[FFmpeg-devel] [PATCH] avutil/tests/lfg.c: added proper normality test

[Thomas Turner]

On Wed, Feb 22, 2017 at 2:16 PM, Michael Niedermayer <michael at niedermayer.cc
> wrote:

> oops forgot to reply to all, this one went only to thomas by mistake
>
> On Tue, Feb 21, 2017 at 08:12:57PM -0800, Thomas Turner wrote:
> >
> >
> > On 02/17/2017 02:15 PM, Michael Niedermayer wrote:
> > > On Thu, Feb 16, 2017 at 08:29:38PM -0800, Thomas Turner wrote:
> > >> The Chen-Shapiro(CS) test was used to test normality for
> > >> Lagged Fibonacci PRNG.
> > >>
> > >> Normality Hypothesis Test:
> > >>
> > >> The null hypothesis formally tests if the population
> > >> the sample represents is normally-distributed. For
> > >> CS, when the normality hypothesis is True, the
> > >> distribution of QH will have a mean close to 1.
> > >>
> > >> Information on CS can be found here:
> > >>
> > >> http://www.stata-journal.com/sjpdf.html?articlenum=st0264
> > >> http://www.originlab.com/doc/Origin-Help/NormalityTest-Algorithm
> > >>
> > >> Signed-off-by: Thomas Turner <thomastdt at googlemail.com>
> > >> ---
> > >>  libavutil/tests/lfg.c    |  170 ++++++--
> > >>  tests/fate/libavutil.mak |    4 +
> > >>  tests/ref/fate/lfg       | 1007 ++++++++++++++++++++++++++++++
> ++++++++++++++++
> > >>  3 files changed, 1157 insertions(+), 24 deletions(-)
> > >>  create mode 100644 tests/ref/fate/lfg
> > >
> > > works on x86_64 linux but fails on x86_32
> >
> > What if we force gcc compiler to use IEEE 754 floating-point
> semantics...Will adding the following gcc compilation flags to ffmpeg
> configuration allow the test to pass? : -msse2 -mfpmath=sse
>
> there is no gurantee that the hardware this runs on supports sse
> nor that the compiler is gcc
>
> C has a somewhat loose definition of floating point operations,
> that allows C compilers to perform more optimizations and run on more
> hardware. There isnt much that can be done about this, short of not
> using floating point
>
> But why does it not work with default options?
>
x86_32 machine produces a negative overflow for double precision value. But
unable to figure out precisely why. my guesstimation would be because of
the difference in floating point arithmetic.

> or is that unknown ?
> did you succeed in reproduring the issue ?
>
trying to compile 32bit on my 64bit machine with:

./configure --enable-debug=3 --cc='cc -m32'
but i get the following error:

cc -m32 is unable to create an executable file.
If cc -m32 is a cross-compiler, use the --enable-cross-compile option.
Only do this if you know what cross compiling means.
C compiler test failed.


> [...]
>
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> There will always be a question for which you do not know the correct
> answer.
>
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