[FFmpeg-devel] [PATCH] normal PRNG using ziggurat method

Michael Niedermayer michaelni
Tue Sep 9 04:29:41 CEST 2008

On Mon, Sep 08, 2008 at 08:05:34PM -0400, Justin Ruggles wrote:
> Hi,
> This is a patch to add a PRNG which generates numbers with standard
> normal distribution.  It uses the ziggurat method, which is quite fast
> compared to other methods.
> I was working on another implementation based on the original paper,
> which had sample code in it that I was using as a starting point.  Then
> I noticed the teeny tiny print at the bottom of the journal's download
> page which states that the code is under GPL... :(  I found another
> implementation which was based on the paper without using the
> accompanying code and is under a BSD-style license.  I trimmed it down,
> cleaned-up it up, and adapted it for FFmpeg.

> I need this for spectral extension processing in the E-AC-3 decoder.
> The spec requires that the generated noise which is blended with
> translated coeffs have "zero-mean, unity variance".

is "zero-mean, unity variance" everything the spec requires or is there
Because any signal (like the output of any PRNG) can be scaled and translated
to have that, there would be no need for normal distributed PRNG.


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Breaking DRM is a little like attempting to break through a door even
though the window is wide open and the only thing in the house is a bunch
of things you dont want and which you would get tomorrow for free anyway
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