ddidderr/zstd-rs
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

[huf] Add generic C versions of the fast decoding loops

Browse Source 
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 |
This commit is contained in:
Nick Terrell
2023-01-25 13:47:51 -08:00
committed by Nick Terrell
parent f3255bfeff
commit 8957fef554
13 changed files with 448 additions and 91 deletions
Download Patch File Download Diff File Expand all files Collapse all files
tests/fuzzer.c
+11
View File
@@ -684,6 +684,17 @@ static int basicUnitTests(U32 const seed, double compressibility)
if (r != CNBuffSize) goto _output_error; }
DISPLAYLEVEL(3, "OK \n");
DISPLAYLEVEL(3, "test%3i : decompress %u bytes with Huffman assembly disabled : ", testNb++, (unsigned)CNBuffSize);
{
ZSTD_DCtx* dctx = ZSTD_createDCtx();
size_t r;
CHECK_Z(ZSTD_DCtx_setParameter(dctx, ZSTD_d_disableHuffmanAssembly, 1));
r = ZSTD_decompress(decodedBuffer, CNBuffSize, compressedBuffer, cSize);
if (r != CNBuffSize || memcmp(decodedBuffer, CNBuffer, CNBuffSize)) goto _output_error;
ZSTD_freeDCtx(dctx);
}
DISPLAYLEVEL(3, "OK \n");
DISPLAYLEVEL(3, "test%3i : check decompressed result : ", testNb++);
{ size_t u;
for (u=0; u<CNBuffSize; u++) {