birthday_spacings_test.hpp

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//============================================================================
// MCKL/include/mckl/random/birthday_spacings_test.hpp
//----------------------------------------------------------------------------
// MCKL: Monte Carlo Kernel Library
//----------------------------------------------------------------------------
// Copyright (c) 2013-2018, Yan Zhou
// All rights reserved.
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#ifndef MCKL_RANDOM_BIRTHDAY_SPACINGS_TEST_HPP
#define MCKL_RANDOM_BIRTHDAY_SPACINGS_TEST_HPP

#include <mckl/random/internal/common.hpp>
#include <mckl/random/poisson_test.hpp>

namespace mckl {

template <std::size_t D, std::size_t T>
class BirthdaySpacingsTest : public PoissonTest<BirthdaySpacingsTest<D, T>>
{
    static_assert(D > 1, "**BirthdaySpacingsTest** used with D less than two");

    static_assert(T > 0, "**BirthdaySpacingsTest** used with T equal to zero");

  public:
    BirthdaySpacingsTest(std::size_t n) : n_(n)
    {
        mean_ = std::exp(3 * std::log(static_cast<double>(n)) -
            std::log(static_cast<double>(K_)) - 2 * const_ln_2<double>());
    }

    MCKL_DEFINE_RANDOM_TEST_OPERATOR(std::size_t)

    template <typename RNGType, typename U01DistributionType>
    std::size_t operator()(RNGType &rng, U01DistributionType &u01)
    {
        using result_type = typename U01DistributionType::result_type;

        const std::size_t k = internal::BufferSize<result_type, T>::value;
        const std::size_t m = n_ / k;
        const std::size_t l = n_ % k;
        Vector<result_type> r(k * T);
        Vector<std::size_t> spacings(n_);
        std::size_t *s = spacings.data();
        for (std::size_t i = 0; i != m; ++i, s += k) {
            generate(rng, u01, k, r.data(), s);
        }
        generate(rng, u01, l, r.data(), s);

        std::size_t d0 = spacings.front();
        std::sort(spacings.begin(), spacings.end());
        for (std::size_t i = 0; i != n_ - 1; ++i) {
            spacings[i] = spacings[i + 1] - spacings[i];
        }
        spacings.back() = K_ - spacings.back() + d0;
        std::sort(spacings.begin(), spacings.end());
        std::size_t e = 0;
        for (std::size_t i = 0; i != n_ - 1; ++i) {
            if (spacings[i] == spacings[i + 1]) {
                ++e;
            }
        }

        return e;
    }

    double mean() const { return mean_; }

  private:
    static constexpr std::size_t K_ = internal::Pow<std::size_t, D, T>::value;

    std::size_t n_;
    double mean_;

    template <typename RNGType, typename U01DistributionType>
    void generate(RNGType &rng, U01DistributionType &u01, std::size_t n,
        typename U01DistributionType::result_type *r, std::size_t *s)
    {
        rand(rng, u01, n * T, r);
        mul(n * T, static_cast<typename U01DistributionType::result_type>(D),
            r, r);
        for (std::size_t i = 0; i != n; ++i, r += T) {
            s[i] = internal::serial_index<D, T>(r);
        }
    }
}; // class BirthdaySpacingsTest

} // namespace mckl

#endif // MCKL_RANDOM_BIRTHDAY_SPACINGS_TEST_HPP