I am having trouble with rand_r. I have a simulation that generates millions of random numbers. I have noticed that at a certain point in time, these numbers are no longer uniform. What could be the problem?
What i do: i create an instance of a generator and give it is own seed.
mainRGen= new nativeRandRUni(idumSeed_g);
here is the class/object def:
class nativeRandRUni {
public:
unsigned seed;
nativeRandRUni(unsigned sd){ seed= sd; }
float genP() { return (rand_r(&seed))/float(RAND_MAX); } // [0,1]
int genI(int R) { return (rand_r(&seed) % R); } // [0,R-1]
};
numbers are simply generated by:
newIntNumber= mainRGen->genI(desired_max);
newFloatNumber= mainRGen->genP();
the simulations have the problem described above. I know this is happening cause i have checked the distribution of the generated numbers after the point in time that a signature is shown in the results (see this, top image, http://ubuntuone.com/0tbfidZaXfGNTfiVr3x7DR)
also, if i print the seed at t-1 and t, being t the time point of the signature, i can see the seed changing by an order of magnitude from value 263069042 to 1069048066
if i run the code with a different seed, the problem is always present but at different time points
Also, if i use rand() instead of my object, all goes well... i DO need the object cause sometimes i used threads. The example above does not have threads.
i am really lost here, any clues?
EDIT - EDIT
it can be reproducible by looping enough times, problem is that, like i said, it takes millions of iterations for the problem to arise. For seed -158342163 i get it at generation t=134065568. One can check numbers generated before (uniform) and after (not uniform). I get the same problem if i change the seed manually at given t's, see (*) in code. Something i also do not expect to happen?
#include <tr1/random>
#include <fstream>
#include <sstream>
#include <iostream>
using std::ofstream;
using std::cout;
using std::endl;
class nativeRandRUni {
public:
unsigned seed;
long count;
nativeRandRUni(unsigned sd){ seed= sd; count=0; }
float genP() { count++; return (rand_r(&seed))/float(RAND_MAX); } // [0,1]
int genI(int R) { count++; return (rand_r(&seed) % R); } // [0,R-1]
};
int main(int argc, char *argv[]){
long timePointOfProblem= 134065568;
nativeRandRUni* mainRGen= new nativeRandRUni(-158342163);
int rr;
//ofstream* fout_metaAux= new ofstream();
//fout_metaAux->open("random.numbers");
for(int i=0; i< timePointOfProblem; i++){
rr= mainRGen->genI(1009200);
//(*fout_metaAux) << rr << endl;
//if(i%1000==0) mainRGen->seed= 111111; //(*) FORCE
}
//fout_metaAux->close();
}