pow is a very wasteful function for this purpose. A low hanging fruit
would be simply to replace with exp2f, and that does yield some speedup.
However, there are 2 drawbacks of this:
1. It does not exploit the integer nature of the argument.
2. (minor) Some platforms lack a proper exp2f routine, making benefits available
only to non broken libm.
3. exp2f does not solve the same issue that plagues pow, namely terrible
worst case performance. This is a fundamental issue known as the
"table-maker's dilemma" recognized by Prof. Kahan himself and
subsequently elaborated and researched by many others. All this is clear from benchmarks below.
This exploits the IEEE-754 format to get very good performance even in
the worst case for integer powers of 2. This solves all the issues noted
above. Function tested with clang usan over [-1000, 1000] (beyond range of
relevance for this, which is [-255, 255]), patch itself with FATE.
Benchmarks obtained on x86-64, Haswell, GNU-Linux via 10^5 iterations of
the pow call, START/STOP, and command ffplay ~/samples/jpeg2000/chiens_dcinema2K.mxf.
Low number of runs also given to prove the point about worst case:
pow:
216270 decicycles in pow, 1 runs, 0 skips
110175 decicycles in pow, 2 runs, 0 skips
56085 decicycles in pow, 4 runs, 0 skips
29013 decicycles in pow, 8 runs, 0 skips
15472 decicycles in pow, 16 runs, 0 skips
8689 decicycles in pow, 32 runs, 0 skips
5295 decicycles in pow, 64 runs, 0 skips
3599 decicycles in pow, 128 runs, 0 skips
2748 decicycles in pow, 256 runs, 0 skips
2304 decicycles in pow, 511 runs, 1 skips
2072 decicycles in pow, 1022 runs, 2 skips
1963 decicycles in pow, 2044 runs, 4 skips
1894 decicycles in pow, 4091 runs, 5 skips
1860 decicycles in pow, 8184 runs, 8 skips
exp2f:
134140 decicycles in pow, 1 runs, 0 skips
68110 decicycles in pow, 2 runs, 0 skips
34530 decicycles in pow, 4 runs, 0 skips
17677 decicycles in pow, 8 runs, 0 skips
9175 decicycles in pow, 16 runs, 0 skips
4931 decicycles in pow, 32 runs, 0 skips
2808 decicycles in pow, 64 runs, 0 skips
1747 decicycles in pow, 128 runs, 0 skips
1208 decicycles in pow, 256 runs, 0 skips
952 decicycles in pow, 512 runs, 0 skips
822 decicycles in pow, 1024 runs, 0 skips
765 decicycles in pow, 2047 runs, 1 skips
722 decicycles in pow, 4094 runs, 2 skips
693 decicycles in pow, 8190 runs, 2 skips
exp2fi:
2740 decicycles in pow, 1 runs, 0 skips
1530 decicycles in pow, 2 runs, 0 skips
955 decicycles in pow, 4 runs, 0 skips
622 decicycles in pow, 8 runs, 0 skips
477 decicycles in pow, 16 runs, 0 skips
368 decicycles in pow, 32 runs, 0 skips
317 decicycles in pow, 64 runs, 0 skips
291 decicycles in pow, 128 runs, 0 skips
277 decicycles in pow, 256 runs, 0 skips
268 decicycles in pow, 512 runs, 0 skips
265 decicycles in pow, 1024 runs, 0 skips
263 decicycles in pow, 2048 runs, 0 skips
263 decicycles in pow, 4095 runs, 1 skips
260 decicycles in pow, 8191 runs, 1 skips
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
This fixes out-of-bounds reads in avoid_clipping.
Reviewed-by: Rostislav Pehlivanov <atomnuker@gmail.com>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
In the merge commit 78265fcfeee153e5e26ad4dbc7831a84ade447d6 this behaviour
was broken and the CORRUPT flag would never ever be set on a frame. However
the flag on the AVCodecContext was taken into account properly, including
AV_CODEC_FLAG2_SHOW_ALL.
The reason for this was that the recovered field of the next output picture
was always set to TRUE whenever one of the two AVCodecContext flags was set,
which made it impossible to detect later, before outputting, if the frame was
really recovered or not. Now don't set it to TRUE unless the frame is really
recovered and check the AVCodecContext flags right before outputting.
Signed-off-by: Sebastian Dröge <sebastian@centricular.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
With only 7 coefficients per short window at most the extra precision
makes a difference and seems to reduce crackling and stddev even
further.
