src/gromacs/pbcutil/pbc_simd.h

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  35 /*! \libinternal \file
  36  *
  37  * \brief This file contains a definition, declaration and inline function
  38  * for SIMD accelerated PBC calculations.
  39  *
  40  * \author Berk Hess <hess@kth.se>
  41  * \inlibraryapi
  42  * \ingroup module_pbcutil
  43  */
  44
  45 #ifndef GMX_PBCUTIL_PBC_SIMD_H
  46 #define GMX_PBCUTIL_PBC_SIMD_H
  47
  48 #include "config.h"
  49
  50 #include "gromacs/pbcutil/pbc.h"
  51 #include "gromacs/simd/simd.h"
  52
  53 struct gmx_domdec_t;
  54
  55 /*! \brief Set the SIMD PBC data from a normal t_pbc struct.
  56  *
  57  * \param pbc        Type of periodic boundary,
  58  *                   NULL can be passed for then no PBC will be used.
  59  * \param pbc_simd   Pointer to aligned memory with (DIM + DIM*(DIM+1)/2)
  60  *                   GMX_SIMD_REAL_WIDTH reals describing the box vectors
  61  *                   unrolled by GMX_SIMD_REAL_WIDTH.
  62  *                   These are sorted in a slightly non-standard
  63  *                   order so that we always issue the memory loads in order
  64  *                   (to improve prefetching) in pbc_correct_dx_simd().
  65  *                   The order is inv_bzz, bzx, bzy, bzz, inv_byy, byx, byy,
  66  *                   inv_bxx, and bxx.
  67  */
  68 void set_pbc_simd(const t_pbc *pbc,
  69                   real        *pbc_simd);
  70
  71 #if GMX_SIMD_HAVE_REAL
  72
  73 /*! \brief Correct SIMD distance vector *dx,*dy,*dz for PBC using SIMD.
  74  *
  75  * For rectangular boxes all returned distance vectors are the shortest.
  76  * For triclinic boxes only distances up to half the smallest box diagonal
  77  * element are guaranteed to be the shortest. This means that distances from
  78  * 0.5/sqrt(2) times a box vector length (e.g. for a rhombic dodecahedron)
  79  * can use a more distant periodic image.
  80  * Note that this routine always does PBC arithmetic, even for dimensions
  81  * without PBC. But on modern processors the overhead of this, often called,
  82  * routine should be low. On e.g. Intel Haswell/Broadwell it takes 8 cycles.
  83  */
  84 static inline void gmx_simdcall
  85 pbc_correct_dx_simd(gmx::SimdReal         *dx,
  86                     gmx::SimdReal         *dy,
  87                     gmx::SimdReal         *dz,
  88                     const real            *pbc_simd)
  89 {
  90     using namespace gmx;
  91     SimdReal shz, shy, shx;
  92
  93     shz = round(*dz * load<SimdReal>(pbc_simd+0*GMX_SIMD_REAL_WIDTH)); // load inv_bzz
  94     *dx = *dx - shz * load<SimdReal>(pbc_simd+1*GMX_SIMD_REAL_WIDTH);  // load bzx
  95     *dy = *dy - shz * load<SimdReal>(pbc_simd+2*GMX_SIMD_REAL_WIDTH);  // load bzy
  96     *dz = *dz - shz * load<SimdReal>(pbc_simd+3*GMX_SIMD_REAL_WIDTH);  // load bzz
  97
  98     shy = round(*dy * load<SimdReal>(pbc_simd+4*GMX_SIMD_REAL_WIDTH)); // load inv_byy
  99     *dx = *dx - shy * load<SimdReal>(pbc_simd+5*GMX_SIMD_REAL_WIDTH);  // load byx
 100     *dy = *dy - shy * load<SimdReal>(pbc_simd+6*GMX_SIMD_REAL_WIDTH);  // load byy
 101
 102     shx = round(*dx * load<SimdReal>(pbc_simd+7*GMX_SIMD_REAL_WIDTH)); // load inv_bxx
 103     *dx = *dx - shx * load<SimdReal>(pbc_simd+8*GMX_SIMD_REAL_WIDTH);  // load bxx
 104
 105 }
 106
 107 /*! \brief Calculates the PBC corrected distance between SIMD coordinates.
 108  *
 109  * \param pbc_simd  SIMD formatted PBC information
 110  * \param x1        Packed coordinates of atom1, size 3*GMX_SIMD_REAL_WIDTH
 111  * \param x2        Packed coordinates of atom2, size 3*GMX_SIMD_REAL_WIDTH
 112  * \param dx        The PBC corrected distance x1 - x2
 113  *
 114  * This routine only returns the shortest distance correctd for PBC
 115  * when all atoms are in the unit-cell (aiuc).
 116  * This is the SIMD equivalent of the scalar version declared in pbc.h.
 117  */
 118 static inline void gmx_simdcall
 119 pbc_dx_aiuc(const real            *pbc_simd,
 120             const gmx::SimdReal   *x1,
 121             const gmx::SimdReal   *x2,
 122             gmx::SimdReal         *dx)
 123 {
 124     for (int d = 0; d < DIM; d++)
 125     {
 126         dx[d] = x1[d] - x2[d];
 127     }
 128     pbc_correct_dx_simd(&dx[XX], &dx[YY], &dx[ZZ], pbc_simd);
 129 }
 130
 131 #endif /* GMX_SIMD_HAVE_REAL */
 132
 133 #endif