CODEWITHSUNDEEP
cvisual-studio
bmanga
bmanga

Reputation: 140

Why does this poisson distribution implementation return 0 on msvc

I am curious why the following implementation always return 0 using the visual studio compiler, but it works fine when compiled with gcc and clang

int poissrand(double lambda){
  int k=0;
  double L=exp(-lambda), p=1;
  do {
    ++k;
    p *= rand()/(double)INT_MAX;
  } while (p > L);
  return --k;
}

Examples here (vc) and here (gcc)

Upvotes: 1

Views: 69

Answers (1)

Weather Vane
Weather Vane

Reputation: 34575

In MSVC the range of rand() is different. In all versions it is specified by RAND_MAX in stdlib.h.

If the value you multiply p by is supposed to be in the range 0..1 then please try

p *= (double)rand() / RAND_MAX;

Upvotes: 4

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