
/* Portions copyright (c) 2006-2013 Stanford University and Simbios.
 * Contributors: Pande Group
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject
 * to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS, CONTRIBUTORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
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 */

#ifndef OPENMM_CPU_NONBONDED_FORCE_VEC4_H__
#define OPENMM_CPU_NONBONDED_FORCE_VEC4_H__

#include "CpuNonbondedForce.h"
// ---------------------------------------------------------------------------------------

namespace OpenMM {

class CpuNonbondedForceVec4 : public CpuNonbondedForce {
public:
      /**---------------------------------------------------------------------------------------
      
         Constructor
      
         --------------------------------------------------------------------------------------- */

       CpuNonbondedForceVec4();

protected:
      /**---------------------------------------------------------------------------------------
      
         Calculate all the interactions for one atom block.
      
         @param blockIndex       the index of the atom block
         @param forces           force array (forces added)
         @param totalEnergy      total energy
            
         --------------------------------------------------------------------------------------- */
          
      void calculateBlockIxn(int blockIndex, float* forces, double* totalEnergy, const fvec4& boxSize, const fvec4& invBoxSize);
            
      /**---------------------------------------------------------------------------------------
      
         Calculate all the interactions for one atom block.
      
         @param blockIndex       the index of the atom block
         @param forces           force array (forces added)
         @param totalEnergy      total energy
            
         --------------------------------------------------------------------------------------- */
          
      void calculateBlockEwaldIxn(int blockIndex, float* forces, double* totalEnergy, const fvec4& boxSize, const fvec4& invBoxSize);

      /**
       * Compute the displacement and squared distance between a collection of points, optionally using
       * periodic boundary conditions.
       */
      void getDeltaR(const float* posI, const fvec4& x, const fvec4& y, const fvec4& z, fvec4& dx, fvec4& dy, fvec4& dz, fvec4& r2, bool periodic, const fvec4& boxSize, const fvec4& invBoxSize) const;

      /**
       * Compute a fast approximation to erfc(x).
       */
      static fvec4 erfcApprox(const fvec4& x);
      
      /**
       * Evaluate the scale factor used with Ewald and PME: erfc(alpha*r) + 2*alpha*r*exp(-alpha*alpha*r*r)/sqrt(PI)
       */
      fvec4 ewaldScaleFunction(const fvec4& x);
};

} // namespace OpenMM

// ---------------------------------------------------------------------------------------

#endif // OPENMM_CPU_NONBONDED_FORCE_VEC4_H__
