Re: [boost] [random] new threefry random engine

Subject: Re: [boost] [random] new threefry random engine
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2014-04-19 19:39:35

AMDG

On 04/19/2014 04:35 PM, Thijs van den Berg wrote:
> What’s your view on limiting the round to <=20 for the template

I still don't like it.  If all else fails, you can use the
optimized version for rounds <= 20, and the slow version
for rounds > 20.

> and providing only the 20 round as a typedef?
> 

I'd favor providing both.  There are plenty of inferior algorithms
in Boost.Random.  I would anticipate that anyone who wants to
use an algorithm other than mt19937 would have some idea of
the tradeoffs.

> I have addressed most other points you’ve mentioned, but the performance issue of a generic rounds version has failed me.
> 

In theory it could be optimized.  What compiler and
optimization settings are you using?  In particular,
are you using -funroll-loops (GCC)?  The version
you show unrolls the loop 4x.  What if you
unroll 8x and kill the constant arrays?  What
about 20x and eliminate the % 5 in the key addition?
Or 40x and eliminate both?

In Christ,
Steven Watanabe