Re: [Boost-users] [random] Problems generating pseudorandom 64-bit ints across multiple computers

Subject: Re: [Boost-users] [random] Problems generating pseudorandom 64-bit ints across multiple computers
From: James Madison (jmadisondev_at_[hidden])
Date: 2009-02-27 11:15:56

Thanks for the reply, I tried implementing your suggestion of using a pair
of iterators, but I think that I might be misinterpreting the source, and
that it is still only using a 32-bit seed.

>From looking at the source, the seed appears to be stored as the variable
"i", which is of type int.  The seed method using two iterators does a ton
of mangling over the range, and assigned i to the result.

Am I misreading the source here, or no matter what I do, am I stuck with a
32 bit seed?

If so, is there a more suitable method to do what I am trying to
accomplish?  I really need the seed to be (at least) 64 bits.

On Tue, Feb 24, 2009 at 9:28 PM, Steven Watanabe <watanabesj_at_[hidden]>wrote:

> 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
>
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