Random Perl Content

Ruud H.G. van Tol rvtol at isolution.nl
Sun May 19 01:26:00 BST 2013

On 18/05/2013 23:29, Abigail wrote:
> On Sat, May 18, 2013 at 01:53:33PM -0700, Randy J. Ray wrote:

>> (It's a pun, see, because I'm going to be asking about random number
>> generators... get it? Get it...?)
>> (Short, TL;DR summary: I'm looking for a pRNG that can have multiple
>> instances at once that don't affect each others' stream of numbers. Does
>> Math::Random::MT meet that criteria?)
>> I considered posing this to Perlmonks, but I just don't frequent that
>> site like I used to. And there are enough Large Perl Brains on this list
>> that I should get as good an answer, if not better.
>> I am looking for a pRNG (pseudo-Random Number Generator) module. But I
>> have an unusual requirement-- I need to be able to instantiate multiple
>> *independent* generators, that can take seeds for the sake of
>> reproducible results. Let me explain...
>> My current (paying) job is writing frameworks for automated QA of my
>> company's software (mainly the operating system that runs our storage
>> servers). We are working on a new approach to how we structure some of
>> our tests, and that happens to involve the potential of using some
>> randomization to select different paths over a directed graph. But, this
>> being QA-oriented, even if something runs with a degree of randomness to
>> it, it needs to be reproducible at a later time. So, no problem, just
>> create a seed for srand() and log that seed, and also provide users a
>> way to specify a seed at the start. Then you can just re-use the seed
>> and reproduce your results. Right? Well, not exactly...
>> Other libraries I use, developed by other teams within our company,
>> might also have some randomization in them (like generating random names
>> for disk volumes, randomizing data generation for traffic testing,
>> etc.). Not to mention that we use no small number of CPAN modules, some
>> of which might use rand() as well. I could seed Perl's RNG with a
>> specific seed, but if that run has to try twice to generate a unique
>> file name, instead of one or thrice, that will affect the random numbers
>> *my* code gets.
>> So my thought was that sure there's a RNG module out there that is OO,
>> and encapsulates the seed and all other internal elements of the
>> generation process. One that I can instantiate multiple instances of,
>> and have them generate streams of random numbers that are independent of
>> each other. The closest I've found is Math::Random::MT, which implements
>> the Mersenne Twister pRNG. But I can't immediately tell from the docs
>> whether the object instances it creates are truly independent of each
>> other or not.
>> So, is this something anyone else here has dealt with? Are there modules
>> I just haven't stumbled upon yet, that would do this for me? Any help
>> greatly appreciated, as always.
> I'm not aware of any Perl modules that provide this functionality,
> but on my Linux box, there are the C functions erand48, nrand48
> and jrand48. It would be fairly trivial to call those functions
> using a few simple lines of XS.

Math::Rand48 looks promising.


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