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uc2/docs/license-audit.md
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Eremey Valetov 3dcfb3c4c4 License audit: SPDX headers + per-file provenance (closes 7cbbf97) 
Add SPDX-License-Identifier to every source file in lib/ and cli/.
Files derived from Bobrowski's libunuc2 retain LGPL-3.0-only;
cli/src/main.c (derived from his GPL-licensed unuc2 tool) and all
new Phase 2-7 work by Valetov are GPL-3.0-or-later.  No silent
LGPL-to-GPL upgrade has been applied.

CREDITS.md now lists each Bobrowski-derived file specifically rather
than crediting libunuc2 as generic 'inspiration'.

docs/license-audit.md records the full per-file provenance table,
the LGPL-3.0 -> GPL-3.0 chain rationale (LGPL sec. 4 Combined Works
is the operative clause; LGPL sec. 3 single-direction upgrade is
documented but not exercised), and confirms that:
- the 2015 LGPL-3.0 release in original/UC2_source/ is preserved
  unchanged;
- the 2020-2021 LGPL/GPL releases in original/unuc2-0.6/ are preserved
  unchanged;
- lib/src/super.bin is bit-identical to upstream and to de Vries's
  1992 distribution data.
2026-05-03 12:20:19 -04:00

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UC2 License Audit

Status: 2026-05-03. Maintained by Eremey Valetov.

UC2 v3 builds on three layers of prior work, each released under its own free-software licence. This document records per-file provenance, the LGPL-3.0 -> GPL-3.0 transition rationale, and the SPDX identifiers applied across the source tree.

Layer 1: Nico de Vries (1992-1996), released 2015

Nico de Vries authored UltraCompressor II as proprietary DOS software between 1992 and 1996. Danny Bezemer obtained permission to release the source code publicly and did so in 2015 under the GNU Lesser General Public License v3 (LGPL-3.0).

The 2015 release is preserved in this repository under original/UC2_source/ byte-for-byte unchanged, including its license header (GNU LESSER GENERAL PUBLIC LICENSE V3.txt) and the original binaries (uc2pro.exe, uc237b.exe, ue.exe). No file in lib/ or cli/ is a verbatim copy of any file in that release. The 2015 source serves as the format specification: it is read for documentation purposes (the on-disk archive layout, the SuperMaster dictionary contents, the Huffman tree encoding) but its C code is not linked in.

Relicensing impact: none. Layer 1 is preserved under its original LGPL-3.0 licence; nothing is moved upward to GPL-3.0.

Layer 2: Jan Bobrowski (2020-2021), libunuc2 / unuc2

Jan Bobrowski wrote a clean-room portable decompressor for UC2 v3 archives between 2020 and 2021. He released two products:

  • libunuc2 (decompression library) under LGPL-3.0
  • unuc2 (CLI tool) under GPL-3.0-or-later

The upstream source is preserved in original/unuc2-0.6/. The following files in this repository derive from Bobrowski's work and retain his original licence:

Current file Upstream origin Licence
lib/src/decompress.c original/unuc2-0.6/libunuc2.c LGPL-3.0-only
lib/src/list.h original/unuc2-0.6/list.h (identical) LGPL-3.0-only
lib/src/super.bin original/unuc2-0.6/super.bin (identical) data (de Vries)
lib/include/uc2/libuc2.h original/unuc2-0.6/libunuc2.h LGPL-3.0-only
cli/src/main.c original/unuc2-0.6/unuc2.c GPL-3.0-or-later
cli/src/compat/compat_win32.c original/unuc2-0.6/compat/compat.c (Win32 portions) LGPL-3.0-only
cli/src/compat/compat_dos.c derived from compat/compat.c (DOS adaptation by Valetov) LGPL-3.0-only

Modifications by Valetov in 2026 are released under the same licence as the file's upstream origin (LGPL-3.0 stays LGPL-3.0; GPL-3.0 stays GPL-3.0). No unilateral upgrade from LGPL to GPL has been applied to Bobrowski's work.

lib/src/super.bin is the SuperMaster dictionary block from the 1992 distribution. It is data, not code: a fixed binary table used as a compression-context priming dictionary. It is bit-identical to the file in Bobrowski's release and to the data extracted from de Vries's 1992 binaries.

