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>
For systems with broken libms.
Tested with NAN, -NAN, INFINITY, -INFINITY, +/-x for regular double x and
combinations of these.
Old versions of MSVC need some UINT64_C hackery.
Reviewed-by: Ronald S. Bultje <rsbultje@gmail.com>
Reviewed-by: Hendrik Leppkes <h.leppkes@gmail.com>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
arc4random() was designed as a superior interface for system random
number generation, designed for OpenBSD and subsequently incorporated by
other BSD's, Mac OS X, and some non-standard libc's. It is thus an improvement to
use it whenever available.
As a side note, this may or may not get included in glibc, and there is
a proposal to create a posix_random family based on these ideas:
http://austingroupbugs.net/view.php?id=859.
Tested on Mac OS X.
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
* commit 'e02de9df4b218bd6e1e927b67fd4075741545688':
lavc: export Dirac parsing API used by the ogg demuxer as public
Merged-by: Hendrik Leppkes <h.leppkes@gmail.com>
Having a configure option with the same name as a MIPS ISA is confusing,
so better to remove it. This option was being used to add some
optimizations to a specific core (i6400). We will add the optimizations
just when the i6400 core has been detected, in a later patch.
Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
Having a configure option with the same name as a MIPS ISA is confusing,
so better to remove it. This option was being used to add some
optimizations to a specific core (p5600). We will add the optimizations
just when the p5600 core has been detected, in a later patch.
Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
This fixes builds with --disable-vda, which previously failed with
undefined references to CVImageBuffer* and CVPixelBuffer* functions.
Signed-off-by: Martin Storsjö <martin@martin.st>
While pr is a valid POSIX.1 command, its usage in configure
is a little borderline and is possible to replace it with
printf.
Bug-Id: 913
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
* commit 'afdff8008149515afebf9992eae84be7d76e6b1e':
configure: Clearly state that MSYS native builds are discouraged
Merged-by: Hendrik Leppkes <h.leppkes@gmail.com>
MSYS, as per cygwin, by default uses a custom posix abstraction
in the form of a "msys2.dll". Programs build that way are harder to
distribute and use.
MSYS2 provides alternate launcher scripts that provide a MINGW
environment nearly out of box.
It is known that the naive sqrt(x*x + y*y) approach for computing the
hypotenuse suffers from overflow and accuracy issues, see e.g
http://www.johndcook.com/blog/2010/06/02/whats-so-hard-about-finding-a-hypotenuse/.
This adds hypot support to FFmpeg, a C99 function.
On platforms without hypot, this patch does a reaonable workaround, that
although not as accurate as GNU libm, is readable and does not suffer
from the overflow issue. Improvements can be made separately.
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
This implementation does not support TLS listen sockets and loading
CA/Certs from files.
The Windows API does not support loading PEM certs, and would either
require a manual loader or instead be limited to loading Windows PFX
certificates
TLS listen sockets would have to be implemented quite separately, as many
of the APIs are different for server-mode (as opposed to client mode).
* commit 'a0562e531723923b632684c7b51a9dd584bf534f':
configure: Add a SONAME entry for the android target
Merged-by: Hendrik Leppkes <h.leppkes@gmail.com>
* commit '00b62968d079e63bf22028f253ac297292436ebe':
os_support: Don't try to return the service name as a string in getnameinfo
Merged-by: Hendrik Leppkes <h.leppkes@gmail.com>
* commit '567ca142952c5be57e52c149c815dfe5d6ac6d41':
configure: Add -D_CRT_NONSTDC_NO_WARNINGS when building with msvc
Merged-by: Hendrik Leppkes <h.leppkes@gmail.com>
In order to load libraries in Android they need to be unversioned.
The android target section was derived from the BSD ones, and they
that simply drop the SONAME
Android M requires to have a SONAME entry but unversioned.
Some systems may be lacking getservbyport; the previous ifdef wasn't
quite enough since it still assumed that struct servent was defined,
as pointed out by Clément Gregoire.
Simply remove the possibility to return non-numeric services in
getnameinfo; no caller of getnameinfo within libavformat
currently try to use getnameinfo for retrieving the port number without
NI_NUMERICSERV, and falling back on getservbyport may be non-threadsafe.
Signed-off-by: Martin Storsjö <martin@martin.st>
This silences warnings like this one:
libavformat/file.c(62) : warning C4996: 'read': The POSIX name for this
item is deprecated. Instead, use the ISO C++ conformant name: _read.
See online help for details.
Signed-off-by: Martin Storsjö <martin@martin.st>
