Add softmax function (#93)

* Add softmax function

* Add softmax unittest

* Add Softmax docs

* Add function directory

* Add comment for FD_VISIT_ALL_TYPES macro

csrc/fastdeploy/utils/axis_utils.h

@@ -0,0 +1,52 @@
+// 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.
+
+#pragma once
+
+namespace fastdeploy {
+
+static inline int CanonicalAxis(const int axis, const int rank) {
+  if (axis < 0) {
+    return axis + rank;
+  }
+  return axis;
+}
+
+static inline int SizeToAxis(const int axis, const std::vector<int64_t>& dims) {
+  int size = 1;
+  for (int i = 0; i < axis; i++) {
+    size *= dims[i];
+  }
+  return size;
+}
+
+static inline int SizeFromAxis(const int axis,
+                               const std::vector<int64_t>& dims) {
+  int size = 1;
+  for (int i = axis; i < dims.size(); i++) {
+    size *= dims[i];
+  }
+  return size;
+}
+
+static inline int SizeOutAxis(const int axis,
+                              const std::vector<int64_t>& dims) {
+  int size = 1;
+  for (int i = axis + 1; i < dims.size(); i++) {
+    size *= dims[i];
+  }
+  return size;
+}
+
+}  // namespace fastdeploy