Tested custom trees with the custom master fix in place — the original
still hangs. The tree incompatibility is a separate issue from the
SuperMaster path hang (both are real problems, both are now understood).
Custom trees give ~40% better compression for text data (1066 vs 1688
bytes for textfile.txt) but are incompatible with nuke1's assumptions.
Default tree retained for backward compatibility.
Updated roadmap to separate the backward compat (done) from the tree
optimization (remaining).
Testing revealed that custom Huffman trees from our treegen cause the
original UC2 Pro to hang even for single-file archives. The original's
ASM decompressor kernel (nuke1) has undocumented assumptions about tree
shapes that our treegen doesn't match.
Default tree is the only working option for backward compatibility.
Multi-file extraction remains a separate open issue (hangs even with
default tree, while listing works).
Root cause: the original UC2 Pro expects csize=0 in the cdir COMPRESS
record (it ignores the field entirely). UC2 v3 was writing the actual
compressed size, which confused the original's archive reader.
Additional changes:
- Use default Huffman tree for all blocks (ensures tree encoding compat)
- Write method=compression_level in cdir COMPRESS (was hardcoded to 1)
- Add tests/scripts/bitdump.py for bit-level bitstream analysis
Single-file UC2 v3 archives are now fully readable by the original UC2
Pro (listing and extraction verified in DOSBox-X). Multi-file archives
still hang — the cdir bitstream decodes correctly in our Python analyzer
but fails in the original's ASM decompressor kernel. Investigation
continues; the bitdump.py tool enables targeted comparison.
Port the original TreeGen/RepairLengths/CodeGen algorithms faithfully
from TREEGEN.CPP for bitstream compatibility with the 1992 UC2 Pro:
- treegen() now accepts max_code_bits parameter (13 for main trees,
7 for tree-encoding meta-tree)
- Heap uses >= for child comparison (prefer right child on ties),
matching original Reheap()
- BuildCodeTree uses extract-one-then-combine pattern
- RepairLengths uses sorted linked lists with cascading space-fill
- Single/zero symbol cases assign length 1 to two symbols
- tree_enc RLE: trigger at run > 6 (not >= 6), max 20 per chunk,
single RepeatCode per run
- First block uses default tree (tree-changed=0) matching original
behavior for small blocks
Full backward compatibility with original UC2 Pro archives (Direction 2)
is maintained. Forward compatibility (UC2 v3 -> original, Direction 1)
remains in progress — the original still hangs, likely due to residual
bitstream-level differences in the ASM decompressor kernel.
Implement a compressor that produces bitstreams compatible with the
existing Bobrowski decompressor. The engine uses LZ77 sliding-window
match finding with hash chains, Huffman entropy coding, and delta-coded
tree serialization matching the original UC2 format exactly.
New files:
- lib/src/compress.c: LZ77+Huffman compressor (~950 lines)
- lib/src/uc2_internal.h: shared constants, types, checksums
- lib/src/uc2_tables.c: vval/ivval delta tables, default Huffman tree
- tests/src/test_roundtrip.c: compress→archive→decompress→verify tests
Key details:
- 4 compression levels (Fast/Normal/Tight/Ultra) with tunable search
- Lazy evaluation for better match selection at higher levels
- Delta-coded Huffman tree serialization with RLE
- Fletcher/XOR checksum computation
- Round-trip test covers 8 patterns × 4 levels (32 test cases)
Fixed 28 errors in the hand-computed ivval inverse delta table (rows
9-13) that caused the decompressor to reconstruct wrong Huffman trees
from compressor output.
Decompression MVP based on Jan Bobrowski's portable unuc2/libunuc2.
CMake build system targeting Linux (GCC/Clang) with MSVC fallback.
Includes original UC2 source by Nico de Vries and unuc2-0.6 for reference.
Eremey Valetov