// **************************************************************************
//                               coul_long_cs.cu
//                             -------------------
//                           Trung Nguyen (Northwestern)
//
//  Device code for acceleration of the coul/long/cs pair style
//
// __________________________________________________________________________
//    This file is part of the LAMMPS Accelerator Library (LAMMPS_AL)
// __________________________________________________________________________
//
//    begin                : June 2018
//    email                : ndactrung@gmail.com
// ***************************************************************************

#if defined(NV_KERNEL) || defined(USE_HIP)

#include "lal_aux_fun1.h"
#ifndef _DOUBLE_DOUBLE
_texture( pos_tex,float4);
_texture( q_tex,float);
#else
_texture_2d( pos_tex,int4);
_texture( q_tex,int2);
#endif

#else
#define pos_tex x_
#define q_tex q_
#endif

// Note: EWALD_P is different from that in lal_preprocessor.h
//       acctyp is needed for these parameters
#define CS_EWALD_P (acctyp)9.95473818e-1
#define B0        (acctyp)-0.1335096380159268
#define B1        (acctyp)-2.57839507e-1
#define B2        (acctyp)-1.37203639e-1
#define B3        (acctyp)-8.88822059e-3
#define B4        (acctyp)-5.80844129e-3
#define B5        (acctyp)1.14652755e-1

#define EPSILON (acctyp)(1.0e-20)
#define EPS_EWALD (acctyp)(1.0e-6)
#define EPS_EWALD_SQR (acctyp)(1.0e-12)

__kernel void k_coul_long_cs(const __global numtyp4 *restrict x_,
                          const __global numtyp *restrict scale,
                          const int lj_types,
                          const __global numtyp *restrict sp_cl_in,
                          const __global int *dev_nbor,
                          const __global int *dev_packed,
                          __global acctyp4 *restrict ans,
                          __global acctyp *restrict engv,
                          const int eflag, const int vflag, const int inum,
                          const int nbor_pitch,
                          const __global numtyp *restrict q_,
                          const numtyp cut_coulsq, const numtyp qqrd2e,
                          const numtyp g_ewald, const int t_per_atom) {
  int tid, ii, offset;
  atom_info(t_per_atom,ii,tid,offset);

  __local numtyp sp_cl[4];
  int n_stride;
  local_allocate_store_charge();

  sp_cl[0]=sp_cl_in[0];
  sp_cl[1]=sp_cl_in[1];
  sp_cl[2]=sp_cl_in[2];
  sp_cl[3]=sp_cl_in[3];

  acctyp4 f;
  f.x=(acctyp)0; f.y=(acctyp)0; f.z=(acctyp)0;
  acctyp e_coul, virial[6];
  if (EVFLAG) {
    e_coul=(acctyp)0;
    for (int i=0; i<6; i++) virial[i]=(acctyp)0;
  }

  if (ii<inum) {
    int nbor, nbor_end;
    int i, numj;
    nbor_info(dev_nbor,dev_packed,nbor_pitch,t_per_atom,ii,offset,i,numj,
              n_stride,nbor_end,nbor);

    numtyp4 ix; fetch4(ix,i,pos_tex); //x_[i];
    int itype=ix.w;
    numtyp qtmp; fetch(qtmp,i,q_tex);

    for ( ; nbor<nbor_end; nbor+=n_stride) {
      int j=dev_packed[nbor];

      numtyp factor_coul;
      factor_coul = sp_cl[sbmask(j)];
      j &= NEIGHMASK;

      numtyp4 jx; fetch4(jx,j,pos_tex); //x_[j];
      int jtype=jx.w;

