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This affects only 32-bit x86 builds. x86-64 is OK as is.
I still cannot easily test this myself. The reporter has tested
this and it passes the tests included in the CMake build and
performance is good: raw CRC64 is 2-3 times faster than the
C version of the slice-by-four method. (Note that liblzma doesn't
include a MSVC-compatible version of the 32-bit x86 assembly code
for the slice-by-four method.)
Thanks to Iouri Kharon for figuring out a fix, testing, and
benchmarking.
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This reverts commit 36edc65ab4cf10a131f239acbd423b4510ba52d5.
It was reported that it wasn't a good enough fix and MSVC
still produced (different kind of) bad code when building
for 32-bit x86 if optimizations are enabled.
Thanks to Iouri Kharon.
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I haven't tested with MSVC myself and there doesn't seem to be
information about the problem online, so I'm relying on the bug report.
Thanks to Iouri Kharon for the bug report and the patch.
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It also works on E2K as it supports these intrinsics.
On x86-64 runtime detection is used so the code keeps working on
older processors too. A CLMUL-only build can be done by using
-msse4.1 -mpclmul in CFLAGS and this will reduce the library
size since the generic implementation and its 8 KiB lookup table
will be omitted.
On 32-bit x86 this isn't used by default for now because by default
on 32-bit x86 the separate assembly file crc64_x86.S is used.
If --disable-assembler is used then this new CLMUL code is used
the same way as on 64-bit x86. However, a CLMUL-only build
(-msse4.1 -mpclmul) won't omit the 8 KiB lookup table on
32-bit x86 due to a currently-missing check for disabled
assembler usage.
The configure.ac check should be such that the code won't be
built if something in the toolchain doesn't support it but
--disable-clmul-crc option can be used to unconditionally
disable this feature.
CLMUL speeds up decompression of files that have compressed very
well (assuming CRC64 is used as a check type). It is know that
the CLMUL code is significantly slower than the generic code for
tiny inputs (especially 1-8 bytes but up to 16 bytes). If that
is a real-world problem then there is already a commented-out
variant that uses the generic version for small inputs.
Thanks to Ilya Kurdyukov for the original patch which was
derived from a white paper from Intel [1] (published in 2009)
and public domain code from [2] (released in 2016).
[1] https://www.intel.com/content/dam/www/public/us/en/documents/white-papers/fast-crc-computation-generic-polynomials-pclmulqdq-paper.pdf
[2] https://github.com/rawrunprotected/crc
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Using the aligned methods requires more care to ensure that
the address really is aligned, so it's nicer if the aligned
methods are prefixed. The next commit will remove the unaligned_
prefix from the unaligned methods which in liblzma are used in
more places than the aligned ones.
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This replaces bswap.h and integer.h.
The tuklib module uses <byteswap.h> on GNU,
<sys/endian.h> on *BSDs and <sys/byteorder.h>
on Solaris, which may contain optimized code
like inline assembly.
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Some minor documentation cleanups were made at the same time.
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other compilers than MinGW. This may hurt readability
of the API headers slightly, but I don't know any
better way to do this.
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Half of developers were already forgetting to use these
functions, which could have caused total breakage in some future
liblzma version or even now if --enable-small was used. Now
liblzma uses pthread_once() to do the initializations unless
it has been built with --disable-threads which make these
initializations thread-unsafe.
When --enable-small isn't used, liblzma currently gets needlessly
linked against libpthread (on systems that have it). While it is
stupid for now, liblzma will need threads in future anyway, so
this stupidity will be temporary only.
When --enable-small is used, different code CRC32 and CRC64 is
now used than without --enable-small. This made the resulting
binary slightly smaller, but the main reason was to clean it up
and to handle the lack of lzma_init_check().
The pkg-config file lzma.pc was renamed to liblzma.pc. I'm not
sure if it works correctly and portably for static linking
(Libs.private includes -pthread or other operating system
specific flags). Hopefully someone complains if it is bad.
lzma_rc_prices[] is now included as a precomputed array even
with --enable-small. It's just 128 bytes now that it uses uint8_t
instead of uint32_t. Smaller array seemed to be at least as fast
as the more bloated uint32_t array on x86; hopefully it's not bad
on other architectures.
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