chore: import upstream snapshot with attribution

paddle/phi/kernels/cpu/i0_kernel.cc

@@ -0,0 +1,41 @@
+/* Copyright (c) 2023 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/i0_kernel.h"
+
+#include "paddle/phi/backends/cpu/cpu_context.h"
+#include "paddle/phi/core/kernel_registry.h"
+#include "paddle/phi/kernels/funcs/for_range.h"
+#include "paddle/phi/kernels/impl/bessel_kernel_impl.h"
+
+namespace phi {
+
+template <typename T, typename Context>
+void I0Kernel(const Context& dev_ctx, const DenseTensor& x, DenseTensor* out) {
+  if (out && out->numel() == 0) {
+    dev_ctx.template Alloc<T>(out);
+    return;
+  }
+  const int64_t size = x.numel();
+  const T* x_data = x.data<T>();
+  T* out_data = dev_ctx.template Alloc<T>(out);
+
+  funcs::ForRange<Context> for_range(dev_ctx, size);
+  I0Functor<T> functor(x_data, out_data, size);
+  for_range(functor);
+}
+
+}  // namespace phi
+
+PD_REGISTER_KERNEL(i0, CPU, ALL_LAYOUT, phi::I0Kernel, float, double) {}