diff options
author | Ganesh Ajjanagadde <gajjanagadde@gmail.com> | 2015-10-18 04:22:59 +0300 |
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committer | Ganesh Ajjanagadde <gajjanagadde@gmail.com> | 2015-10-18 16:22:49 +0300 |
commit | e11e32686fdb21aded1ccf70202f1fffe87bb6a2 (patch) | |
tree | fe5eafdc561ababcf7c3658707259fa840d46514 | |
parent | 9496f565dcc7b5ec5d8d118e492a0637c15617da (diff) |
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 <michael@niedermayer.cc>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
-rw-r--r-- | libavcodec/bitstream.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/libavcodec/bitstream.c b/libavcodec/bitstream.c index 924cc519a2..1acb7a337d 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; |