Ryan Lefkowitz [Mon, 15 Sep 2025 22:20:01 +0000 (18:20 -0400)]
🔧 Fix memory leak in pthread init functions on failure
When pthread_mutex_init() or pthread_cond_init() fails in the debug
implementation (DEBUGLEVEL >= 1), the previously allocated memory was
not freed, causing a memory leak.
This fix ensures that allocated memory is properly freed when pthread
initialization functions fail, preventing resource leaks in error
conditions.
The issue affects:
- ZSTD_pthread_mutex_init() at lib/common/threading.c:146
- ZSTD_pthread_cond_init() at lib/common/threading.c:167
This is particularly important for long-running applications or
scenarios with resource constraints where pthread initialization
might fail due to system limits.
Update manual about the default value of `-T#`/`--threads=#`
The section about `ZSTD_NBTHREADS` already explains the default number of
threads, since it changed from 1 (commit 17beeb5). But the option description
for `-T#`/`--threads=#` incorrectly said the default was still 1.
I noticed this when I found compression slower with `-T1` than without it.
Benjamin Gilbert [Thu, 28 Aug 2025 23:50:34 +0000 (18:50 -0500)]
meson: Call meson.override_dependency() if Meson is new enough
This tells Meson that we intend libzstd_dep to be used by a parent project
if the parent looks for a dependency named "libzstd". Without this, the
mapping from "libzstd" to our variable libzstd_dep must be encoded in the
Meson wrap file or in the parent's meson.build.
Brad Smith [Tue, 19 Aug 2025 13:23:38 +0000 (09:23 -0400)]
Check for build environment instead of just _GNU_SOURCE
Fixes the build on OpenBSD and NetBSD. It is too easy for _GNU_SOURCE
to be defined even on non-Linux systems. Found via py-zstandard with
the embedded copy of zstandard and Python defines _GNU_SOURCE.
Also simplify the Linux checking, there is no need to check the rest
of the symbol names.
replaced by one vs2025 runner,
which is badly named since it still running MSVC 2022,
but it's a good test that shows that the matrix is able to handle multiple MSVC versions.
AArch64: Add Neon path for convertSequences_noRepcodes
Add a 4-way Neon implementation for the convertSequences_noRepcodes
function. Remove 'static' keywords from all of its implementations to
be able to add unit tests.
Relative performance to Clang-18 using: `./fullbench -b18 -l5 enwik5`
Add a faster scalar implementation of ZSTD_get1BlockSummary which
removes the data dependency of the accumulators in the hot loop to
leverage the superscalar potential of recent out-of-order CPUs.
The new algorithm leverages SWAR (SIMD Within A Register) methodology
to exploit the capabilities of 64-bit architectures. It achieves this
by packing two 32-bit data elements into a single 64-bit register,
enabling parallel operations on these subcomponents while ensuring
that the 32-bit boundaries prevent overflow, thereby optimizing
computational efficiency.
Corresponding unit tests are included.
Relative performance to GCC-13 using: `./fullbench -b19 -l5 enwik5`
Rose [Tue, 24 Jun 2025 18:05:08 +0000 (14:05 -0400)]
Check for job before releasing
ZSTDMT_freeCCtx calls ZSTDMT_releaseAllJobResources, but ZSTDMT_releaseAllJobResources may be called when ZSTDMT_freeCCtx is called when initialization fails, resulting in a NULL pointer dereference.
Arpad Panyik [Tue, 24 Jun 2025 11:26:58 +0000 (11:26 +0000)]
AArch64: Improve ZSTD_decodeSequence performance
LLVM's alias-analysis sometimes fails to see that a static-array member
of a struct cannot alias other members. This patch:
- Reduces array accesses via struct indirection to aid load/store alias
analysis under Clang.
- Converts dynamic array indexing into conditional-move arithmetic,
eliminating branches and extra loads/stores on out-of-order CPUs.
