPRESS_INIT

> The DCX$COMPRESS_INIT routine initializes the context area for the compression of data records.

### Format

> DCX$COMPRESS_INIT context ,map

### 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.

### Arguments

> #### context

> OpenVMS usage: | context
> type: | longword (unsigned)
> access: | write only
> mechanism: | by reference

> Value identifying the data stream that DCX$COMPRESS_INIT initializes. The context argument is the address of a longword containing this value. You should not modify the context value after DCX$COMPRESS_INIT initializes it. You can define multiple context arguments to identify multiple data streams that are processed simultaneously.

> #### map

> OpenVMS usage: | address
> type: | longword (unsigned)
> access: | read only
> mechanism: | by reference

> The function created by DCX$MAKE_MAP. The map argument is the address of the compression/expansion function's virtual address.

> The map argument must remain at this address until data compression is completed and the context is deleted by means of a call to DCX$COMPRESS_DONE.

### Description

> The DCX$COMPRESS_INIT routine initializes the context area for the compression of data records.

> Call the DCX$COMPRESS_INIT routine after calling the DCX$ANALYZE_DONE routine.

### Condition Values Returned

> DCX$_INVMAP | Error; invalid map. The map argument was not specified correctly, or the context area is invalid.
> DCX$_NORMAL | Normal successful completion.

This routine also returns any condition values returned by LIB$GET_VM and LIB$FREE_VM.

## DCX$EXPAND_DATA

> The DCX$EXPAND_DATA routine expands (or restores) a compressed data record to its original state.

### Format

> DCX$EXPAND_DATA context ,in_rec ,out_rec [,out_length]

### 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.

### Arguments

> #### context

> OpenVMS usage: | context
> type: | longword (unsigned)
> access: | read only
> mechanism: | by reference

> Value identifying the data stream that DCX$EXPAND_DATA expands. The context argument is the address of a longword containing this value. DCX$EXPAND_INIT initializes this 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 expanded. 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 expanded. The out_rec argument is the address of the descriptor of the expanded record returned by DCX$EXPAND_DATA.

> #### out_length

> OpenVMS usage: | word_signed
> type: | word integer (signed)
> access: | write only
> mechanism: | by reference

> Length (in bytes) of the expanded data record. The out_length argument is the address of a word into which DCX$EXPAND_DATA returns the length of the expanded data record.

### Description

> The DCX$EXPAND_DATA routine expands (or restores) a compressed data record to its original state. Call this routine for each data record to be expanded.

### Condition Values Returned

> DCX$_INVCTX | Error. The context variable is invalid, or the context area is invalid or corrupted. This may be caused by a failure to call the appropriate routine to initialize the context variable or by an application program error.
> DCX$_INVDATA | Error. A compressed data record is invalid (probably truncated) and therefore cannot be expanded.
> DCX$_INVMAP | Error; invalid map. The map argument was not specified correctly, or the context area is invalid.
> DCX$_NORMAL | Normal successful completion.
> DCX$_TRUNC | Warning. The expanded data record has been truncated because the out_rec descriptor did not specify enough memory to accommodate the record.

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

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