Commit Graph

6 Commits

Author SHA1 Message Date
Lasse Collin f644473a21 liblzma: Add fast CRC64 for 32/64-bit x86 using SSSE3 + SSE4.1 + CLMUL.
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
2022-11-14 23:05:46 +02:00
Lasse Collin a12b13c5f0 liblzma: Silence clang -Wmissing-variable-declarations. 2019-06-24 23:45:21 +03:00
Lasse Collin 02ddf09bc3 Put the interesting parts of XZ Utils into the public domain.
Some minor documentation cleanups were made at the same time.
2009-04-13 11:27:40 +03:00
Lasse Collin c324325f9f Removed src/liblzma/common/sysdefs.h symlink, which was
annoying, because "make dist" put two copies of sysdefs.h
into the tarball instead of the symlink.
2008-04-25 13:58:56 +03:00
Lasse Collin 4e7e54c4c5 Introduced compatibility with systems that have pre-C99
or no inttypes.h. This is useful when the compiler has
good enough support for C99, but libc headers don't.

Changed liblzma API so that sys/types.h and inttypes.h
have to be #included before #including lzma.h. On systems
that don't have C99 inttypes.h, it's the problem of the
applications to provide the required types and macros
before #including lzma.h.

If lzma.h defined the missing types and macros, it could
conflict with third-party applications whose configure
has detected that the types are missing and defined them
in config.h already. An alternative would have been
introducing lzma_uint32 and similar types, but that would
just be an extra pain on modern systems.
2008-01-06 16:27:41 +02:00
Lasse Collin 5d018dc035 Imported to git. 2007-12-09 00:42:33 +02:00