exp10 is a function available in GNU libm. Looks like no other common
libm has it. This adds support for it to FFmpeg.
There are essentially 2 ways of handling the fallback:
1. Using pow(10, x)
2. Using exp2(M_LOG2_10 * x).
First one represents a Pareto improvement, with no speed or accuracy
regression anywhere, but speed improvement limited to GNU libm.
Second one represents a slight accuracy loss (relative error ~ 1e-13)
for non GNU libm. Speedup of > 2x is obtained on non GNU libm platforms,
~30% on GNU libm. These are "average case numbers", another benefit is
the lack of triggering of the well-known terrible worst case paths
through pow.
Based on reviews, second one chosen. Comment added accordingly.
Reviewed-by: Hendrik Leppkes <h.leppkes@gmail.com>
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Reviewed-by: Ronald S. Bultje <rsbultje@gmail.com>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
complex is not available on all platforms. Furthermore, it is trivial to
rewrite complex number expressions to real arithmetic, and in fact
sometimes advantageous for performance reasons: by wrapping as a complex,
one forces a particular Cartesian representation that is not necessarily optimal for the purpose.
Configure dependencies also removed, and aemphasis is now available across
all platforms.
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
Fixes a specific srt sample, which has an event with negative duration.
libavcodec will convert an event with negative duration to an ASS event
which will be displayed forever, which is not wanted here.
Treat negative duration always as unknown duration instead, and show it
until the next subtitle event.
This fixes an out-of-bounds read introduced in commit 0379603.
Reviewed-by: Kieran Kunhya <kierank@obe.tv>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
A negative bits_per_coded_sample doesn't make sense.
If it is too large, the size calculation for av_get_packet overflows,
resulting in allocation of a too small buffer.
Also make sure width and height are sane.
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
Instead of calling the input filter request_frame() method,
ff_request_frame() now marks the link and returns immediately.
buffersink is changed to activate the marked filters until
a frame is obtained.
The status field can carry any error code instead of just EOF.
Also only update it through a wrapper function and provide a timestamp.
Update the few filters that used it directly.
Applications are not supposed to mess with links,
they should close the sinks.
Furthermore, this function does not distinguish what end
of the link caused the close and does not have a timestamp.
This field is used for fast comparison between link ages,
it is in AV_TIME_BASE units, in other words microseconds,
µs =~ us.
Renaming it allows a second field in link time base units.
Fix possible SF delta violation that would cause an
eventual assertion failure in some corner cases (esp
on very low bitrates) when marking bands for PNS due
to misuse of the sf_delta utilities
'erf' is far from the best name for a variable and is not very
descriptive since the actual variable points to the comparitively best
IS phase. Therefore rename it to 'best'.
Signed-off-by: Rostislav Pehlivanov <atomnuker@gmail.com>
Source code is from Boost:
http://www.boost.org/doc/libs/1_46_1/boost/math/special_functions/erf.hpp
with appropriate modifications for FFmpeg.
Tested on interval -6 to 6 (beyond which it saturates), +/-NAN, +/-INFINITY
under -fsanitize=undefined on clang to test for possible undefined behavior.
This function turns out to actually be essentially as accurate and faster than the
libm (GNU/BSD's/Mac OS X), and I can think of 3 reasons why upstream
does not use this:
1. They are not aware of it.
2. They are concerned about licensing - this applies especially to GNU
libm.
3. They do not know and/or appreciate the benefits of rational
approximations over polynomial approximations. Boost uses them to great
effect, see e.g swr/resample for bessel derived from them, which is also
similarly superior to libm variants.
First, performance.
sample benchmark (clang -O3, Haswell, GNU/Linux):
3e8 values evenly spaced from 0 to 6
time (libm):
./test 13.39s user 0.00s system 100% cpu 13.376 total
time (boost based):
./test 9.20s user 0.00s system 100% cpu 9.190 total
Second, accuracy.
1e8 eval pts from 0 to 6
maxdiff (absolute): 2.2204460492503131e-16
occuring at point where libm erf is correctly rounded, this is not.
Illustration of superior rounding of this function:
arg : 0.83999999999999997
erf : 0.76514271145499457
boost : 0.76514271145499446
real : 0.76514271145499446
i.e libm is actually incorrectly rounded. Note that this is clear from:
https://github.com/JuliaLang/openlibm/blob/master/src/s_erf.c (the Sun
implementation used by both BSD and GNU libm's), where only 1 ulp is
guaranteed.
Reasons it is not easy/worthwhile to create a "correctly rounded"
variant of this function (i.e 0.5ulp):
1. Upstream libm's don't do it anyway, so we can't guarantee this unless
we force this implementation on all platforms. This is not easy, as the
linker would complain unless measures are taken.
2. Nothing in FFmpeg cares or can care about such things, due to the
above and FFmpeg's nature.
3. Creating a correctly rounded function will in practice need some use of long
double/fma. long double, although C89/C90, unfortunately has problems on
ppc. This needs fixing of toolchain flags/configure. In any case this
will be slower for miniscule gain.
Reviewed-by: James Almer <jamrial@gmail.com>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
Here it is mostly a cosmetic change, but there might be benefits in that
there are no compat hacks for lround, while there are for lrint.
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
lrint avoids an implicit cast, and is not slower on non-broken libm's. Thus this
represents a Pareto improvement.
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
lrint is faster here on -ftree-vectorize with GCC. This is likely simply
an artifact of GCC's rather terrible auto-vectorizer, since as per the
instruction set manuals cvtsd2si and cvttsd2si (or their vector equivalents)
have identical cycle timings.
Anyway, regardless of above, lrint is superior to round accuracy wise.
Safety guaranteed as long int has at least 32 bits.
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
Otherwise the too small buffer is directly used in the frame, causing
segmentation faults, when trying to use the frame.
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
