backend_omp.hpp

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//============================================================================
// vSMC/include/vsmc/smp/backend_omp.hpp
//----------------------------------------------------------------------------
//                         vSMC: Scalable Monte Carlo
//----------------------------------------------------------------------------
// Copyright (c) 2013-2016, Yan Zhou
// All rights reserved.
//
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// modification, are permitted provided that the following conditions are met:
//
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//   this list of conditions and the following disclaimer.
//
//   Redistributions in binary form must reproduce the above copyright notice,
//   this list of conditions and the following disclaimer in the documentation
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//============================================================================

#ifndef VSMC_SMP_BACKEND_OMP_HPP
#define VSMC_SMP_BACKEND_OMP_HPP

#include <vsmc/smp/backend_base.hpp>
#include <omp.h>

namespace vsmc
{

namespace internal
{

template <typename IntType>
inline void backend_omp_range(IntType N, IntType &begin, IntType &end)
{
    const IntType np = static_cast<IntType>(::omp_get_num_threads());
    const IntType id = static_cast<IntType>(::omp_get_thread_num());
    const IntType m = N / np;
    const IntType r = N % np;
    const IntType n = m + (id < r ? 1 : 0);
    begin = id < r ? n * id : (n + 1) * r + n * (id - r);
    end = begin + n;
}

} // namespace vsmc::internal

template <typename T, typename Derived>
class SamplerEvalSMP<T, Derived, BackendOMP>
    : public SamplerEvalBase<T, Derived>
{
    public:
    std::size_t operator()(std::size_t iter, Particle<T> &particle)
    {
        using size_type = typename Particle<T>::size_type;

        this->eval_pre(iter, particle);
        std::size_t accept = 0;
        Particle<T> *pptr = &particle;
#pragma omp parallel default(none) shared(accept) firstprivate(pptr, iter)
        {
            size_type begin = 0;
            size_type end = 0;
            internal::backend_omp_range(pptr->size(), begin, end);
            std::size_t acc = this->eval_range(iter, pptr->range(begin, end));
#pragma omp atomic
            accept += acc;
        }
        this->eval_post(iter, particle);

        return accept;
    }

    protected:
    VSMC_DEFINE_SMP_BACKEND_SPECIAL(OMP, SamplerEval)
}; // class SamplerEvalSMP

template <typename T, typename Derived>
class MonitorEvalSMP<T, Derived, BackendOMP>
    : public MonitorEvalBase<T, Derived>
{
    public:
    void operator()(
        std::size_t iter, std::size_t dim, Particle<T> &particle, double *r)
    {
        using size_type = typename Particle<T>::size_type;

        this->eval_pre(iter, particle);
        Particle<T> *pptr = &particle;
#pragma omp parallel default(none) firstprivate(pptr, iter, dim, r)
        {
            size_type begin = 0;
            size_type end = 0;
            internal::backend_omp_range(pptr->size(), begin, end);
            this->eval_range(iter, dim, pptr->range(begin, end),
                r + static_cast<std::size_t>(begin) * dim);
        }
        this->eval_post(iter, particle);
    }

    protected:
    VSMC_DEFINE_SMP_BACKEND_SPECIAL(OMP, MonitorEval)
}; // class MonitorEvalSMP

template <typename T, typename Derived>
using SamplerEvalOMP = SamplerEvalSMP<T, Derived, BackendOMP>;

template <typename T, typename Derived>
using MonitorEvalOMP = MonitorEvalSMP<T, Derived, BackendOMP>;

} // namespace vsmc

#endif // VSMC_SMP_BACKEND_OMP_HPP