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1cb7fd317c
encode_block() in svq1enc.c looks like the following:
static int encode_block(int block[7][256], int level)
{
int best_score = 0;
for (unsigned x = 0; x < level; x++) {
int v = block[1][x];
block[level][x] = 0;
best_score += v * v;
}
if (level > 0 && best_score > 64) {
int score = 0;
score += encode_block(block, level - 1);
score += encode_block(block, level - 1);
if (score < best_score) {
best_score = score;
}
}
return best_score;
}
When called from outside of encode_block(), it is always called with
level == 5.
This triggers a bug [1] in GCC: On -O3, it creates eight clones of
encode_block with different values of level inlined into it. The clones
with negative values are of course useless*, but they also lead to
-Warray-bounds warnings, because they access block[-1].
This has been mitigated in GCC 12: It no longer creates clones
for parameters that it knows are impossible. Somehow switching levels
to unsigned makes GCC know this. Therefore this commit does this.
(For GCC 11, this changes the warning to "array subscript 4294967295 is
above array bounds" from "array subscript -1 is below array bounds".)
[1]: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102513
*: These clones can actually be discarded when compiling with
-ffunction-sections.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
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.