OpenDocument Package : add LZMA compression algorithm

[Jérôme Bouat <jerome.bouat@wanadoo.fr>]

Hello,


The below document specifies that an OpenDocument Package is a zip file. Each file contained in the zip file "shall be non compressed (STORED) or compressed using the 'deflate' (DEFLATED) algorithm" :

http://docs.oasis-open.org/office/v1.2/os/OpenDocument-v1.2-os-part3.html#__RefHeading__752789_826425813

New versions of zip archive software support now the "LZMA" compression method in zip archives : 7-Zip since 2010, other free software (PeaZip, ...) and proprietary software.

The decompression speed of "LZMA" is quite the same than "deflate" but it offers a better compression ratio in most cases (especially with XML content) and seldom a worse compression ratio. During decompression, the used memory is lower than during compression.

The compression with "LZMA" is slower than with "deflate" and the required memory of the compression increases with the dictionary size. However the dictionary size still be small in many cases because the zip format compresses separately each member of the archive (one dictionary per member). Moreover, a computer has now many processing units (multi cores, ...) and thus enables parallel compression (for example : a compression process of one archive member per processing unit).

If you want to limit the required memory of compression/decompression, you can specify a maximum LZMA dictionary size.

Do you think this feature could be added to the next specification ?


Regards.