Wave 2: make default build MIT-clean (public-domain Blowfish, opt-in GPL for Kogado/WARC RNG)

[Alex123666tw]

Summary — Wave 2: make the default release binary truly MIT

Builds on #1. Removes GPL code from the default build so the released ArcFormats.dll is MIT-clean, while keeping the GPL-dependent format paths available behind an opt-in build flag.

Replaced GPLv2 Blowfish with a public-domain implementation

ArcFormats/Blowfish.cs was Novell's GPLv2 file. Rewrote it from the public-domain Blowfish reference (Schneier / Kocher), preserving the exact public API and per-path byte order.

Verified byte-identical to the old implementation:

• 34/34 standard ECB test vectors (cross-checked against an independent Blowfish implementation to rule out a bad vector table).
• Differential test of all three code paths — Decipher(byte[]), CreateDecryptor().TransformBlock, Decipher(ref,ref) — at 20,000 random cases each: 0 mismatches; round-trip 0 failures.

So the engines that use Blowfish (CatSystem2, TanukiSoft, Tamamo, Musica, Aims) are unaffected.

Excluded the remaining GPLv2 file from the default build

ArcFormats/KogadoCocotte.cs (GPLv2 — Schindler qsmodel range coder, ported by morkt) has no clean MIT replacement, so it is now compiled only when INCLUDE_GPL is defined. It provides CRangeCoder, used by two format paths, both gated behind #if INCLUDE_GPL (throwing a clear NotSupportedException otherwise):

• Kogado Cocotte compression (Hypatia ArcKogado, compression type 2)
• ShiinaRio WARC versions 120–169 RNG-compressed index (ArcWARC.UnpackRNG). WARC ≥170 uses ZLib and is unaffected.

Result: the default build produces an MIT-clean ArcFormats.dll — verified that KogadoCocotte.cs is not in the default compile set (MSBuild -getItem:Compile) and that no compiled source contains GPL text. Building with -p:DefineConstants="TRACE;INCLUDE_GPL" restores those two format paths (that binary is then GPLv2).

Docs

README.md / NOTICE updated (EN + 繁中): the default release is MIT-clean; the optional INCLUDE_GPL build adds one GPLv2 component (and which formats it enables). licenses/GPL-2.0.txt retained for that build.

Testing

• Default build (GameRes + ArcFormats + Console): 0 errors. INCLUDE_GPL build: 0 errors.
• SoftPal data.pac extraction regression: the 3 extracted files are SHA-256-identical to baseline (SoftPal uses none of the changed code; confirms the pipeline is intact).
• Blowfish differential + standard vectors as above.

Depends on #1 (based on its branch; will retarget to main once #1 merges).

🤖 Generated with Claude Code