chore: import upstream snapshot with attribution

paddle/phi/kernels/cpu/flip_kernel.cc

@@ -0,0 +1,80 @@
+// Copyright (c) 2022 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/flip_kernel.h"
+
+#include <bitset>
+
+#include "paddle/phi/backends/cpu/cpu_context.h"
+#include "paddle/phi/core/kernel_registry.h"
+
+namespace phi {
+
+constexpr size_t dim_bitset_size = 64;
+
+template <typename T, typename Context>
+void FlipKernel(const Context& dev_ctx,
+                const DenseTensor& x,
+                const std::vector<int>& axis,
+                DenseTensor* out) {
+  auto x_dims = x.dims();
+  const int total_dims = x_dims.size();
+  std::bitset<dim_bitset_size> dim_bitset;
+  for (auto& item : axis) {
+    auto dim = item;
+    if (item < 0) {
+      dim += total_dims;
+    }
+    dim_bitset[dim] = true;
+  }
+  auto x_strides = common::stride(x_dims);
+  auto numel = x.numel();
+  const T* x_data = x.data<T>();
+  T* out_data = dev_ctx.template Alloc<T>(out);
+  if (out->numel() == 0) {
+    return;
+  }
+#ifdef PADDLE_WITH_MKLML
+#pragma omp parallel for
+#endif
+  for (int64_t i = 0; i < numel; ++i) {
+    int64_t cur_indices = i;
+    int64_t rem = 0;
+    int64_t dst_offset = 0;
+
+    for (int d = 0; d < total_dims; ++d) {
+      int64_t temp = cur_indices;
+      cur_indices = cur_indices / x_strides[d];
+      rem = temp - cur_indices * x_strides[d];
+      dst_offset += dim_bitset[d] ? (x_dims[d] - 1 - cur_indices) * x_strides[d]
+                                  : cur_indices * x_strides[d];
+      cur_indices = rem;
+    }
+    out_data[i] = x_data[dst_offset];
+  }
+}
+
+}  // namespace phi
+
+PD_REGISTER_KERNEL(flip,
+                   CPU,
+                   ALL_LAYOUT,
+                   phi::FlipKernel,
+                   float,
+                   double,
+                   int32_t,
+                   int64_t,
+                   bool,
+                   phi::complex64,
+                   phi::complex128) {}