zxc 0.15.0

What's new in 0.15.0

Release Notes

v0.15.0 is an integrity release built on a format break, and a speed release on top of it.

Decompression gains up to 24 % at levels 3-5 and 9-14 % at level 7 over v0.14.x; compression gains up to 39 % at levels 3-7. Level 3 now decodes 2.03x faster than LZ4 on Apple M2 (1.75x in v0.14), at a smaller size.

Format v9 redoes every integrity field：checksums that leave no header bit unprotected, block checksums over the decoded bytes, an optional archive digest, a seek table that validates itself group by group. On top of it, ZXC archives become multi-frame: cat a.zxc b.zxc is a valid archive, and the seekable reader spans every frame.

> ⚠️ Breaking change (format and ABI). The container format is now v9, and dictionaries move to .zxd version 2. v0.15.0 cannot read v8 archives or version-1 dictionaries, and v0.14.x cannot read what v0.15.0 writes (ZXC_ERROR_BAD_VERSION). The soname moves to libzxc.so.5：seekable block counts are 64-bit (#438), so programs linked against libzxc.so.4 must be rebuilt.
>
> Migrating v8 -> v9 is the same one-time transcode as before:
>
> sh
> zxc-old -dc old.zxc | zxc-new -z -c > new.zxc
>
>
> A dictionary is migrated with its archives：retrain it with the new build, or convert it byte for byte to keep its dict_id. Full guide, including the CLI output changes and the new Windows archive layout: docs/MIGRATION.md.

ZXC format v9

The compressed data is unchanged：same blocks, same parser, same entropy coders. The break is in what protects them and in how a reader finds its way. (#452)

• Multiplicative header checksums (#432). The XOR/shift construction left part of the compressed size unprotected; the same 2 bytes now cover every header bit.
• Block checksums cover the decoded bytes, seeded by position (#434). A block moved or duplicated inside an archive no longer verifies. The whole-archive hash gives way to an optional 8-byte archive digest folded from the block checksums.
• A seek table that validates itself (#436, #438). Groups of one 64-bit anchor and 64 block sizes, checked one group at a time and loaded lazily, so opening a large archive reads only what a range needs. Block counts are 64-bit.
• HAS_SEEK_TABLE header flag (#448). The table is announced instead of probed for. …

Full release notes »