add hard_tanh_layer for keras custom activation

Author: minglu2019

include/caffe/layers/hard_tanh_layer.hpp

@@ -0,0 +1,39 @@
+#ifndef CAFFE_HARD_TANH_LAYER_HPP_
+#define CAFFE_HARD_TANH_LAYER_HPP_
+
+#include <vector>
+
+#include "caffe/blob.hpp"
+#include "caffe/layer.hpp"
+#include "caffe/proto/caffe.pb.h"
+
+#include "caffe/layers/neuron_layer.hpp"
+
+namespace caffe {
+
+// implement of hard_tanh activation
+
+template <typename Dtype> class HardTanhLayer : public NeuronLayer<Dtype> {
+public:
+  explicit HardTanhLayer(const LayerParameter &param)
+      : NeuronLayer<Dtype>(param) {}
+
+  virtual inline const char *type() const { return "HardTanh"; }
+
+protected:
+  virtual void Forward_cpu(const vector<Blob<Dtype> *> &bottom,
+                           const vector<Blob<Dtype> *> &top);
+  virtual void Backward_cpu(const vector<Blob<Dtype> *> &top,
+                            const vector<bool> &propagate_down,
+                            const vector<Blob<Dtype> *> &bottom) {
+    for (int i = 0; i < propagate_down.size(); ++i) {
+      if (propagate_down[i]) {
+        NOT_IMPLEMENTED;
+      }
+    }
+  }
+};
+
+} // namespace caffe
+
+#endif // CAFFE_HARD_TANH_LAYER_HPP_

src/caffe/layers/hard_tanh_layer.cpp

@@ -0,0 +1,22 @@
+#include <math.h>
+#include <vector>
+
+#include "caffe/layers/hard_tanh_layer.hpp"
+
+namespace caffe {
+
+template <typename Dtype>
+void HardTanhLayer<Dtype>::Forward_cpu(const vector<Blob<Dtype> *> &bottom,
+                                       const vector<Blob<Dtype> *> &top) {
+  const Dtype *bottom_data = bottom[0]->cpu_data();
+  Dtype *top_data = top[0]->mutable_cpu_data();
+  for (int i = 0; i < bottom[0]->count(); ++i) {
+    top_data[i] = (bottom_data[i] > -1) ? bottom_data[i] : Dtype(-1);
+    top_data[i] = (bottom_data[i] > 1) ? Dtype(1) : top_data[i];
+  }
+}
+
+INSTANTIATE_CLASS(HardTanhLayer);
+REGISTER_LAYER_CLASS(HardTanh);
+
+} // namespace caffe