Add softmax function (#93)

* Add softmax function

* Add softmax unittest

* Add Softmax docs

* Add function directory

* Add comment for FD_VISIT_ALL_TYPES macro

tests/function/test_softmax.cc

@@ -0,0 +1,48 @@
+// 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 <vector>
+#include "fastdeploy/core/fd_tensor.h"
+#include "fastdeploy/function/softmax.h"
+#include "glog/logging.h"
+#include "gtest/gtest.h"
+#include "gtest_utils.h"
+
+namespace fastdeploy {
+#ifdef ENABLE_FDTENSOR_FUNC
+TEST(fastdeploy, softmax) {
+  FDTensor input, output;
+  CheckShape check_shape;
+  CheckData check_data;
+  std::vector<float> inputs = {1, 2, 3, 4, 5, 6};
+  std::vector<float> expected_result_axis0 = {
+      0.04742587, 0.04742587, 0.04742587, 0.95257413, 0.95257413, 0.95257413};
+  std::vector<float> expected_result_axis1 = {
+      0.09003057, 0.24472846, 0.66524088, 0.09003057, 0.24472846, 0.66524088};
+  input.SetExternalData({2, 3}, FDDataType::FP32, inputs.data());
+
+  // axis = 0
+  Softmax(input, &output, 0);
+  check_shape(output.shape, {2, 3});
+  check_data(reinterpret_cast<const float*>(output.Data()),
+             expected_result_axis0.data(), expected_result_axis0.size());
+
+  // axis = 1
+  Softmax(input, &output, 1);
+  check_shape(output.shape, {2, 3});
+  check_data(reinterpret_cast<const float*>(output.Data()),
+             expected_result_axis1.data(), expected_result_axis1.size());
+}
+#endif
+}  // namespace fastdeploy