/*******************************************************************************
 * Copyright (c) 2015-2018 Skymind, Inc.
 *
 * 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 raver119@gmail.com
//

#include <ops/declarable/helpers/hashcode.h>
#include <execution/Threads.h>

namespace nd4j {
    namespace ops {
        namespace helpers {
            template <typename T>
            static void hashCode_(LaunchContext *context, NDArray &array, NDArray &result) {
                Nd4jLong blockSize = 32;
                auto length = array.lengthOf();
                int numBlocks = length / blockSize + ((length % blockSize == 0) ? 0 : 1);
                auto tempA = NDArrayFactory::create<Nd4jLong>('c', {numBlocks}, context);
                auto tempB = NDArrayFactory::create<Nd4jLong>('c', { numBlocks / blockSize + 1}, context);

                auto buffer = array.bufferAsT<T>();
                auto tempBufferA = tempA.bufferAsT<Nd4jLong>();
                auto tempBufferB = tempB.bufferAsT<Nd4jLong>();

                // default buffer is the first one, because it might be the last one in case of small arrays (< blockSize)
                auto tempBuffer = tempBufferA;
                auto tempResult = tempBufferB;

                // we divide array into 32 element chunks, and store intermediate results once
                auto func = PRAGMA_THREADS_FOR {
                    for (auto b = start; b < stop; b++) {
                        auto blockBuffer = buffer + b * numBlocks;

                        Nd4jLong r = 1;
                        for (Nd4jLong e = 0; e < blockSize && e + (b * numBlocks) < length; e++) {
                            auto v = longBytes<T>(blockBuffer[e]);
                            r = 31 * r + v;
                        }

                        tempBuffer[b] = r;
                    }
                };
                samediff::Threads::parallel_tad(func, 0, numBlocks);

                // we replace pointer with intermediate one, and repeat only one chunk left
                int iterationCount = 0;
                while (numBlocks > 1) {
                    int lastLength = numBlocks;
                    numBlocks = lastLength / blockSize + ((lastLength % blockSize == 0) ? 0 : 1);


                    auto func2 = PRAGMA_THREADS_FOR {
                        for (auto b = start; b < stop; b++) {
                            auto blockBuffer = tempBuffer + b * numBlocks;

                            Nd4jLong r = 1;
                            for (Nd4jLong e = 0; e < blockSize && e + (b * numBlocks) < lastLength; e++) {
                                auto v = longBytes<T>(blockBuffer[e]);
                                r = 31 * r + v;
                            }

                            tempResult[b] = r;
                        }
                    };
                    samediff::Threads::parallel_tad(func2, 0, numBlocks);


                    iterationCount++;
                    // swapping buffers
                    if (iterationCount % 2 == 0) {
                        tempBuffer = tempBufferA;
                        tempResult = tempBufferB;
                    } else {
                        tempBuffer = tempBufferB;
                        tempResult = tempBufferA;
                    }
                }

                if (length <= blockSize)
                    result.p(0, tempBufferA[0]);
                else
                    result.p(0, tempResult[0]);
            }


            void hashCode(LaunchContext *context, NDArray &array, NDArray &result) {
                BUILD_SINGLE_SELECTOR(array.dataType(), hashCode_, (context, array, result), LIBND4J_TYPES);
            }
        }
    }
}