On Sat, Mar 12, 2016 at 08:58:41AM -0500, Ganesh Ajjanagadde wrote: > Code taken from the Julia project, licensed under MIT: > https://github.com/JuliaLang/julia/blob/master/base/random.jl, in turn > derived from: "The Ziggurat Method for generating random variables" - > Marsaglia and Tsang. > > Paper and reference code: http://www.jstatsoft.org/v05/i08/. This is > well known to be the fastest method empirically for generating normal random > variables for a fixed PRNG source. > > Note that there are a large number of implementations with > various tunings, this was one of the simpler ones and also has a friendly > license. > > This results in ~ 3x speedup of random number generation: > old: > 15090 decicycles in av_bmg_get, 1 runs, 0 skips > 13140 decicycles in av_bmg_get, 2 runs, 0 skips > 10117 decicycles in av_bmg_get, 4 runs, 0 skips > [...] > 2133 decicycles in av_bmg_get, 524268 runs, 20 skips=60.4x > 2134 decicycles in av_bmg_get, 1048531 runs, 45 skips=61.3x > 2135 decicycles in av_bmg_get, 2097061 runs, 91 skips=61.9x > > new: > 7650 decicycles in av_gaussian_get, 1 runs, 0 skips > 5490 decicycles in av_gaussian_get, 2 runs, 0 skips > 3982 decicycles in av_gaussian_get, 4 runs, 0 skips > [...] > 812 decicycles in av_gaussian_get, 524281 runs, 7 skips > 813 decicycles in av_gaussian_get, 1048563 runs, 13 skips > 813 decicycles in av_gaussian_get, 2097131 runs, 21 skips > > and accordingly a ~2% speedup in aac encoding (-march=native, Haswell, clang): > > old: > ffmpeg -f lavfi -i anoisesrc -t 300 -y sin_new.aac 5.30s user 0.02s system > 99% cpu 5.322 total > new: > ffmpeg -f lavfi -i anoisesrc -t 300 -y sin_new.aac 5.16s user 0.03s system > 99% cpu 5.198 total > > Function added as av_gaussian_get with documentation, minor bumped. > [...]
> +static inline double ziggurat(AVLFG *lfg)
> +{
> + while (1) {
> + uint64_t r = (((uint64_t)av_lfg_get(lfg) << 32) + av_lfg_get(lfg)) &
> 0x000fffffffffffff;
the order of Function evaluations is undefined here i think
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
I know you won't believe me, but the highest form of Human Excellence is
to question oneself and others. -- Socrates
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