      // Compute r12
      numtyp delx = ix.x-jx.x;
      numtyp dely = ix.y-jx.y;
      numtyp delz = ix.z-jx.z;
      numtyp rsq = delx*delx+dely*dely+delz*delz;

      int mtype=itype*lj_types+jtype;
      if (rsq < cut_coulsq) {
        rsq += EPSILON; // Add Epsilon for case: r = 0; Interaction must be removed by special bond;

        numtyp force,prefactor,_erfc;
        numtyp r2inv = ucl_recip(rsq);
        numtyp r = ucl_rsqrt(r2inv);
        fetch(prefactor,j,q_tex);
        prefactor *= qqrd2e * scale[mtype] * qtmp;
        if (factor_coul<(numtyp)1.0) {
          numtyp grij = g_ewald * (r+EPS_EWALD);
          numtyp expm2 = ucl_exp(-grij*grij);
          acctyp t = ucl_recip((numtyp)1.0 + CS_EWALD_P*grij);
          numtyp u = (numtyp)1.0 - t;
          _erfc = t * ((numtyp)1.0 + u*(B0+u*(B1+u*(B2+u*(B3+u*(B4+u*B5)))))) * expm2;
          prefactor /= (r+EPS_EWALD);
          force = prefactor * (_erfc + EWALD_F*grij*expm2 - ((numtyp)1.0-factor_coul));
          // Additionally r2inv needs to be accordingly modified since the later
          // scaling of the overall force shall be consistent
          r2inv = ucl_recip(rsq + EPS_EWALD_SQR);
          force *= r2inv;
        } else {
          numtyp grij = g_ewald * r;
          numtyp expm2 = ucl_exp(-grij*grij);
          acctyp t = ucl_recip((numtyp)1.0 + CS_EWALD_P*grij);
          numtyp u = (numtyp)1.0 - t;
          _erfc = t * ((numtyp)1.0 + u*(B0+u*(B1+u*(B2+u*(B3+u*(B4+u*B5)))))) * expm2;
          prefactor /= r;
          force = prefactor*(_erfc + EWALD_F*grij*expm2);
          force *= r2inv;
        }

        f.x+=delx*force;
        f.y+=dely*force;
        f.z+=delz*force;

        if (EVFLAG && eflag) {
          numtyp e = prefactor*_erfc;
          if (factor_coul<(numtyp)1.0) e -= ((numtyp)1.0-factor_coul)*prefactor;
          e_coul += e;
        }
        if (EVFLAG && vflag) {
          virial[0] += delx*delx*force;
          virial[1] += dely*dely*force;
          virial[2] += delz*delz*force;
          virial[3] += delx*dely*force;
          virial[4] += delx*delz*force;
          virial[5] += dely*delz*force;
        }
      }

    } // for nbor
  } // if ii
  acctyp energy;
  if (EVFLAG) energy=(acctyp)0.0;
  store_answers_q(f,energy,e_coul,virial,ii,inum,tid,t_per_atom,offset,eflag,
                  vflag,ans,engv);
}

__kernel void k_coul_long_cs_fast(const __global numtyp4 *restrict x_,
                               const __global numtyp *restrict scale_in,
                               const __global numtyp *restrict sp_cl_in,
                               const __global int *dev_nbor,
                               const __global int *dev_packed,
                               __global acctyp4 *restrict ans,
                               __global acctyp *restrict engv,
                               const int eflag, const int vflag, const int inum,
                               const int nbor_pitch,
                               const __global numtyp *restrict q_,
                               const numtyp cut_coulsq, const numtyp qqrd2e,
                               const numtyp g_ewald, const int t_per_atom) {
  int tid, ii, offset;
  atom_info(t_per_atom,ii,tid,offset);

  __local numtyp scale[MAX_SHARED_TYPES*MAX_SHARED_TYPES];
  __local numtyp sp_cl[4];
  int n_stride;
  local_allocate_store_charge();

  if (tid<4)
    sp_cl[tid]=sp_cl_in[tid];
  if (tid<MAX_SHARED_TYPES*MAX_SHARED_TYPES)
    scale[tid]=scale_in[tid];

  acctyp4 f;
  f.x=(acctyp)0; f.y=(acctyp)0; f.z=(acctyp)0;
  acctyp e_coul, virial[6];
  if (EVFLAG) {
    e_coul=(acctyp)0;
    for (int i=0; i<6; i++) virial[i]=(acctyp)0;
  }

