text: /*******************************************************************************
   * Copyright (c) 2019-2020 Konduit K.K.
   *
   * This program and the accompanying materials are made available under the
   * terms of the Apache License, Version 2.0 which is available at
   * https://www.apache.org/licenses/LICENSE-2.0.
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
   * License for the specific language governing permissions and limitations
   * under the License.
   *
   * SPDX-License-Identifier: Apache-2.0
   ******************************************************************************/
  
  //
  // @author Oleh Semeniv (oleg.semeniv@gmail.com)
  //
  
  #include <ops/declarable/helpers/updatersHelpers.h>
  #include <execution/Threads.h>
  #include <math/platformmath.h>
  #include <math/templatemath.h>
  
  namespace sd {
  namespace ops {
  namespace helpers {
  
  //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
  template <typename T>
  static void nesterovsUpdater_(const NDArray& gradient, const NDArray& initState, NDArray& update, NDArray& stateV, const double dLr, const double dMomentum) {
  
      const T* grad = gradient.bufferAsT<T>();
      const T* init = initState.bufferAsT<T>();
  
      T* up = update.bufferAsT<T>();
      T* st = stateV.bufferAsT<T>();
  
      const T lr = static_cast<T>(dLr);
      const T momentum = static_cast<T>(dMomentum);
      const T momentumT = (-momentum - 1);
  
      bool bEws1 = 1 == gradient.ews() && 1 == update.ews() && 1 == stateV.ews() && 1 == initState.ews();
      bool bSameOrdering = gradient.ordering() == update.ordering() && update.ordering() == stateV.ordering() && stateV.ordering() == initState.ordering();
  
      if (bEws1 && bSameOrdering) {
              
              auto func = PRAGMA_THREADS_FOR{
                   for (auto i = start; i < stop; i++) {
                       T prevState = momentum * init[i];
                       st[i] = prevState - lr * grad[i];
                       up[i] = prevState + momentumT * st[i];
                   }
              };
  
             samediff::Threads::parallel_for(func, 0, gradient.lengthOf(), 1);
             return;
      }
      
      bool bXZsame = shape::haveSameShapeAndStrides(gradient.getShapeInfo(), update.getShapeInfo());
      bool bXInSame = shape::haveSameShapeAndStrides(gradient.getShapeInfo(), initState.getShapeInfo());
      bool bXStSame = shape::haveSameShapeAndStrides(gradient.getShapeInfo(), stateV.getShapeInfo());
  
      auto func = PRAGMA_THREADS_FOR{
  
          int coords[MAX_RANK];
          for (auto i = start; i < stop; i++) {
              shape::index2coordsCPU(start, i, gradient.getShapeInfo(), coords);
              const auto xOffset =  shape::getOffset(gradient.getShapeInfo(), coords);
              const auto zOffset = bXZsame ? xOffset : shape::getOffset(update.getShapeInfo(), coords);
              const auto initOffset = bXInSame ? xOffset : shape::getOffset(initState.getShapeInfo(), coords);
              const auto stOffset = bXStSame ? xOffset : shape::getOffset(stateV.getShapeInfo(), coords);
              
              T prevState = momentum * init[initOffset];
              st[stOffset] = prevState - lr * grad[xOffset];
              up[zOffset] = prevState + momentumT * st[stOffset];
          }
      };
  
      samediff::Threads::parallel_for(func, 0, gradient.lengthOf(), 1);
      return;
  }
  
  void updaterNesterovs(sd::LaunchContext* context, const NDArray& gradient, const NDArray& initState, NDArray& update, NDArray& stateV, const double dLr, const double dMomentum) {
      BUILD_SINGLE_SELECTOR(gradient.dataType(), nesterovsUpdater_, (gradient, initState, update, stateV, dLr, dMomentum), FLOAT_TYPES);
  }
  
  }
  }
  }
  