- Reloads the bitstream only when match-length bits are consumed
(assuming each reload only needs to happen once per match-length
read), improving branch-prediction rates.
- Removes the UNLIKELY() hint, which recent compilers already handle
well without cost.
Decompression uplifts on a Neoverse V2 system, using Zstd-1.5.8
compiled with "-O3 -march=armv8.2-a+sve2":
Arpad Panyik [Fri, 20 Jun 2025 15:29:17 +0000 (15:29 +0000)]
AArch64: Enhance struct access in Huffman decode 2X
In the multi-stream multi-symbol Huffman decoder GCC generates
suboptimal code - emitting more loads for HUF_DEltX2 struct member
accesses. Forcing it to use 32-bit loads and bit arithmetic to extract
the necessary parts (UBFX) improves the overall decode speed.
Also avoid integer type conversions in the symbol decodes, which
leads to better instruction selection in table lookup accesses.
On AArch64 the decoder no longer runs into register-pressure limits,
so we can simplify the hot path and improve throughput
Decompression uplifts on a Neoverse V2 system, using Zstd-1.5.8
compiled with "-O3 -march=armv8.2-a+sve2":
Arpad Panyik [Wed, 11 Jun 2025 12:19:42 +0000 (12:19 +0000)]
Add unit tests for HIST_count_wksp
The following tests are included:
- Empty input scenario test.
- Workspace size and alignment tests.
- Symbol out-of-range tests.
- Cover multiple input sizes, vary permitted maximum symbol
values, and include diverse symbol distributions.
These tests verifies count table correctness, maxSymbolValuePtr
updates, and error-handling paths. It enables automated regression
of core histogram logic as well.
jinyaoguo [Thu, 12 Jun 2025 23:52:58 +0000 (19:52 -0400)]
Ensure BMK_timedFnState is always freed in benchMem
When an error occurs in BMK_isSuccessful_runOutcome, the code
previously skipped the call to BMK_freeTimedFnState(tfs),
leaking the allocated tfs object.
Fiexed by calling BMK_freeTimedFnState(tfs) before goto _cleanOut.
Arpad Panyik [Wed, 11 Jun 2025 12:14:22 +0000 (12:14 +0000)]
AArch64: Add SVE2 implementation of histogram computation
The existing scalar implementation uses a 4-way pipelined histogram
calculation which is very efficient on out-of-order CPUs. However,
this can be further accelerated using the SVE2 HISTSEG instructions -
which compute a histogram for 16 byte chunks in a vector register.
On a system with 128-bit vectors (VL128) we need 16 HISTSEG executions
to compute the histogram for the whole symbol space (0..255) of 16
bytes input. However we can only accumulate 15 of such 16 byte strips
before possible overflow. So we need to extend and save the 8-bit
histogram accumulators to 16-bit after every 240 byte chunks of input.
To store all in registers we would need 32 128-bit registers. Longer
SVE2 vectors could help here, if such machines become available.
The maximum input block size in Zstd is 128 KiB, so 16-bit accumulators
would not be enough. However an LZ pass will prepend the histogram
calculation, so it is impossible (my assumption) to overflow the 16-bit
accumulators.
The symbol distribution is also not uniform, the lower values are more
common, so we used a 3 pass algorithm to prevent stack spilling. In the
first pass we only compute histograms for 64 symbols (4-way SIMD) while
also computing the maximum symbol value. If we have symbol values
larger than 64 we start the second pass to compute the next 96 elements
of the histogram. The final pass calculates the remaining part of the
histogram (256 symbols in total) if needed. This split of histogram
generation gave the best overall results for performance.
This implementation is the best performing of a number of different
cache blocking schemes tested.
Compression uplifts on a Neoverse V2 system, using Zstd-1.5.8
(e26dde3d) as a baseline, compiled with "-O3 -march=armv8.2-a+sve2":
projects / thirdparty / zstd.git / log
