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Subject: Re: [OMPI devel] RFC: Add an OPAL rand and srand
From: Nathan Hjelm (hjelmn_at_[hidden])
Date: 2014-02-07 17:48:42


+1.

On Fri, Feb 07, 2014 at 10:23:41PM +0000, Joshua Ladd wrote:
> What: Add an internal random number generator to OPAL.
>
>
>
> Why: OMPI uses rand and srand all over the place. Because the middleware
> is mucking with the RNG's global state, applications that use these
> library routines will not achieve reproducible results with the same seed.
>
>
>
> How: I plan to put in an additive lagged Fibonacci generator seeded with a
> Tausworthe generator that itself is seeded by the user's seed. The short
> story here is that the ALFG has a toroidal state space, i.e. it can be
> decomposed into non-overlapping cycles with maximal period. It's well
> understood how to fully enumerate these cycles when, for a length k
> register composed of m-bit words, we view this as a k X m binary matrix.
> It was proven by Marsaglia et al. that this matrix has a canonical form
> that is uniquely determined by the values k and l (the two numbers that
> (almost) completely characterize an ALFG.) So, distinct seeds are
> guaranteed to map to distinct, non-overlapping, long period streams that
> have measurably very, very low inter- and intra-stream correlations. We
> used this for large scale Monte Carlo simulations back in my PhD days.
>
>
>
> Will define a new type:
>
>
>
> struct opal_rng_buffer_t {
>
>
>
> uint32_t buff[127]; /* if people are going to pitch a fit over the size,
> we can go smaller, down to 7, but, obviously, this affects the quality of
> the streams */
>
> int tap1;
>
> int tap2;
>
>
>
> };
>
>
>
> and two functions:
>
>
>
> /* User is responsible for defining his/her own opal_rng_buffer_t
>
> * or malloc-ing and managing the resources themselves.
>
> */
>
> int opal_srand(opal_rng_buffer_t *buff, uint32_t seed);
>
>
>
> /* Returns a 32-bit pseudo random integer */
>
> uint32_t opal_rand(opal_rng_buffer_t *buff);
>
>
>
>
>
> When: Should be in by the end of February. Code is written, but
> integration and testing always takes some time.
>
>
>
>
>
>
>
> Joshua S. Ladd, PhD
>
> HPC Algorithms Engineer
>
> Mellanox Technologies
>
>
>
> Email: joshual_at_[hidden]
>
> Cell: +1 (865) 258 - 8898
>
>
>
>

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