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Compress a longstring with Deflate

Note: Many $functions have been deprecated in favor of Object Oriented methods. The OO equivalent for the $Deflate function is the Deflate function.

This function compresses a longstring using the "deflate" algorithm. The deflate algorithm is described completely in RFC 1951. It is very effective with HTML and XML data.

The $Deflate function accepts two arguments and returns a longstring result.


%lstrc = $Deflate(%lstr, option)

Syntax terms

%lstrc The returned longstring.
%lstr The longstring to be compressed; it is required.
option A string that describes the type of compression to perform on the longstring. This argument is optional; if it is not specified, DYNAMIC compression is used. Valid options and their meanings are:
FIXED Indicates that compression is done with fixed codes. The fixed code tables used for compression (defined as part of RFC 1951) are somewhat optimized for ASCII character data, but slightly decrease the amount of CPU required to perform compression. Also, since the codes are already defined as part of the specification, they are not included in the compressed data.
DYNAMIC Indicates that the compression code tables are generated based on the input data. Dynamic tables typically provide somewhat better compression on most types of data. There is a very slight CPU overhead in computing the frequencies of byte values in the input data. Also, since the code tables are dynamic, they are included as part of the compressed data. This will increase the size of the compressed longstring, but these tables are small, since they are also stored in a compressed form.

Usage notes

  • If an invalid option is passed, or compression is not enabled for the current run, the request is cancelled.
  • The NCMPBUF parameter must be set by User 0 before the $Deflate function can be used. If $Deflate is called with NCMPBUF = 0, the request is cancelled.
  • As with any compression scheme, it is possible that a particular string will become longer after compression. This would happen, for example, if a deflated string were passed to $Deflate.
  • Short strings (less than 128 bytes) will typically compress better with the FIXED option.


In the following example, %LSTRC is set to the compressed version of the given string:

%LSTRC = $Deflate('How much wood could a woodchuck chuck', 'FIXED')

Note: No other string or longstring functions can be usefully performed on the compressed string until it is decompressed with $Inflate.

Products authorizing $Deflate

Products authorizing $Deflate