/* Copyright 2019 The TensorFlow Authors. All Rights Reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://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.
==============================================================================*/

#ifndef TENSORFLOW_CORE_KERNELS_STATEFUL_RANDOM_OPS_CPU_GPU_H_
#define TENSORFLOW_CORE_KERNELS_STATEFUL_RANDOM_OPS_CPU_GPU_H_

#include "tensorflow/core/framework/resource_var.h"
#include "tensorflow/core/kernels/stateful_random_ops.h"

namespace tensorflow {

// The following 5 functions are made templates to avoid duplicate symbols when
// linking.

// The following 2 functions use the contract "lower 32 bits for the first
// uint32, higher 32 bits for the second". Note that this is endian-neutral,
// unlike a direct memory copy `memcpy(output, &input, 8)`.
PHILOX_DEVICE_INLINE void Int64ToUint32s(int64 input, uint32* output1,
                                         uint32* output2) {
  auto u64 = static_cast<uint64>(input);
  *output1 = static_cast<uint32>(u64);
  *output2 = static_cast<uint32>(u64 >> 32);
}

PHILOX_DEVICE_INLINE int64 Uint32sToInt64(uint32 input1, uint32 input2) {
  auto u64_1 = static_cast<uint64>(input1);
  auto u64_2 = static_cast<uint64>(input2);
  return static_cast<int64>(u64_1 | (u64_2 << 32));
}

PHILOX_DEVICE_INLINE PhiloxRandom
GetPhiloxRandomFromMem(StateElementType const* ptr) {
  PhiloxRandom::ResultType counter;
  PhiloxRandom::Key key;
  Int64ToUint32s(ptr[0], &counter[0], &counter[1]);
  Int64ToUint32s(ptr[1], &counter[2], &counter[3]);
  Int64ToUint32s(ptr[2], &key[0], &key[1]);
  return PhiloxRandom(counter, key);
}

PHILOX_DEVICE_INLINE void WritePhiloxRandomToMem(PhiloxRandom const& philox,
                                                 StateElementType* ptr) {
  PhiloxRandom::ResultType const& counter = philox.counter();
  PhiloxRandom::Key const& key = philox.key();
  ptr[0] = Uint32sToInt64(counter[0], counter[1]);
  ptr[1] = Uint32sToInt64(counter[2], counter[3]);
  ptr[2] = Uint32sToInt64(key[0], key[1]);
}

PHILOX_DEVICE_INLINE void UpdateMemWithPhiloxRandom(PhiloxRandom const& philox,
                                                    int64 output_size,
                                                    StateElementType* ptr) {
  auto new_philox = philox;
  // Multiplier 256 is the same as in `FillPhiloxRandomTask`; do not change
  // it just here.
  auto delta = output_size * 256;
  new_philox.Skip(delta);  // do the actual increasing
  WritePhiloxRandomToMem(new_philox, ptr);
}

// A per-device helper function that does the actual work for
// `UpdateVariableAndFill`.
// Reason to use functor: C++ doesn't allow function-template partial
// specialization.
template <typename Device, typename Distribution>
struct UpdateVariableAndFill_Philox;

template <typename Device>
struct RngSkip_Philox;

using CPUDevice = Eigen::ThreadPoolDevice;

#if GOOGLE_CUDA

using GPUDevice = Eigen::GpuDevice;

// Declares the partially GPU-specialized functor structs.
template <typename Distribution>
struct UpdateVariableAndFill_Philox<GPUDevice, Distribution> {
  void operator()(OpKernelContext* ctx, const GPUDevice& device,
                  Distribution dist, int64 output_size, int64 alg_tag_skip,
                  ScopedUnlockUnrefVar* not_used, Tensor* state_tensor,
                  typename Distribution::ResultElementType* output_data);
};

template <>
struct RngSkip_Philox<GPUDevice> {
  void operator()(const GPUDevice& device, int64 delta, Tensor* state_tensor);
};

#endif  // GOOGLE_CUDA

}  // end namespace tensorflow

#endif  // TENSORFLOW_CORE_KERNELS_STATEFUL_RANDOM_OPS_CPU_GPU_H_
