Function bernoulli

crawl-ref/source/random.cc:423–428

Roll n_trials, return true if at least one succeeded. n_trials might be not integer. [0, 1]

// not integer.
// [0, 1]
bool bernoulli(double n_trials, double trial_prob)
{
    if (n_trials <= 0 || trial_prob <= 0)
        return false;
    return !decimal_chance(pow(1 - trial_prob, n_trials));
}

bool one_chance_in(int a_million)
{