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
