[Issue 6594] Xorshift as default generator

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=6594



--- Comment #3 from Joseph Rushton Wakeling <joseph.wakeling at webdrake.net> 2013-07-05 08:37:38 PDT ---
(In reply to comment #2)
> The performance penalty most probably comes from passing it (by value) to
> algorithms or whatnot.

If you're passing it by value, you have bigger problems than slowdown ... :-)

> I know for a fact this *will* cause significant slowdown. I observed this while
> implementing a Lagged Fibonacci PRNG, whose size varies a lot. The bigger
> flavors of the PRNG would make the runtime grind to a halt, while the biggest
> versions simply stack overflowed.
> 
> ----
> All this to say, I think it is not the algorithm of mersenne itself that is
> slow, but rather the range implementation. Until this is fixed, we *may* want
> to change the default.

Fully agree that the real solution here is to change the RNGs to reference
types.  I don't think switching default to Xorshift is a good idea, though,
even as a short term method.  Apart from any other consideration, Issue #10550
should give us pause on that idea.

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