Method initialize

src/random.cpp:30–74

If parameter p.deterministic is true, we'll initialize the RNG with the seed specified in parameter p.RNGSeed, otherwise we'll initialize the RNG with a random seed. This initializes both the Marsaglia and the Jenkins algorithms. The member function operator() determines which algorithm is actually used.

// the Jenkins algorithms. The member function operator() determines
// which algorithm is actually used.
void RandomUintGenerator::initialize()
{
    if (p.deterministic) {
        // Initialize Marsaglia. Overflow wrap-around is ok. We just want
        // the four parameters to be unrelated. In the extremely unlikely
        // event that a coefficient is zero, we'll force it to an arbitrary
        // non-zero value. Each thread uses a different seed, yet
        // deterministic per-thread.
        rngx = p.RNGSeed + 123456789 + omp_get_thread_num();
        rngy = p.RNGSeed + 362436000 + omp_get_thread_num();
        rngz = p.RNGSeed + 521288629 + omp_get_thread_num();
        rngc = p.RNGSeed + 7654321 + omp_get_thread_num();
        rngx = rngx != 0 ? rngx : 123456789;
        rngy = rngy != 0 ? rngy : 123456789;
        rngz = rngz != 0 ? rngz : 123456789;
        rngc = rngc != 0 ? rngc : 123456789;

        // Initialize Jenkins determinstically per-thread:
        a = 0xf1ea5eed;
        b = c = d = p.RNGSeed + omp_get_thread_num();
        if (b == 0) {
            b = c = d + 123456789;
        }
    } else {
        // Non-deterministic initialization.
        // First we will get a random number from the built-in mt19937
        // (Mersenne twister) generator and use that to derive the
        // starting coefficients for the Marsaglia and Jenkins RNGs.
        // We'll seed mt19937 with time(), but that has a coarse
        // resolution and multiple threads might be initializing their
        // instances at nearly the same time, so we'll add the thread
        // number to uniquely seed mt19937 per-thread.
        std::mt19937 generator(time(0) + omp_get_thread_num());

        // Initialize Marsaglia, but don't let any of the values be zero:
        do { rngx = generator(); } while (rngx == 0);
        do { rngy = generator(); } while (rngy == 0);
        do { rngz = generator(); } while (rngz == 0);
        do { rngc = generator(); } while (rngc == 0);

        // Initialize Jenkins, but don't let any of the values be zero:
        a = 0xf1ea5eed;
        do { b = c = d = generator(); } while (b == 0);
    }
}


// This returns a random 32-bit integer. Neither the Marsaglia nor the Jenkins