the variable has only very limited usage,
being only used once at the beginning of the block for prefetching only,
hence the error had no impact on compression ratio.
mostly for maintenance convenience.
Performance wise, there is very little change,
slightly faster for slog 3 & 4,
neutral or very slightly negative for slot 5 & 6.
no idea why visual + clang-cl + appveyor don't like them,
I've not been able to reproduce the issue locally,
but these static assert are very unlikely to deliver a useful signal,
I can't imagine a situation where they will be wrong,
and if they are, then a ton of other things will be broken way before reaching that point.
because mem.h is dropped in the Linux kernel.
Changed macro definition order (gcc/clang/msvc before c11)
due to a limitation in the kernel source builder.
Changed the backup to sizeof(),
reverting to previous behavior when no support of alignof() is detected.
51 MB seems excessive for CI storate and considering the nature of the test.
(note : maybe we should consider using `/tmp` for files generated during tests,
as tmpfs is typically using RAM, thus preserving storage.)
that's clearer than finding the tables somewhere in the middle of `compress.c`.
Also, down the line, it may potentially allows zstd to feature adjusted tables depending on target cpu.
turns out, it's possible to constify MatchState* parameter
in some parts of the binary tree algorithm,
making it a pure read-only parameter,
as opposed to a mutable state.
This is supposed to be helpful for both maintenance and the compiler.
better for large files, and sources with relatively "stable" entropy,
like silesia.tar.
slightly worse for files with rapidly changing entropy,
like Calgary.tar/.
Updated small files tests in fuzzer
used to be necessary to counter-balance the fixed-weight frequency update
which has been recently changed for an adaptive rate (targeting stable starting frequency stats).
This patch is supposed to improve compatibility with less featured tar variants
"when the tar program used does not support historical options (without hyphen) nor the '-z' option."
Patch proposed by Antonio Diaz Diaz
and restored limit to 256 when in 64-bit mode
(it was reduced to 200 to give more room for 32-bit).
This should fix test instability issues
using lot of threads in 32-bit environments.
the new alignment setting is better for gcc-9 and gcc-10
by about ~+5%.
Unfortunately, it's worse for essentially all other compilers.
Make the new alignment setting conditional to gcc-9+.
changed strategy,
now unconditionally prefetch the first 2 cache lines,
instead of cache lines corresponding to the first and last bytes of the match.
This better corresponds to cpu expectation,
which should auto-prefetch following cachelines on detecting the sequential nature of the read.
This is globally positive, by +5%,
though exact gains depend on compiler (from -2% to +15%).
The only negative counter-example is gcc-9.
benchmark results are not progressively displayed on Windows terminal.
For long benchmark sessions, nothing is displayed,
until the end, where everything is flushed.
Force display to be flushed after each update.
Updates happen roughtly every second, or even less,
so it's not a substantial workload.
previous lower limit was 1 MB.
Note : by default, the lowest job size is 2 MB, achieved at level 1.
Even lower job sizes can be achieved by manipulating this value directly,
or manually modifying window sizes to lower amounts.
Updated unit test to ensure that this new limit works fine
(test would fail with previous 1 MB limit).
Any stable API entry point introduced after v1.0
should be documented with its minimum version number.
Since PR fixes this requirement
updating mostly new entry points since v1.4.0
and newly introduced ones for future v1.5.0.
Following #2545,
I noticed that one field in `seq_t` is optional,
and only used in combination with prefetching.
(This may have contributed to static analyzer failure to detect correct initialization).
I then wondered if it would be possible to rewrite the code
so that this optional part is handled directly by the prefetching code
rather than delegated as an option into `ZSTD_decodeSequence()`.
This resulted into this refactoring exercise
where the prefetching responsibility is better isolated into its own function
and `ZSTD_decodeSequence()` is streamlined to contain strictly Sequence decoding operations.
Incidently, due to better code locality,
it reduces the need to send information around,
leading to simplified interface, and smaller state structures.
Yann Collet