[Boost-users] [random] fast uniform integer random distribution

From: frederic.bron_at_[hidden]
Date: 2007-11-21 10:37:21

Hi,

I face a speed problem. I need a uniform distribution of integers between 0 and N, N around 10^11.
I tried 2 methods with very high speed efficiency difference (time x8). The 1st one is based on uniform_smallint (the slowest method) and the 2nd one is based on a real distribution casted to an
integer.
Is there a problem with the 2nd method which is much quicker?

Fred

common code:

typedef boost::mt19937 base_generator_type;
base_generator_type generator;
generator.seed(static_cast<unsigned int>(std::time(0))) ;

method 1 (using uniform_smallint):

boost::uniform_smallint<uint32_t> uni_dist((uint32_t)0, (uint32_t)10000000000);
boost::variate_generator<base_generator_type*, boost::uniform_smallint<uint32_t> > uni(&generator, uni_dist);
for (unsigned long k=0 ; k<100000000UL; ++k) uni() ;

method 2 (using uniform_real and casting):

boost::uniform_real<double> uni_dist(0., 100000000001.);
boost::variate_generator<base_generator_type*, boost::uniform_real<double> > uni(&generator, uni_dist);
for (unsigned long k=0 ; k<100000000UL; ++k) (uint32_t)uni() ;

F. Bron
___________________________________
Frédéric Bron (frederic.bron_at_[hidden])
Unité ALT, Alcan CRV, BP 27, 38341 Voreppe
téléphone : [phone]
télécopie : [phone]

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