[WIP] Histogram CPU

Signed-off-by: Piotr Rak <prak@nvidia.com>

Author: prak-nv

dali/operators/generic/reduce/axes_helper.h

@@ -0,0 +1,60 @@
+// Copyright (c) 2020-2021, NVIDIA CORPORATION & AFFILIATES. 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 DALI_OPERATORS_GENERIC_REDUCE_AXIS_HELPER_H__
+#define DALI_OPERATORS_GENERIC_REDUCE_AXIS_HELPER_H__
+
+#include <vector>
+
+#include "dali/pipeline/operator/operator.h"
+
+namespace dali {
+namespace detail {
+
+class AxesHelper {
+ public:
+  explicit inline AxesHelper(const OpSpec &spec) {
+    has_axes_arg_ = spec.TryGetRepeatedArgument(axes_, "axes");
+    has_axis_names_arg_ = spec.TryGetArgument(axis_names_, "axis_names");
+    has_empty_axes_arg_ =
+        (has_axes_arg_ && axes_.empty()) || (has_axis_names_arg_ && axis_names_.empty());
+
+    DALI_ENFORCE(!has_axes_arg_ || !has_axis_names_arg_,
+                 "Arguments `axes` and `axis_names` are mutually exclusive");
+  }
+
+  void PrepareAxes(const TensorLayout &layout, int sample_dim) {
+    if (has_axis_names_arg_) {
+      axes_ = GetDimIndices(layout, axis_names_).to_vector();
+      return;
+    }
+
+    if (!has_axes_arg_) {
+      axes_.resize(sample_dim);
+      std::iota(axes_.begin(), axes_.end(), 0);
+    }
+  }
+
+  bool has_axes_arg_;
+  bool has_axis_names_arg_;
+  bool has_empty_axes_arg_;
+  std::vector<int> axes_;
+  TensorLayout axis_names_;
+};
+
+}  // namespace detail
+}  // namespace dali
+
+#endif  // DALI_OPERATORS_GENERIC_REDUCE_AXIS_HELPER_H__