[FFmpeg-devel] [PATCHv3 1/3] lavu/rand: add 64 bit random number generator

Derek Buitenhuis derek.buitenhuis at gmail.com
Tue Mar 15 15:29:10 CET 2016

On 3/15/2016 4:46 AM, Ganesh Ajjanagadde wrote:
> Concretely, it is nearly as fast as av_lfg_get (which only returns 32 bits),
> and has a much smaller cache (128 bits). Thus, the timings should also
> be more stable.
> This is needed because av_lfg_get<<32 | av_lfg_get is far slower, and
> likely less random as measured by BigCrush - most LFG's perform
> quite poorly on the BigCrush suite:
> http://www6.tw.freebsd.org/distfiles/testu01.pdf.
> In particular, FFmpeg's seems to be Ran055 in the paper, see pg31.

This doesn't explain how it benefits our uses of PRNGs. We are a set of multimedia
libraries, not a general utilities library. Most of our use is for noise generation
or unit tests, neither of which benefits much/at all from this. For encrypted streams,
we pass in keys via options (e.g. MP4 CENC), mostly.

- Derek

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