IPP LZSS stream format/description

[Maier__Adrian_Nicuso]

Hello everyone,

I'm looking for Intel's IPP LZSS description. What I've found so far is that it uses 32KB window and MAX_MATCH=256 (Why?)

The most well-known LZSS implementation is Haruhiko Okumura's "LZSS.C". Even Microsoft Compress is based on his code - it's 4KB window, MAX_MATCH=17 (or 18 in some siblings)

Any ideas?

[Sergey_K_Intel]

Hi Ilya,

It is a specific of implementation. Now it's hard to recall why it was done so. Probably, because longer lengthes provide better compression ratio on standard data sets.

Regards,
Sergey

[Maier__Adrian_Nicuso]

It's understood. But original LZSS is byte-aligned - 8 literal/match flags are packet into one byte, 16-bit LZ token consists of 4-bit match length + 12-bit offset/match distance. Is Intel's LZSS byte-aligned as well? How exactly literals and matches are coded? Is this LZSS totally undocumented??

[Sergey_K_Intel]

IPP LZSS is totally undocumented, since we haven't assumed decoding of IPP LZSS-coded sequences with something else than IPP decoder. As far as I see from source code, the format is compatible with other LZSS implementations. That is, 1-bit flag, then either byte literal or offset-length pair (15-bit offset and 8-bit length).

The LZSS functions are oriented on source byte stream, so the LZSS encoder output is not byte-aligned (i.e. bit-oriented). Each EncodeLZSS function produces as much output as necessary dependending on input stream data and destination buffer length. The byte alignment happens only when EncodeLZSSFlush function is called.

Regards,
Sergey