/* ----------------------------------------------------------------------
   LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
   http://lammps.sandia.gov, Sandia National Laboratories
   Steve Plimpton, sjplimp@sandia.gov

   This software is distributed under the GNU General Public License.

   See the README file in the top-level LAMMPS directory.
------------------------------------------------------------------------- */

/* ----------------------------------------------------------------------
   Contributing author: Axel Kohlmeyer (Temple U)
------------------------------------------------------------------------- */

#include "math.h"
#include "pair_nm_cut_coul_long_omp.h"
#include "atom.h"
#include "comm.h"
#include "force.h"
#include "neighbor.h"
#include "neigh_list.h"

#include "suffix.h"
using namespace LAMMPS_NS;

#define EWALD_F   1.12837917
#define EWALD_P   0.3275911
#define A1        0.254829592
#define A2       -0.284496736
#define A3        1.421413741
#define A4       -1.453152027
#define A5        1.061405429

/* ---------------------------------------------------------------------- */

PairNMCutCoulLongOMP::PairNMCutCoulLongOMP(LAMMPS *lmp) :
  PairNMCutCoulLong(lmp), ThrOMP(lmp, THR_PAIR)
{
  suffix_flag |= Suffix::OMP;
  respa_enable = 0;
}

/* ---------------------------------------------------------------------- */

void PairNMCutCoulLongOMP::compute(int eflag, int vflag)
{
  if (eflag || vflag) {
    ev_setup(eflag,vflag);
  } else evflag = vflag_fdotr = 0;

  const int nall = atom->nlocal + atom->nghost;
  const int nthreads = comm->nthreads;
  const int inum = list->inum;

#if defined(_OPENMP)
#pragma omp parallel default(none) shared(eflag,vflag)
#endif
  {
    int ifrom, ito, tid;

    loop_setup_thr(ifrom, ito, tid, inum, nthreads);
    ThrData *thr = fix->get_thr(tid);
    ev_setup_thr(eflag, vflag, nall, eatom, vatom, thr);

    if (evflag) {
      if (eflag) {
        if (force->newton_pair) eval<1,1,1>(ifrom, ito, thr);
        else eval<1,1,0>(ifrom, ito, thr);
      } else {
        if (force->newton_pair) eval<1,0,1>(ifrom, ito, thr);
        else eval<1,0,0>(ifrom, ito, thr);
      }
    } else {
      if (force->newton_pair) eval<0,0,1>(ifrom, ito, thr);
      else eval<0,0,0>(ifrom, ito, thr);
    }

    reduce_thr(this, eflag, vflag, thr);
  } // end of omp parallel region
}

/* ---------------------------------------------------------------------- */

template <int EVFLAG, int EFLAG, int NEWTON_PAIR>
void PairNMCutCoulLongOMP::eval(int iifrom, int iito, ThrData * const thr)
{
  int i,j,ii,jj,jnum,jtype,itable;
  double qtmp,xtmp,ytmp,ztmp,delx,dely,delz,evdwl,ecoul,fpair;
  double fraction,table;
  double r,rsq,rinv,r2inv,factor_coul,factor_lj;
  double forcecoul,forcenm,rminv,rninv;
  double grij,expm2,prefactor,t,erfc;
  int *ilist,*jlist,*numneigh,**firstneigh;

  evdwl = ecoul = 0.0;

  const dbl3_t * _noalias const x = (dbl3_t *) atom->x[0];
  dbl3_t * _noalias const f = (dbl3_t *) thr->get_f()[0];
  const double * _noalias const q = atom->q;
  const int * _noalias const type = atom->type;
  const int nlocal = atom->nlocal;
  const double * _noalias const special_coul = force->special_coul;
  const double * _noalias const special_lj = force->special_lj;
  const double qqrd2e = force->qqrd2e;
  double fxtmp,fytmp,fztmp;

  ilist = list->ilist;
  numneigh = list->numneigh;
  firstneigh = list->firstneigh;

