src/gromacs/nbnxm/boundingboxes.h

   1 /*
   2  * This file is part of the GROMACS molecular simulation package.
   3  *
   4  * Copyright (c) 2019,2020, by the GROMACS development team, led by
   5  * Mark Abraham, David van der Spoel, Berk Hess, and Erik Lindahl,
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  35
  36 /*! \file
  37  * \internal
  38  *
  39  * \brief Declares constants and helper functions used when handling
  40  * bounding boxes for clusters of particles.
  41  *
  42  * \author Berk Hess <hess@kth.se>
  43  * \ingroup module_nbnxm
  44  */
  45
  46 #ifndef GMX_NBNXM_BOUNDINGBOXES_H
  47 #define GMX_NBNXM_BOUNDINGBOXES_H
  48
  49 #include "gromacs/simd/simd.h"
  50
  51 namespace Nbnxm
  52 {
  53
  54 /*! \brief The number of bounds along one dimension of a bounding box */
  55 static constexpr int c_numBoundingBoxBounds1D = 2;
  56
  57 } // namespace Nbnxm
  58
  59 #ifndef DOXYGEN
  60
  61 /*! \brief Bounding box calculations are (currently) always in single precision, so
  62  * we only need to check for single precision support here.
  63  * This uses less (cache-)memory and SIMD is faster, at least on x86.
  64  */
  65 #    if GMX_SIMD4_HAVE_FLOAT
  66 #        define NBNXN_SEARCH_BB_SIMD4 1
  67 #    else
  68 #        define NBNXN_SEARCH_BB_SIMD4 0
  69 #    endif
  70
  71
  72 #    if NBNXN_SEARCH_BB_SIMD4
  73 /* Always use 4-wide SIMD for bounding box calculations */
  74
  75 #        if !GMX_DOUBLE
  76 /* Single precision BBs + coordinates, we can also load coordinates with SIMD */
  77 #            define NBNXN_SEARCH_SIMD4_FLOAT_X_BB 1
  78 #        else
  79 #            define NBNXN_SEARCH_SIMD4_FLOAT_X_BB 0
  80 #        endif
  81
  82 /* Store bounding boxes corners as quadruplets: xxxxyyyyzzzz
  83  *
  84  * The packed bounding box coordinate stride is always set to 4.
  85  * With AVX we could use 8, but that turns out not to be faster.
  86  */
  87 #        define NBNXN_BBXXXX 1
  88
  89 //! The number of bounding boxes in a pack, also the size of a pack along one dimension
  90 static constexpr int c_packedBoundingBoxesDimSize = GMX_SIMD4_WIDTH;
  91
  92 //! Total number of corners (floats) in a pack of bounding boxes
  93 static constexpr int c_packedBoundingBoxesSize =
  94         c_packedBoundingBoxesDimSize * DIM * Nbnxm::c_numBoundingBoxBounds1D;
  95
  96 //! Returns the starting index of the bounding box pack that contains the given cluster
  97 static constexpr inline int packedBoundingBoxesIndex(int clusterIndex)
  98 {
  99     return (clusterIndex / c_packedBoundingBoxesDimSize) * c_packedBoundingBoxesSize;
 100 }
 101
 102 #    else /* NBNXN_SEARCH_BB_SIMD4 */
 103
 104 #        define NBNXN_SEARCH_SIMD4_FLOAT_X_BB 0
 105 #        define NBNXN_BBXXXX 0
 106
 107 #    endif /* NBNXN_SEARCH_BB_SIMD4 */
 108
 109 #endif // !DOXYGEN
 110
 111 #endif