Signed-off-by: Rostislav Pehlivanov <atomnuker@gmail.com>
* commit 'b805482b1fba1d82fbe47023a24c9261f18979b6':
aac: Provide more information on the failure message
Merged-by: Hendrik Leppkes <h.leppkes@gmail.com>
* commit '1077d8c8455b27688de37cd04f8cc253fb37944d':
configure: Add -framework CoreVideo when building the avfoundation indev
Merged-by: Hendrik Leppkes <h.leppkes@gmail.com>
* commit 'bf12a81cc67d62dd45c58e29fa0e9177331cc151':
configure: Replace `pr` since it is not provided by busybox
Not merged as requested by Timothy Gu.
Merged-by: Hendrik Leppkes <h.leppkes@gmail.com>
* commit '5f3a081b42b84404a40a52c80ef7a354cf048c56':
avi: Spin out the logic to position to the next non-interleaved stream
Merged-by: Hendrik Leppkes <h.leppkes@gmail.com>
Don't print a warning when dcadec_context_filter() returns positive
warning code. Most relevant warnings are now output through the callback
function.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
Take request_channel_layout as a hint and don't force 2.0 downmix by
using both the 2CH and 6CH flags together.
Remove warnings about missing coefficients because they are no longer
relevant.
Honor AV_CH_LAYOUT_NATIVE and make it possible for native DTS channel
layout to be output.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
* commit 'f023d57d355ff3b917f1aad9b03db5c293ec4244':
lavc: G.723.1 encoder
Split existing FFmpeg G.723.1 encoder into a new file.
Merged-by: Hendrik Leppkes <h.leppkes@gmail.com>
* commit '165cc6fb9defcd79fd71c08167f3e8df26b058ff':
g723_1: Move sharable functions to a separate file
Merged-by: Hendrik Leppkes <h.leppkes@gmail.com>
* commit 'aac996cc01042194bf621d845bbe684549b5882e':
g723_1: Rename files to better reflect their purpose
Merged-by: Hendrik Leppkes <h.leppkes@gmail.com>
* commit 'b74b88f30da2389f333a31815d8326d5576d3331':
g723_1: Handle values at the ends of the table in lsp2lpc()
Merged-by: Hendrik Leppkes <h.leppkes@gmail.com>
* commit 'a0fa6d06b848f26b16ba12f0a9a4a85b93ab8022':
matroska: Warn when metadata references a non-existent element
Merged-by: Hendrik Leppkes <h.leppkes@gmail.com>
* commit '4f979418c723652ad4e43115118c57a44bd46b52':
avfoundation: Simple capture
Not merged on request by Thilo Borgmann, original author of the
AVFoundation capture in FFmpeg.
Merged-by: Hendrik Leppkes <h.leppkes@gmail.com>
Fix a dead lock under certain conditions. Let's assume we have a queue of 1
message max, 2 senders, and 1 receiver.
Scenario (real record obtained with debug added):
[...]
SENDER #0: acquired lock
SENDER #0: queue is full, wait
SENDER #1: acquired lock
SENDER #1: queue is full, wait
RECEIVER: acquired lock
RECEIVER: reading a msg from the queue
RECEIVER: signal the cond
RECEIVER: acquired lock
RECEIVER: queue is empty, wait
SENDER #0: writing a msg the queue
SENDER #0: signal the cond
SENDER #0: acquired lock
SENDER #0: queue is full, wait
SENDER #1: queue is full, wait
Translated:
- initially the queue contains 1/1 message with 2 senders blocking on
it, waiting to push another message.
- Meanwhile the receiver is obtaining the lock, read the message,
signal & release the lock. For some reason it is able to acquire the
lock again before the signal wakes up one of the sender. Since it
just emptied the queue, the reader waits for the queue to fill up
again.
- The signal finally reaches one of the sender, which writes a message
and then signal the condition. Unfortunately, instead of waking up
the reader, it actually wakes up the other worker (signal = notify
the condition just for 1 waiter), who can't push another message in
the queue because it's full.
- Meanwhile, the receiver is still waiting. Deadlock.
This scenario can be triggered with for example:
tests/api/api-threadmessage-test 1 2 100 100 1 1000 1000
One working solution is to make av_thread_message_queue_{send,recv}()
call pthread_cond_broadcast() instead of pthread_cond_signal() so both
senders and receivers are unlocked when work is done (be it reading or
writing).
This second solution replaces the condition with two: one to notify the
senders, and one to notify the receivers. This prevents senders from
notifying other senders instead of a reader, and the other way around.
It also avoid broadcasting to everyone like the first solution, and is,
as a result in theory more optimized.