  // loop over neighbors of my atoms

  for (ii = iifrom; ii < iito; ++ii) {

    const int i = ilist[ii];
    const int itype = type[i];
    const int    * _noalias const jlist = firstneigh[i];
    const double * _noalias const cutsqi = cutsq[itype];
    const double * _noalias const cut_ljsqi = cut_ljsq[itype];
    const double * _noalias const offseti = offset[itype];
    const double * _noalias const mmi = mm[itype];
    const double * _noalias const nni = nn[itype];
    const double * _noalias const nmi = nm[itype];
    const double * _noalias const e0nmi = e0nm[itype];
    const double * _noalias const r0mi = r0m[itype];
    const double * _noalias const r0ni = r0n[itype];

    qtmp = q[i];
    xtmp = x[i].x;
    ytmp = x[i].y;
    ztmp = x[i].z;
    jnum = numneigh[i];
    fxtmp=fytmp=fztmp=0.0;

    for (jj = 0; jj < jnum; jj++) {
      j = jlist[jj];
      factor_lj = special_lj[sbmask(j)];
      factor_coul = special_coul[sbmask(j)];
      j &= NEIGHMASK;

      delx = xtmp - x[j].x;
      dely = ytmp - x[j].y;
      delz = ztmp - x[j].z;
      rsq = delx*delx + dely*dely + delz*delz;
      jtype = type[j];

      if (rsq < cutsqi[jtype]) {
        r2inv = 1.0/rsq;

        if (rsq < cut_coulsq) {
          if (!ncoultablebits || rsq <= tabinnersq) {
            r = sqrt(rsq);
            grij = g_ewald * r;
            expm2 = exp(-grij*grij);
            t = 1.0 / (1.0 + EWALD_P*grij);
            erfc = t * (A1+t*(A2+t*(A3+t*(A4+t*A5)))) * expm2;
            prefactor = qqrd2e * qtmp*q[j]/r;
            forcecoul = prefactor * (erfc + EWALD_F*grij*expm2);
            if (EFLAG) ecoul = prefactor*erfc;
            if (factor_coul < 1.0) {
              forcecoul -= (1.0-factor_coul)*prefactor;
              if (EFLAG) ecoul -= (1.0-factor_coul)*prefactor;
            }
          } else {
            union_int_float_t rsq_lookup;
            rsq_lookup.f = rsq;
            itable = rsq_lookup.i & ncoulmask;
            itable >>= ncoulshiftbits;
            fraction = (rsq_lookup.f - rtable[itable]) * drtable[itable];
            table = ftable[itable] + fraction*dftable[itable];
            forcecoul = qtmp*q[j] * table;
            if (EFLAG)
              ecoul = qtmp*q[j] * (etable[itable] + fraction*detable[itable]);
            if (factor_coul < 1.0) {
              table = ctable[itable] + fraction*dctable[itable];
              prefactor = qtmp*q[j] * table;
              forcecoul -= (1.0-factor_coul)*prefactor;
              if (EFLAG) ecoul -= (1.0-factor_coul)*prefactor;
            }
          }
        } else {
            forcecoul = 0.0;
            if (EFLAG) ecoul = 0.0;
        }

        if (rsq < cut_ljsqi[jtype]) {
          r = sqrt(rsq);
          rminv = pow(r2inv,mmi[jtype]/2.0);
          rninv = pow(r2inv,nni[jtype]/2.0);
          forcenm = e0nmi[jtype]*nmi[jtype] *
            (r0ni[jtype]/pow(r,nni[jtype]) -
             r0mi[jtype]/pow(r,mmi[jtype]));
          forcenm *= factor_lj;
          if (EFLAG)
            evdwl = (e0nmi[jtype]*(mmi[jtype] *
                                   r0ni[jtype]*rninv -
                                   nni[jtype] *
                                   r0mi[jtype]*rminv) -
                     offseti[jtype]) * factor_lj;
        } else {
          forcenm = 0.0;
          if (EFLAG) evdwl = 0.0;
        }

        fpair = (forcecoul + forcenm) * r2inv;

        fxtmp += delx*fpair;
        fytmp += dely*fpair;
        fztmp += delz*fpair;
        if (NEWTON_PAIR || j < nlocal) {
          f[j].x -= delx*fpair;
          f[j].y -= dely*fpair;
          f[j].z -= delz*fpair;
        }

        if (EVFLAG) ev_tally_thr(this, i,j,nlocal,NEWTON_PAIR,
                                 evdwl,ecoul,fpair,delx,dely,delz,thr);
      }
    }
    f[i].x += fxtmp;
    f[i].y += fytmp;
    f[i].z += fztmp;
  }
}

/* ---------------------------------------------------------------------- */

  double PairNMCutCoulLongOMP::memory_usage()
  {
    double bytes = memory_usage_thr();
    bytes += PairNMCutCoulLong::memory_usage();

    return bytes;
  }
