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44e1b60c6a
Rather than having two uops for the C reference code and a separate
uop for the x86 backend, we can just implement the C reference
using the same register-register assignment logic.
This results in only slightly worse codegen, since the compiler is
smart enough to eliminate the unnecessary copies.
The main downside is the fact that we need to allocate extra stack space
to back-fill the remaining (unused) pointers. In theory, we could do this
more efficiently by re-using unused *input* registers directly, but that
would require a lot of reliance on compile-time constant folding teasing
apart the entire register index tracking loop and duplicate check, so this
is a useful middle ground.
On platforms like x86, we still don't care about the PERMUTE vs
COPY distinction, but it's also harmless (2-3 extra lines to
instantiate the underlying MOVE macro on both uop variants).
Finally, we need to add a mask to the move uops to keep track of which
outputs are actually needed (especially for checkasm). Though it does result
in the rather unfortunate downside that it bloats the names of the uop
names.
The op lists change to reflect the new representation, e.g.:
rgb24 16x16 -> bgr24 16x16:
[ u8 +++X] SWS_OP_READ : 3 elem(s) packed >> 0
min: {0 0 0 _}, max: {255 255 255 _}
[ u8 +++X] SWS_OP_SWIZZLE : 2103
min: {0 0 0 _}, max: {255 255 255 _}
[ u8 XXXX] SWS_OP_WRITE : 3 elem(s) packed >> 0
('X' unused, 'z' byteswapped, '=' copied, '$' const, '+' integer, '0' zero)
translated micro-ops:
u8_read_packed_xyz
- u8_permute_zyxw
+ u8_permute_xyzw_txz_xzt
u8_write_packed_xyz
Signed-off-by: Niklas Haas <git@haasn.dev>
FFmpeg README
FFmpeg is a collection of libraries and tools to process multimedia content such as audio, video, subtitles and related metadata.
Libraries
libavcodecprovides implementation of a wider range of codecs.libavformatimplements streaming protocols, container formats and basic I/O access.libavutilincludes hashers, decompressors and miscellaneous utility functions.libavfilterprovides means to alter decoded audio and video through a directed graph of connected filters.libavdeviceprovides an abstraction to access capture and playback devices.libswresampleimplements audio mixing and resampling routines.libswscaleimplements color conversion and scaling routines.
Tools
- ffmpeg is a command line toolbox to manipulate, convert and stream multimedia content.
- ffplay is a minimalistic multimedia player.
- ffprobe is a simple analysis tool to inspect multimedia content.
- Additional small tools such as
aviocat,ismindexandqt-faststart.
Documentation
The offline documentation is available in the doc/ directory.
The online documentation is available in the main website and in the wiki.
Examples
Coding examples are available in the doc/examples directory.
License
FFmpeg codebase is mainly LGPL-licensed with optional components licensed under GPL. Please refer to the LICENSE file for detailed information.
Contributing
Patches should be submitted to the ffmpeg-devel mailing list using
git format-patch or git send-email. Github pull requests should be
avoided because they are not part of our review process and will be ignored.