/*
 *  Copyright (C) 2004-2021 Edward F. Valeev
 *
 *  This file is part of Libint.
 *
 *  Libint is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU Lesser General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  Libint is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public License
 *  along with Libint.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

#ifndef _libint2_src_lib_libint_genericgaussderivimpl_h_
#define _libint2_src_lib_libint_genericgaussderivimpl_h_

#include <GenericGaussDeriv.h>

namespace libint2 {

  /** builds ( ... d a / d r_dir ... )
      src0 = ( ... a+1 ... )
      src1 = ( ... a-1 ... )
   **/
  template <int L,       //!< the angular momentum of this shell (i.e. the shell being differentiated)
            bool vectorize>
  void
  GenericGaussDeriv<L,vectorize>::compute(const Libint_t* inteval,
                        LIBINT2_REALTYPE* target,
                        const LIBINT2_REALTYPE* src0,
                        const LIBINT2_REALTYPE* src1,
                        unsigned int highdim, //!< number of functions more significant than this shell
                        unsigned int lowdim, //!<  number of functions less significant than this shell
                        unsigned int dir, //!< Cartesian direction of the derivative (0, 1, 2)
                        const LIBINT2_REALTYPE (&two_alpha)[LIBINT2_MAX_VECLEN] //!< The gaussian exponent of the function being differentiated)
                       )
    {

      const unsigned int veclen = vectorize ? inteval->veclen : 1;
      const unsigned int lveclen = lowdim * veclen;

      const unsigned int N = INT_NCART(L);
      const unsigned int Np1 = INT_NCART(L+1);
      const unsigned int Nm1 = L > 0 ? INT_NCART(L-1) : 0;  // L == 0 case will not use Nm1

      for(unsigned int h=0, target_idx=0; h<highdim; ++h) {

        const unsigned int hNp1 = h * Np1;
        const unsigned int hNm1 = h * Nm1;

        int ax, ay, az;
        FOR_CART(ax, ay, az, L)

          int a[3]; a[0] = ax;  a[1] = ay;  a[2] = az;

          // d |a) / dRi = 2 alpha a+1_i
          ++a[dir];
          const unsigned int iap1 = INT_CARTINDEX(L+1,a[0],a[1]);
          const unsigned int ap1_offset = (hNp1 + iap1) * lveclen;
          const LIBINT2_REALTYPE* src0_ptr = src0 + ap1_offset;
          --a[dir];

          const bool have_am1 = (a[dir] > 0);
          // d |a) / dRi -=  a_i a-1_i
          unsigned int iam1;
          unsigned int am1_offset;
          const LIBINT2_REALTYPE* src1_ptr;
          if (have_am1) {
            --a[dir];
            iam1 = INT_CARTINDEX(L-1,a[0],a[1]);
            am1_offset = (hNm1 + iam1) * lveclen;
            src1_ptr = src1 + am1_offset;
            ++a[dir];
          }
          LIBINT2_REALTYPE adir_real = LIBINT2_REALTYPE(a[dir]);

          if (have_am1)
          for(unsigned int l = 0, lv=0; l < lowdim; ++l) {
            for(unsigned int v=0; v<veclen; ++v, ++lv, ++target_idx) {
              target[target_idx] = two_alpha[v] * src0_ptr[lv] - adir_real * src1_ptr[lv];
            }
          }
          else
          for(unsigned int l = 0, lv=0; l < lowdim; ++l) {
            for(unsigned int v=0; v<veclen; ++v, ++lv, ++target_idx) {
              target[target_idx] = two_alpha[v] * src0_ptr[lv];
            }
          }

#if LIBINT2_FLOP_COUNT
          inteval->nflops[0] += (have_am1 ? 3 : 1) * lveclen;
#endif

        END_FOR_CART // end of loop over a

      }
    }

}; // namespace libint2

#endif // header guard

