/* -------------------------------------------------------------------------- *
 *                                   OpenMM                                   *
 * -------------------------------------------------------------------------- *
 * This is part of the OpenMM molecular simulation toolkit originating from   *
 * Simbios, the NIH National Center for Physics-Based Simulation of           *
 * Biological Structures at Stanford, funded under the NIH Roadmap for        *
 * Medical Research, grant U54 GM072970. See https://simtk.org.               *
 *                                                                            *
 * Portions copyright (c) 2008-2009 Stanford University and the Authors.      *
 * Authors: Peter Eastman, Mark Friedrichs, Chris Bruns, Mike Houston         *
 * Contributors:                                                              *
 *                                                                            *
 * 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 WITH THE SOFTWARE OR THE  *
 * USE OR OTHER DEALINGS IN THE SOFTWARE.                                     *
 * -------------------------------------------------------------------------- */

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

   This kernel calculates the linear momentum

   @param mass           stream of masses
   @param velocities     stream of velocities
   @param linearMomentum output stream of linear momentum

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

kernel void kCalculateLinearMomentum( float mass<>, float3 velocities<>, out float3 linearMomentum<> ){
   linearMomentum = mass*velocities;
}

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

   This kernel scales the linear momentum

   @param scale              scale factor
   @param linearMomentumIn   input linearMomentum
   @param linearMomentumOut  output linearMomentum

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

kernel void kScale( float scale, float3 linearMomentumIn<>, out float3 linearMomentumOut<> ){
   linearMomentumOut = scale*linearMomentumIn;
}

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

   This kernel calculates the total linear momentum via a reduction

   @param momentum       momentum
   @param linearMomentum total momentum

   Note: treating the output linearMomentum as non-stream did not compile, even though
   I found examples in Brook testing code that had that construct -- MSF 3/6/08

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

reduce void kReduceLinearMomentum( float3 momentum<>, reduce float3 linearMomentum<> ){
   linearMomentum += momentum;
}

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

   This kernel calculates the total linear momentum via a reduction

   @param atomStrWidth   atom stream width
   @param numberOfAtoms  number of atoms
   @param momentum       momentum
   @param linearMomentum total momentum

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

kernel void kSumLinearMomentum( float atomStrWidth, float numberOfAtoms, float scale, float3 momentum[][],
                                out float3 linearMomentum<> ){

   float atomCount;
   float2 atomIndex;

   atomCount      = 0.0f;
   linearMomentum = float3( 0.0f, 0.0f, 0.0f );
   atomIndex.y    =  0.0f;
   atomIndex.x    =  0.0f;

   while( atomCount < numberOfAtoms ){

      linearMomentum += momentum[atomIndex];

      atomIndex.x    += 1.0f;
      if( atomIndex.x == atomStrWidth ){
         atomIndex.x  = 0.0f; 
         atomIndex.y += 1.0f;
      }

      atomCount += 1.0f;
   } 
   linearMomentum *= scale;
}

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

   This kernel calculates the total linear momentum via a reduction

   @param momentum       momentum
   @param linearMomentum total momentum

   Note: treating the output linearMomentum as non-stream did not compile, even though
   I found examples in Brook testing code that had that construct -- MSF 3/6/08

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

reduce void kSum( float3 array<>, reduce float3 sum<> ){
   //sum += array;
   //sum += array.x + array.y + array.z;
   //sum += float3( 1.0, 1.0, 1.0 );
/*
   sum.x += 1.0;
   sum.y += 1.0;
   sum.z += 1.0;
*/
   sum += array;
   //sum += 1.0;
}

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

   This kernel subtracts the (total linear momentum)/totalMass from the velocities 

   @param linearMomentum  normalized linear momentum
   @param velocities      stream of velocities
   @param velocitiesOut   output stream of velocities

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

kernel void kRemoveLinearMomentum( float3 linearMomentum[], float3 velocities<>, out float3 velocitiesOut<> ){
   velocitiesOut = velocities - linearMomentum[0];
}