They're marked constinit, but constinit does not imply const. Since
they're not supposed to be modified, mark them const too.
Closesscylladb/scylladb#25539
C++20 introduced two new attributes--likely and unlikely--that
function as a built-in replacement for __builtin_expect implemented
in various compilers. Since it makes code easier to read and it's
an integral part of the language, there's no reason to not use it
instead.
Closesscylladb/scylladb#24786
these unused includes were identifier by clang-include-cleaner. after
auditing these source files, all of the reports have been confirmed.
please note, because quite a few source files relied on
`utils/to_string.hh` to pull in the specialization of
`fmt::formatter<std::optional<T>>`, after removing
`#include <fmt/std.h>` from `utils/to_string.hh`, we have to
include `fmt/std.h` directly.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Fix a typo introduced by the the recent patch fixing the spelling of
Barrett. The patch introduced a typo in the aarch64 version of the code,
which wasn't found by promotion, as that only builds on X86_64.
Closes#12006
As P. T. Barnoom famously said, "write what you like but spell my name
correctly". Following that, we correct the spelling of Barrett's name
in the source tree.
Closes#11989
By now the crc combine tables are generated at compile time,
but still in a separate code generation step. We now eliminate
the code generation step and instead link the global variables
directly into the main executable. The global variables have
been conveniently named exactly as the code generation step
names them, so we don't need to touch any users.
Move the tables into global constinit variables that are
generated at compile time. Note the code that creates
the generated crc32_combine_table.cc is still called; it
transorms compile-time generated tables into a C++ source
that contains the same values, as literals.
If we generate a diff between gen/utils/gz/crc_combine_table.cc
before this series and after this patch, we see the only change
in the file is the type of the variable (which changed to
std::array), proving our constexpr code is correct.
Move the code to a constexpr function, so we can later generate the tables at
compile time. Note that although the function is constexpr, it is still
evaluated at runtime, since the calling function (main()) isn't constexpr
itself.
A "pow table" is used to generate the Barrett fold tables. Extract its
code into a constexpr function so we can later generate the fold tables
at compile time.
C arrays cannot be returned from functions and therefore aren't suitable
for constexpr processing. std::array<> is a regular value and so is
constexpr friendly.
If the len2 argument to crc32_combine() is zero, then the crc2
argument must also be zero.
fast_crc32_combine() explicitly checks for len2==0, in which case it
ignores crc2 (which is the same as if it were zero).
zlib's crc32_combine() used to have that check prior to version
1.2.12, but then lost it, making its necessary for callers to be more
careful.
Also add the len2==0 check to the dummy fast_crc32_combine()
implementation, because it delegates to zlib's.
Signed-off-by: Michael Livshin <michael.livshin@scylladb.com>
Closes#10731
Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.
Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.
The changes we applied mechanically with a script, except to
licenses/README.md.
Closes#9937
gcc 10 tightened its C++ includes to no longer provide ssize_t,
so we must get it from a C header instead.
Message-Id: <20200129205912.21139-1-avi@scylladb.com>
gen_crc_combine_table is now executed on every build, so it should not
fail on unsupported archs. The generated file will not contain data,
but this is fine since it should not be used.
Another problem is that u32 and u64 aliases were not visible in the #else
branch in crc_combine.cc
Message-Id: <1543864425-5650-1-git-send-email-tgrabiec@scylladb.com>
zlib's crc32_combine() is not very efficient. It is faster to re-combine
the buffer using crc32(). It's still substantial amount of work which
could be avoided.
This patch introduces a fast implementation of crc32_combine() which
uses a different algorithm than zlib. It also utilizes intrinsics for
carry-less multiplication instruction to perform the computation faster.
The details of the algorithm can be found in code comments.
Performance results using perf_checksum and second buffer of length 64 KiB:
zlib CRC32 combine: 38'851 ns
libdeflate CRC32: 4'797 ns
fast_crc32_combine(): 11 ns
So the new implementation is 3500x faster than zlib's, and 417x faster than
re-checksumming the buffer using libdeflate.
Tested on i7-5960X CPU @ 3.00GHz
Performance was also evaluated using sstable writer benchmark:
perf_fast_forward --populate --sstable-format=mc --data-directory /tmp/perf-mc \
--value-size=10000 --rows 1000000 --datasets small-part
It yielded 9% improvement in median frag/s (129'055 vs 117'977).
gen_crc_combine_table.cc will be run during build to produce tables
with precomputed polynomials (4 x 256 x u32). The definitions will
reside in:
build/<mode>/gen/utils/gz/crc_combine_table.cc
It takes 20ms to generate on my machine.
The purpose of those polynomials will be explained in crc_combine.cc