Layer 3: Eremey Valetov (2026), UC2 v3 revival

The following files are new work by Valetov, originally authored for the UC2 v3 revival project, released under GPL-3.0-or-later:

File Function
lib/src/compress.c LZ77+Huffman compressor (inverse of decompress.c)
lib/src/uc2_tables.c Huffman delta-coding lookup tables
lib/src/uc2_internal.h Shared compressor/decompressor types and constants
lib/src/uc2_cdc.c + .h Content-defined chunking (Gear hash)
lib/src/uc2_merkle.c + .h Merkle DAG of deduplicated blocks
lib/src/uc2_blockstore.c + .h Cross-archive content-addressable block store
lib/src/uc2_simhash.c + .h SimHash near-duplicate detection
lib/src/uc2_delta.c + .h Binary delta compression
lib/src/uc2_rans.c + .h rANS entropy coder (method 10)
lib/src/uc2_dict.c + .h Dictionary metadata for cross-archive sharing
lib/src/uc2_preprocess.c + .h BCJ / BWT / delta-filter preprocessing
lib/src/uc2_lz4.c + .h LZ4 ultra-fast compression
lib/src/uc2_blake3.c + .h BLAKE3 cryptographic hashing
lib/src/uc2_sha256.c + .h SHA-256 (FIPS 180-4)
lib/src/uc2_ots.c + .h OpenTimestamps proof parser, walker, trailer
cli/src/compat/getopt.c Minimal POSIX getopt for MSVC
cli/src/main.c (post-9525a81 additions) OTS attach/extract/info, archive creation, scanning, benchmark

The Phase 3-7 modules are independent implementations. They reference the UC2 v3 archive format (which is a bitstream layout, not a copyrighted work) and use BLAKE3, SHA-256, LZ4, rANS, etc. from public-domain or self-authored reference implementations. None of these modules link to or derive from Bobrowski's code beyond using shared header types declared in uc2_internal.h.

Relicensing rationale

The composite project links Bobrowski's LGPL-3.0 library (lib/) into a GPL-3.0-or-later executable (cli/). This combination is permitted by LGPL-3.0 sec. 4 (Combined Works): the LGPL library may be used in GPL-licensed work without requiring the library itself to be relicensed.

No code has been moved from LGPL-3.0 to GPL-3.0 in this project. LGPL §3 permits a one-way upgrade from LGPL to GPL but exercising it is unnecessary here: the LGPL files remain LGPL, the GPL files remain GPL, and the combined work is distributable under GPL-3.0-or-later (as recorded in the project root LICENSE file).

If a downstream user wishes to redistribute lib/ standalone under LGPL-3.0, the LGPL-3.0 files are individually identifiable via their SPDX-License-Identifier headers.

SPDX policy

All source files in lib/ and cli/ carry one of two SPDX identifiers near the top:

  • SPDX-License-Identifier: LGPL-3.0-only for files derived from Bobrowski's libunuc2 / compat code.
  • SPDX-License-Identifier: GPL-3.0-or-later for cli/src/main.c (matches Bobrowski's original GPL-3.0-or-later choice for the CLI tool) and for all Valetov-authored Phase 2 through Phase 7 work.

Original copyright lines authored by Bobrowski are preserved verbatim where present. Where Valetov has added substantial new content to a Bobrowski-originated file (notably cli/src/main.c and compat_dos.c), an additional Valetov copyright line has been added without removing the original.

The 2015 LGPL-3.0 release in original/UC2_source/ and the 2020-2021 release in original/unuc2-0.6/ are preserved unchanged and are not subject to this policy: they retain whatever licence headers their authors shipped them with.

Audit checklist

  • LGPL-3.0 release by Bezemer/de Vries preserved unchanged in original/UC2_source/
  • LGPL-3.0 / GPL-3.0 release by Bobrowski preserved unchanged in original/unuc2-0.6/
  • Per-file provenance table above
  • SPDX-License-Identifier on every source file in lib/ and cli/
  • CREDITS.md attributes Bobrowski specifically for libunuc2-derived files, not as generic "inspiration"
  • LICENSE-HISTORY summary published as this file (docs/license-audit.md)
  • No silent LGPL-to-GPL upgrade: every Bobrowski-origin file retains LGPL-3.0-only

References

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