[huf] Add generic C versions of the fast decoding loops #3449
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Add generic C versions of the fast decoding loops to serve architectures that don't have an assembly implementation. Also allow selecting the C decoding loop over the assembly decoding loop through a zstd decompression parameter `ZSTD_d_disableHuffmanAssembly`. I benchmarked on my Intel i9-9900K and my Macbook Air with an M1 processor. The benchmark command forces zstd to compress without any matches, using only literals compression, and measures only Huffman decompression speed: ``` zstd -b1e1 --compress-literals --zstd=tlen=131072 silesia.tar ``` The new fast decoding loops outperform the previous implementation uniformly, but don't beat the x86-64 assembly. Additionally, the fast C decoding loops suffer from the same stability problems that we've seen in the past, where the assembly version doesn't. So even though clang gets close to assembly on x86-64, it still has stability issues. | Arch | Function | Compiler | Default (MB/s) | Assembly (MB/s) | Fast (MB/s) | |---------|----------------|--------------|----------------|-----------------|-------------| | x86-64 | decompress 4X1 | gcc-12.2.0 | 1029.6 | 1308.1 | 1208.1 | | x86-64 | decompress 4X1 | clang-14.0.6 | 1019.3 | 1305.6 | 1276.3 | | x86-64 | decompress 4X2 | gcc-12.2.0 | 1348.5 | 1657.0 | 1374.1 | | x86-64 | decompress 4X2 | clang-14.0.6 | 1027.6 | 1659.9 | 1468.1 | | aarch64 | decompress 4X1 | clang-12.0.5 | 1081.0 | N/A | 1234.9 | | aarch64 | decompress 4X2 | clang-12.0.5 | 1270.0 | N/A | 1516.6 |
Before calling a dictionary good, make sure that it can compress an input. If v0.7.3 rejects v0.7.3's dictionary, fall back to the v1.0 dictionary. This is not the job of the verison test to test it, because we cannot fix this code.
Cyan4973
approved these changes
Jan 25, 2023
This was referenced Jan 25, 2023
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Add generic C versions of the fast decoding loops to serve architectures that don't have an assembly implementation. Also allow selecting the C decoding loop over the assembly decoding loop through a zstd decompression parameter
ZSTD_d_disableHuffmanAssembly.I benchmarked on my Intel i9-9900K and my Macbook Air with an M1 processor. The benchmark command forces zstd to compress without any matches, using only literals compression, and measures only Huffman decompression speed:
The new fast decoding loops outperform the previous implementation uniformly, but don't beat the x86-64 assembly. Additionally, the fast C decoding loops suffer from the same stability problems that we've seen in the past, where the assembly version doesn't. So even though clang gets close to assembly on x86-64, it still has stability issues.