C code or compiler built-ins are preferable over inline assembler for
byte-swaps as it allows for better optimisations (e.g. instruction
scheduling) which would otherwise be impossible.
As with f64c2e710f for x86 and Arm,
this removes the inline assembler on GCC (and Clang) since we now
require recent enough compiler versions. This indeed seems to work on
AArch64, SuperH and, if Zbb is enabled, RISC-V. (AVR32 was not tested
since it has no known working compilers at this time.)
If the target supports the Basic bit-manipulation (Zbb) extension, then
the REV8 instruction is available to reverse byte order.
Note that this instruction only exists at the "XLEN" register size,
so we need to right shift the result down to the data width.
If Zbb is not supported, then this patchset does nothing. Support for
run-time detection is left for the future. Currently, there are no
bits in auxv/ELF HWCAP for Z-extensions, so there are no clean ways to
do this.
With these changes, gcc 4.5 and later recognise it as a bswap
and use the proper instructions on ARM and x86. On x86, the
16-bit bswap is recognised from gcc 4.1.
Signed-off-by: Mans Rullgard <mans@mansr.com>
Other parts of FFmpeg use NE (native endian) rather than ME (machine).
This makes it consistent.
Originally committed as revision 24169 to svn://svn.ffmpeg.org/ffmpeg/trunk
The normal byteswap functions might use inline asm which is suboptimal
with constants (and cannot be used in static initialisers), so special
macros for constants only is needed.
We should not rely on the gcc __builtin_constant_p() test since it is
not always available.
Originally committed as revision 22990 to svn://svn.ffmpeg.org/ffmpeg/trunk
Passing an explicit filename to this command is only necessary if the
documentation in the @file block refers to a file different from the
one the block resides in.
Originally committed as revision 22921 to svn://svn.ffmpeg.org/ffmpeg/trunk
This reduces the number of false dependencies on header files and
speeds up compilation.
Originally committed as revision 22407 to svn://svn.ffmpeg.org/ffmpeg/trunk
Otherwise doxygen complains about ambiguous filenames when files exist
under the same name in different subdirectories.
Originally committed as revision 16912 to svn://svn.ffmpeg.org/ffmpeg/trunk
Neither the asm() nor the __asm__() keyword is part of the C99
standard, but while GCC accepts the former in C89 syntax, it is not
accepted in C99 unless GNU extensions are turned on (with -fasm). The
latter form is accepted in any syntax as an extension (without
requiring further command-line options).
Sun Studio C99 compiler also does not accept asm() while accepting
__asm__(), albeit reporting warnings that it's not valid C99 syntax.
Originally committed as revision 15627 to svn://svn.ffmpeg.org/ffmpeg/trunk
Consistently apply this rule: the guard name is obtained from the
filename by stripping the leading "lib", converting '/' and '.' to
'_' and uppercasing the resulting name. Guard names in the root
directory have to be prefixed by "FFMPEG_".
Originally committed as revision 15120 to svn://svn.ffmpeg.org/ffmpeg/trunk
Patch by Zuxy Meng: zuxy meng gmail com
Original thread:
[FFmpeg-devel] [PATCH] Pure, const and malloc attributes to libavutil
Date: 03/18/2008 6:09 AM
Originally committed as revision 12489 to svn://svn.ffmpeg.org/ffmpeg/trunk
200% faster on BF537 compiled with gcc 4.1.
patch by Marc Hoffman, mmh pleasantst com
Originally committed as revision 8802 to svn://svn.ffmpeg.org/ffmpeg/trunk
