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#ifndef GMX_EWALD_PME_GPU_UTILS_CLH
#define GMX_EWALD_PME_GPU_UTILS_CLH

/*! \internal \file
 * \brief This file defines the small PME OpenCL inline device functions.
 * This closely mirrors pme-gpu-utils.h (which is used in CUDA and unit tests), except with no templates.
 * Instead of templated parameters this file expects following defines during compilation:
 * - order - PME interpolation order;
 * - atomsPerWarp - number of atoms processed by a warp (fixed for spread and gather kernels to be the same);
 * - c_usePadding and c_skipNeutralAtoms - same as in pme-gpu-constants.h.
 *
 * \author Aleksei Iupinov <a.yupinov@gmail.com>
 * \ingroup module_ewald
 */

/*! \internal \brief
 * Gets a base of the unique index to an element in a spline parameter buffer (theta/dtheta),
 * which is laid out for GPU spread/gather kernels. The base only corresponds to the atom index within the execution block.
 * Feed the result into getSplineParamIndex() to get a full index.
 * TODO: it's likely that both parameters can be just replaced with a single atom index, as they are derived from it.
 * Do that, verifying that the generated code is not bloated, and/or revise the spline indexing scheme.
 * Removing warp dependency would also be nice (and would probably coincide with removing atomsPerWarp).
 *
 * \param[in] warpIndex        Warp index wrt the block.
 * \param[in] atomWarpIndex    Atom index wrt the warp (from 0 to atomsPerWarp - 1).
 *
 * \returns Index into theta or dtheta array using GPU layout.
 */
inline int getSplineParamIndexBase(int warpIndex, int atomWarpIndex)
{
    assert((atomWarpIndex >= 0) && (atomWarpIndex < atomsPerWarp));
    const int dimIndex    = 0;
    const int splineIndex = 0;
    // The zeroes are here to preserve the full index formula for reference
    return (((splineIndex + order * warpIndex) * DIM + dimIndex) * atomsPerWarp + atomWarpIndex);
}

/*! \internal \brief
 * Gets a unique index to an element in a spline parameter buffer (theta/dtheta),
 * which is laid out for GPU spread/gather kernels. The index is wrt to the execution block,
 * in range(0, atomsPerBlock * order * DIM).
 * This function consumes result of getSplineParamIndexBase() and adjusts it for \p dimIndex and \p splineIndex.
 *
 * \param[in] paramIndexBase   Must be result of getSplineParamIndexBase().
 * \param[in] dimIndex         Dimension index (from 0 to 2)
 * \param[in] splineIndex      Spline contribution index (from 0 to \p order - 1)
 * \param[in] order            PME order
 * \param[in] atomsPerWarp     Number of atoms processed by a warp
 *
 * \returns Index into theta or dtheta array using GPU layout.
 */
inline int getSplineParamIndex(int paramIndexBase, int dimIndex, int splineIndex)
{
    assert((dimIndex >= XX) && (dimIndex < DIM));
    assert((splineIndex >= 0) && (splineIndex < order));
    return (paramIndexBase + (splineIndex * DIM + dimIndex) * atomsPerWarp);
}

/*! \brief
 * A function for checking the global atom data indices against the atom data array sizes.
 *
 * \param[in] atomDataIndexGlobal  The atom data index.
 * \param[in] nAtomData            The atom data array element count.
 * \returns                        Non-0 if index is within bounds (or PME data padding is enabled), 0 otherwise.
 *
 * This is called from the spline_and_spread and gather PME kernels.
 * The goal is to isolate the global range checks, and allow avoiding them with c_usePadding being true.
 */
inline int pme_gpu_check_atom_data_index(const size_t atomDataIndex, const size_t nAtomData)
{
    return c_usePadding ? 1 : (atomDataIndex < nAtomData);
}

/*! \brief
 * A function for optionally skipping neutral charges, depending on c_skipNeutralAtoms.
 *
 * \param[in] coefficient     The atom charge/coefficient.
 * \returns                   Non-0 if atom should be processed, 0 otherwise.
 */
inline int pme_gpu_check_atom_charge(const float coefficient)
{
    return c_skipNeutralAtoms ? (coefficient != 0.0f) : 1;
}

#endif
