Compression

Compression and levels

Methods

All implemented in Pascal, with no external compression libraries:

storing, lzma, ppmd, grzip, dict, rep, delta, tor (Tornado), lzp, mm, tta, 4x4, exe (x86 BCJ), lz4, dispack070 (DisPack), srep (SREP) and cm (context mixing), alone or chained.

parc a x.parc data -mlzma
parc a x.parc data -m"srep+lzma:64mb:max"
parc a x.parc data -m"exe+dispack070+lzma"

Levels

• -m0: store.
• -m1…-m9: FreeArc-style presets, tuned in PArc for better ratio and speed than FreeArc 0.67.1 (see Benchmarks).
• -mx: maximum ratio with fast decompression; uses PPMd for text and LZMA for binaries. Slightly smaller than -m9 and fast to extract.
• -mxx: absolute maximum ratio; uses the context-mixing codec (cm) on text and binaries. 8–16% smaller than -mx, but decompression is 5–40× slower.
• Default: -m4.

GRZip adapts its LZP parameters per block: BWT blocks of 4 MB or more use l64/h22, while small blocks keep the fast defaults. This is stored in the block mode, so existing archives remain readable.

Presets choose a method per file type (text, binary, already compressed, WAV/BMP, etc.) and group files into solid blocks. Without -s, PArc uses automatic 64 MB blocks for -m1…-m3 and 32 MB for -m4…-m9/-mx; -mxx keeps one block for maximum CM ratio. You can control blocking with -s- (non-solid), -se (by extension), -s<N>f (N files) or -s<N>m (minimum size). Independent data blocks are compressed in parallel (workers limited by PARC_THREADS). Extraction also decodes independent blocks in parallel before writing.

What to expect

• -m1…-m3: fast, good for interactive use.
• -m4/-m5: balance.
• -m6…-mx: large text/binary sets; more memory and time. -mxx only when decompression time does not matter.

Local results and methodology are in Benchmarks. FreeArc external compressors (precomp, ECM, JPG, PPMonstr, Durilca, CCM, etc.) are out of scope.