Add ZXC compression codec#120662
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Integrates the ZXC library as a new, optional compression format. This includes: - New build options to enable/disable ZXC and its built-in library. - Build system integration with CPU architecture-specific SIMD optimizations (SSE2, AVX2, AVX512, NEON) for core compression/decompression functions. - API exposure in `Compression` and `FileAccess` classes. - A new project setting for ZXC compression level. - Documentation updates and round-trip tests. - Inclusion of the `zxc` third-party library (BSD-3-clause) and its `rapidhash` dependency (Expat).
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What problem(s) does this PR solve?
Adds ZXC as a new optional compression format, alongside FastLZ, Deflate, Zstandard, gzip and Brotli. ZXC is an asymmetric LZ codec (BSD-3-Clause), optimized for very fast decompression. That fits the engine's "compress once, decompress many times at load" pattern. Full rationale is in the proposal.
Additional information
Compression::MODE_ZXCwith fullcompress/decompress/get_max_compressed_buffer_size.FileAccess.COMPRESSION_ZXC, works fromPackedByteArray.compress()/decompress()andFileAccess.open_compressed().compression/formats/zxc/compression_level(range 1-6, default 3).zxcandbuiltin_zxc, gated by theZXC_ENABLEDdefine.zxc=nobuilds cleanly.zxc_compress.c /zxc_decompress.c/zxc_huffman.care compiled once per ISA variant (sse2/avx2/avx512on x86_64,neonon ARM) and selected at runtime viaCPUID/getauxval. No-march=native, single portable binary.thirdparty/zxc/(v0.12.0), documented inthirdparty/README.mdandCOPYRIGHT.txt(BSD-3-Clause, plus vendoredrapidhashunder Expat/MIT).FileAccess.xml,ProjectSettings.xml) and round-trip unit tests.Benchmark
Standalone harness mirroring the exact Compression calls (zstd level 3, fastlz, zxc). Apple M3, clang -O3, single-threaded, zstd 1.5.7, zxc 0.12.0 (NEON path selected at runtime). Throughput in MB/s (decimal). Every row round-trips.
Structured text
doc/classes/*.xml(8.3 MB)Low-compressibility binary, editor-binary slice (25 MB)
The win is decode speed: zxc-3 is 2x faster than zstd-3 and 4x faster than fastlz. It's a strong FastLZ replacement: better ratio and decode speed. It does not beat Zstandard on ratio or compression speed. Useful range is L1-L5.
Real-world load (Godot engine path)
Loading a serialized
PackedScene(16k-node level, 1.71 MB) through the engine, optimized editor build (dev_build=no optimize=speed), Apple M3:open_compressed)ZXC decodes the scene 4.7x faster than zstd-3 in pure decode, 2.2x faster through the full FileAccessCompressed path. The trade-off: zstd's output is 2.2x smaller. So on slow / cold storage where I/O dominates, the smaller file narrows the gap. ZXC's advantage is largest when data is cached or storage is fast.