+1
On Feb 7, 2014, at 5:23 PM, Joshua Ladd <josh...@mellanox.com>
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: josh...@mellanox.com
> Cell: +1 (865) 258 - 8898
>
>
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--
Jeff Squyres
jsquy...@cisco.com
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