Reduces memory when blocks are guaranteed to be smaller than allowed by
the format. This is useful for streaming compression in conjunction with
ZSTD_c_maxBlockSize.
This PR saves 2 * (formatMaxBlockSize - paramMaxBlockSize) when streaming.
Once it is rebased on top of PR #3616 it will save
3 * (formatMaxBlockSize - paramMaxBlockSize).
The split literals buffer patch increased streaming decompression memory
by 64KB (shrunk lit buffer from 128KB to 64KB, and added 128KB). This
patch removes the added 128KB buffer, because it isn't necessary.
The buffer was there because the literals compression code didn't know
the true `blockSizeMax` of the frame, and always put split literals so
they ended 128KB - 32 from the beginning of the block. Instead, we can
pass down the true `blockSizeMax` and ensure that the split literals
end up at `blockSizeMax - 32` from the beginning of the block. We
already reserve a full `blockSizeMax` bytes in streaming mode, so we
won't be overwriting the extDict window.
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 |
```
for f in $(find . \( -path ./.git -o -path ./tests/fuzz/corpora \) -prune -o -type f);
do
sed -i 's/Facebook, Inc\./Meta Platforms, Inc. and affiliates./' $f;
done
```
This saves some 1.7Kb in rodata section (x86_64, zstd tool),
while assembler code stays the same except
the type of a few load/extend instructions.
Should not have negative performance implications.
* Switch to yearless copyright per FB policy
* Fix up SPDX-License-Identifier lines in `contrib/linux-kernel` sources
* Add zstd copyright/license header to the `contrib/linux-kernel` sources
* Update the `tests/test-license.py` to check for yearless copyright
* Improvements to `tests/test-license.py`
* Check `contrib/linux-kernel` in `tests/test-license.py`
The most common information that you want to track between begin() and
end() is the timestamp of the begin function, so you can measure the
duration of the (de)compression call. Allow the tracing library to put
this information inside the `ZSTD_TraceCtx`, so it doesn't need to keep
a global map in this case. If a single uint64_t is not enough, the
tracing library can return a unique identifier (like the context
pointer) instead, and use it as a key in a map.
This keeps the simple case simple.
* All copyright lines now have -2020 instead of -present
* All copyright lines include "Facebook, Inc"
* All licenses are now standardized
The copyright in `threading.{h,c}` is not changed because it comes from
zstdmt.
The copyright and license of `divsufsort.{h,c}` is not changed.
Bugs:
* `ZSTD_DCtx_refPrefix()` didn't clear the dictionary after the first
use. Fix and add a test case.
* `ZSTD_DCtx_reset()` always cleared the dictionary. Fix and add a test
case.
* After calling `ZSTD_resetDStream()` you could no longer load a
dictionary, since the stage was set to `zdss_loadHeader`. Fix and add
a test case.
Cleanup:
* Make `ZSTD_initDStream*()` and `ZSTD_resetDStream()` wrap the new
advanced API, and add test cases.
* Document the equivalent of these functions in the advanced API and
document the unstable functions as deprecated.
isolate all logic associated with block decompression
into its own module.
zstd_decompress is still in charge
of context creation/destruction,
frames, headers, streaming, special blocks, etc.
Compressed blocks themselves are now handled within zstd_decompress_block .
