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

Subject: Re: [boost] [random] new threefry random engine
From: John Salmon (john_at_[hidden])
Date: 2014-05-02 07:39:48

On Fri, May 2, 2014 at 1:26 AM, Steven Watanabe <watanabesj_at_[hidden]>wrote:

> AMDG
>
> On 04/27/2014 05:39 AM, Mathias Gaunard wrote:
> >
> > With a single, stateless generator, everything is much simpler. One
> > seed, one generator, completely reproducible results regardless of
> > scheduling. The interface i want to have is this:
> >
> > #pragma omp for
> > for(int i=0; i<n; ++i)
> > {
> >   out[i] = in[i] * random_value(i);
> > }
> >
>
> The proposed RandomFunction doesn't quite work this
> way.  It produces random numbers in blocks.  (For
> instance, the threefry engine that started this thread,
> uses a 256-bit block size.)
>

Yes.  But with C++11 initializer lists, random_value is a one-liner:

unsigned random_value(unsigned i){
    return Threefry<2, unsigned>()({i})[0];
}

Without initializer lists, you would need another line for a  declaration
of a domain_type.

Alternatively, you may prefer to let a distribution do the rescaling for
you:

Threefry<2,unsigned> prf;
uniform_real_distribution<float> zero_one(0., 1.);
#omp
for(int i=0; i<n; ++i)
{
     out[i] = in[i]*zero_one( counter_based_urng(prf, {i}) );
}

John Salmon

>