  __syncthreads();

  if (ii<inum) {
    int nbor, nbor_end;
    int i, numj;
    nbor_info(dev_nbor,dev_packed,nbor_pitch,t_per_atom,ii,offset,i,numj,
              n_stride,nbor_end,nbor);

    numtyp4 ix; fetch4(ix,i,pos_tex); //x_[i];
    numtyp qtmp; fetch(qtmp,i,q_tex);
    int iw=ix.w;
    int itype=fast_mul((int)MAX_SHARED_TYPES,iw);

    for ( ; nbor<nbor_end; nbor+=n_stride) {
      int j=dev_packed[nbor];

      numtyp factor_coul;
      factor_coul = sp_cl[sbmask(j)];
      j &= NEIGHMASK;

      numtyp4 jx; fetch4(jx,j,pos_tex); //x_[j];
      int mtype=itype+jx.w;

      // Compute r12
      numtyp delx = ix.x-jx.x;
      numtyp dely = ix.y-jx.y;
      numtyp delz = ix.z-jx.z;
      numtyp rsq = delx*delx+dely*dely+delz*delz;

      if (rsq < cut_coulsq) {
        rsq += EPSILON; // Add Epsilon for case: r = 0; Interaction must be removed by special bond;

        numtyp force,prefactor,_erfc;
        numtyp r2inv = ucl_recip(rsq);
        numtyp r = ucl_rsqrt(r2inv);
        fetch(prefactor,j,q_tex);
        prefactor *= qqrd2e * scale[mtype] * qtmp;
        if (factor_coul<(numtyp)1.0) {
          numtyp grij = g_ewald * (r+EPS_EWALD);
          numtyp expm2 = ucl_exp(-grij*grij);
          acctyp t = ucl_recip((numtyp)1.0 + CS_EWALD_P*grij);
          numtyp u = (numtyp)1.0 - t;
          _erfc = t * ((numtyp)1.0 + u*(B0+u*(B1+u*(B2+u*(B3+u*(B4+u*B5)))))) * expm2;
          prefactor /= (r+EPS_EWALD);
          force = prefactor * (_erfc + EWALD_F*grij*expm2 - ((numtyp)1.0-factor_coul));
          // Additionally r2inv needs to be accordingly modified since the later
          // scaling of the overall force shall be consistent
          r2inv = ucl_recip(rsq + EPS_EWALD_SQR);
        } else {
          numtyp grij = g_ewald * r;
          numtyp expm2 = ucl_exp(-grij*grij);
          acctyp t = ucl_recip((numtyp)1.0 + CS_EWALD_P*grij);
          numtyp u = (numtyp)1.0 - t;
          _erfc = t * ((numtyp)1.0 + u*(B0+u*(B1+u*(B2+u*(B3+u*(B4+u*B5)))))) * expm2;
          prefactor /= r;
          force = prefactor * (_erfc + EWALD_F*grij*expm2);
        }

        force *= r2inv;

        f.x+=delx*force;
        f.y+=dely*force;
        f.z+=delz*force;

        if (EVFLAG && eflag) {
          numtyp e = prefactor*_erfc;
          if (factor_coul<(numtyp)1.0) e -= ((numtyp)1.0-factor_coul)*prefactor;
          e_coul += e;
        }
        if (EVFLAG && vflag) {
          virial[0] += delx*delx*force;
          virial[1] += dely*dely*force;
          virial[2] += delz*delz*force;
          virial[3] += delx*dely*force;
          virial[4] += delx*delz*force;
          virial[5] += dely*delz*force;
        }
      }

    } // for nbor
  } // if ii
  acctyp energy;
  if (EVFLAG) energy=(acctyp)0.0;
  store_answers_q(f,energy,e_coul,virial,ii,inum,tid,t_per_atom,offset,eflag,
                  vflag,ans,engv);
}