Function rand_getThreadSharedRandomSeed

quest/src/core/randomiser.cpp:175–212

unsigned rand_getThreadSharedRandomSeed(bool distinctPerNode) {

    // (callable by multiple nodes, but NOT by multiple threads!)

    // this function produces a seed which can be subsequently
    // used by many threads (each perturbing their seed via their
    // thread rank) to generate random amplitudes in parallel.
    // The dispatched seed is informed by the mainGenerator,
    // such that the user's API seeding determines both all
    // measurement outcomes and state amps, whilst retaining
    // independence amps for each subsequent random state

    // a single uniform seed suffices to seed local random amp generation
    unsigned maxSeed = std::numeric_limits<unsigned>::max();
    std::uniform_int_distribution<unsigned> distrib(0, maxSeed); // ~[0 .. max]

    // if we want the same seed on every node, advance all generators
    if (!distinctPerNode)
        return distrib(mainGenerator);

    // otherwise, if we wish for distinct per-node seeds (e.g. a
    // Qureg is distributed in a distributed environment)...
    unsigned mySeed = 0;
    int myRank = comm_getRank();
    int numNodes = comm_getNumNodes();

    // then we must advance all generators #ranks times...
    for (int rank=0; rank<numNodes; rank++) {

        unsigned globalSeed = distrib(mainGenerator);

        // but keep a distinct seed per-node
        if (rank == myRank)
            mySeed = globalSeed;
    }

    return mySeed;
}


std::mt19937_64 rand_getThreadPrivateGenerator(unsigned sharedSeed, int threadId) {