// Copyright (c) 2021 PaddlePaddle 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.

#include "paddle/phi/kernels/dot_kernel.h"

#include "paddle/phi/backends/cpu/cpu_context.h"
#include "paddle/phi/core/kernel_registry.h"

#include "paddle/phi/kernels/full_kernel.h"

namespace phi {

template <typename T, typename Context>
void DotKernel(const Context& dev_ctx,
               const DenseTensor& x,
               const DenseTensor& y,
               DenseTensor* out) {
  if (x.numel() == 0 || y.numel() == 0) {
    // x[2, 1], y[2, 0], out[2]
    Full<T, Context>(dev_ctx, out->dims(), 0, out);
    return;
  }
  if (out->numel() <= 0) {
    return;
  }
  auto const *x_ptr = x.data<T>(), *x_ptr_ = &x_ptr[0];
  auto const *y_ptr = y.data<T>(), *y_ptr_ = &y_ptr[0];
  T* z = dev_ctx.template Alloc<T>(out);

  // Loop over the total N elements of both operands while sum-reducing every
  // B pairs along the way where B is the dimension of the least ordered axis
  auto&& d = x.dims();
  auto const N = x.numel();

  // prevent div 0
  auto const _B = d.size() == 0 ? 1 : d[d.size() - 1];
  auto const B = _B != 0 ? _B : 1;

  // initialize for N / B <= 0
  z[0] = 0;

  for (int j = 0; j < N / B; j++) {
    T ss = 0;
    for (int i = 0; i < B; i++) ss += (*x_ptr_++) * (*y_ptr_++);
    z[j] = ss;
  }
}

}  // namespace phi

PD_REGISTER_KERNEL(dot,
                   CPU,
                   ALL_LAYOUT,
                   phi::DotKernel,
                   float,
                   double,
                   int,
                   int64_t,
                   phi::complex64,
                   phi::complex128) {}