Subject: Re: [Boost-users] [random] Problems generating pseudorandom 64-bit ints across multiple computers
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2009-02-24 22:28:49
AMDG
James Madison wrote:
> I am currently developing a distributed application where many clients
> need to generate unique 64-bit random numbers which will be used as
> keys. I am having problems getting boost to do this. For my first
> attempt, I tried something like the following:
>
> boost::mt19937 RandomNumberGenerator::s_algorithm;
>
> boost::uniform_int<unsigned long long>
> RandomNumberGenerator::s_range(
> std::numeric_limits<unsigned long long>::min(),
> std::numeric_limits<unsigned long long>::max());
>
> boost::variate_generator<boost::mt19937&,
> boost::uniform_int<unsigned long long> >
>
> RandomNumberGenerator::s_rng(RandomNumberGenerator::s_algorithm,
> RandomNumberGenerator::s_range);
>
> I had two issues though:
>
> 1. Is this really giving me random 64 bit numbers, or is it just
> generating 32-bit numbers and then doing bit expansion?
mt19937 generates 32 bit integers. uniform_int combines multiple
invocations
of the underlying PRNG if necessary.
> 2. The values always started with the same number.
>
> Trying to find a fix for #2, I though of using a hashed GUID as a
> seed. The problem is I noticed the seed value takes a 32 bit int,
> which essentially means a 1/2^32 chance of the first value colliding
> even if chosen completely randomly, which is unacceptable for my
> application.
There is also seed functions which takes a pair of iterators.
In Christ,
Steven Watanabe