Fix elementwise add bug for genet model

src/operators/kernel/central-arm-func/elementwise_add_arm_func.h

@@ -38,20 +38,31 @@ void ElementwiseAddCompute(const ElementwiseAddParam<CPU> &param) {
   Out->mutable_data<float>();
   int axis = param.Axis();
 #if defined(__ARM_NEON__) || defined(__ARM_NEON)
+  const auto &x_dims = input_x->dims();
+  const auto &y_dims = input_y->dims();
+  /// axis = -1 represent the last dimensions.
+  axis = (axis == -1 ? x_dims.size() - y_dims.size() : axis);
   size_t batch = 1;
+  size_t channels = 1;
   size_t elementwise_num = 1;
   for (int i = 0; i < axis; ++i) {
-    batch *= input_x->dims()[i];
+    batch *= x_dims[i];
   }
-  for (int i = axis + 1; i < input_x->dims().size(); ++i) {
-    elementwise_num *= input_x->dims()[i];
+  for (int i = 0; i < y_dims.size(); ++i) {
+    channels *= y_dims[i];
   }
+  for (int i = y_dims.size() + axis; i < x_dims.size(); ++i) {
+    elementwise_num *= x_dims[i];
+  }
+  const float *bias_data = input_y->data<float>();
+  const float *input_data = input_x->data<float>();
+  float *output_data = Out->mutable_data<float>();
   for (int i = 0; i < batch; ++i) {
-    for (int j = 0; j < input_x->dims()[axis]; ++j) {
-      size_t offset = (i * input_x->dims()[axis] + j) * elementwise_num;
-      const float *input = input_x->data<float>() + offset;
-      const float *bias = input_y->data<float>() + j;
-      float *output = Out->mutable_data<float>() + offset;
+    for (int j = 0; j < channels; ++j) {
+      size_t offset = (i * channels + j) * elementwise_num;
+      const float *input = input_data + offset;
+      const float *bias = bias_data + j;
+      float *output = output_data + offset;
 
       int loop = elementwise_num >> 0x4;
       int remain = elementwise_num & 0xF;