[Bug-gsl] initialisation of random number generator on 64bit machine

[Vito Trianni]

Hello,
I noticed the following behaviour when initialising the random number 
generator on a 64bit machine. Basically, on a 64 bit machine, the 
unsigned long int probably provokes an overflow in the gsl_rng_set() 
function, so that the initialisation of the seed in some way fails, and 
I got always identical numbers despite different seeds. Here is part of 
the code that made the overflow:

unsigned long int un_seed = GetSomeSeed(); // this function returns a 
random number in [0,ULONG_MAX]

gsl_rng_env_setup();
T = gsl_rng_default;
gsl_rng* r = gsl_rng_alloc ( T );
gsl_rng_set ( r, un_seed );    // here probably the overflow

int value = gsl_rng_uniform_int(r, 1000); // retruns always the same 
number, despite different seeds


For the time being, I bypassed the problem by limiting the seed to 
UINT_MAX, which does not produces overflows on the 64bit machines.
I hope this report is useful....


regards,
Vito



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Vito Trianni, Ph.D.                  vito.trianni@(no_spam)istc.cnr.it
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