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

Ganesh Ajjanagadde gajjanag at gmail.com
Wed Mar 16 00:21:31 CET 2016

On Tue, Mar 15, 2016 at 10:59 AM, Derek Buitenhuis
<derek.buitenhuis at gmail.com> wrote:
> On 3/15/2016 2:56 PM, Ronald S. Bultje wrote:
>> Might be related to aacenc? But yes, we need to know overall speed gain of
>> some useful end user feature before/after this.
> [13:42] <@atomnuker> well, AAC just requires the random numbers to be only somewhat random

This is extremely vague. For instance, why do you even use Gaussians
in that case? There are far cheaper distributions, e.g a uniform even
for floating point is super cheap given an integer RNG.

On the other hand, if I guess by this that you still want Gaussians,
just not necessarily very good quality ones, I am happy to drop
AVRAND64 and simply use av_lfg_get, e.g by av_lfg_get << 32 |

> [13:43] <@atomnuker> you could probably replace the random numbers with just a static table of somewhat random numbers

That would be a pretty large table, of course dependent on at what
point you are willing to cycle back through old entries.

> [13:43] <@atomnuker> and that probably won't really change much in terms of the output quality
> [13:43] <@atomnuker> though an integer RNG might be useful for some things I have in mind
> [13:44] <@Daemon404> we do have one. but it is not 64bit
> [13:44] <@atomnuker> yeah, a 32 bit one would be enough

> - Derek
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