ffmpeg | branch: master | Ganesh Ajjanagadde <gajjanaga...@gmail.com> | Sat Oct 17 21:22:59 2015 -0400| [e11e32686fdb21aded1ccf70202f1fffe87bb6a2] | committer: Ganesh Ajjanagadde
avcodec/bitstream: replace qsort with AV_QSORT Commit 3a0a2f33a6c955823fa4fb12c0b49cd29a496659 claims large performance advantages for AV_QSORT over libc's qsort. The reason is that I suspect that libc's qsort (at least on non LTO builds, like the typical FFmpeg config) can't inline the comparison callback: https://stackoverflow.com/questions/5290695/is-there-any-way-a-c-c-compiler-can-inline-a-c-callback-function. AV_QSORT has two things going for it: 1. The guaranteed inlining of qsort itself. This yields a negligible boost that may be ignored. 2. The more serious possibility of potentially allowing the comparison function to be inlined - this is likely responsible for the large boosts reported. There is a comment explaining that this is a place that could use some performance improvement. Thus AV_QSORT is used to achieve that. Benchmarks deemed unnecessary due to existing claims about AV_QSORT. Tested with FATE. Reviewed-by: Michael Niedermayer <mich...@niedermayer.cc> Signed-off-by: Ganesh Ajjanagadde <gajjanaga...@gmail.com> > http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=e11e32686fdb21aded1ccf70202f1fffe87bb6a2 --- libavcodec/bitstream.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/libavcodec/bitstream.c b/libavcodec/bitstream.c index 924cc51..1acb7a3 100644 --- a/libavcodec/bitstream.c +++ b/libavcodec/bitstream.c @@ -30,6 +30,7 @@ #include "libavutil/atomic.h" #include "libavutil/avassert.h" +#include "libavutil/qsort.h" #include "avcodec.h" #include "internal.h" #include "mathops.h" @@ -333,7 +334,7 @@ int ff_init_vlc_sparse(VLC *vlc_arg, int nb_bits, int nb_codes, } COPY(buf[j].bits > nb_bits); // qsort is the slowest part of init_vlc, and could probably be improved or avoided - qsort(buf, j, sizeof(VLCcode), compare_vlcspec); + AV_QSORT(buf, j, struct VLCcode, compare_vlcspec); COPY(buf[j].bits && buf[j].bits <= nb_bits); nb_codes = j; _______________________________________________ ffmpeg-cvslog mailing list ffmpeg-cvslog@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-cvslog
