enable padding with custom value, default to 0

mshadow/extension/pad.h

@@ -25,13 +25,15 @@ struct PaddingExp:
   index_t pad_y_;
   /*! \brief pad size in x */
   index_t pad_x_;
+  /*! \brief value to pad with */
+  index_t value_;
   /*! \brief source tensor height */
   index_t src_height_;
   /*! \brief source tensor width */
   index_t src_width_;
   /*! \brief constructor */
-  PaddingExp(const SrcExp &src, index_t pad_y, index_t pad_x)
-      : src_(src), pad_y_(pad_y), pad_x_(pad_x) {
+  PaddingExp(const SrcExp &src, index_t pad_y, index_t pad_x, DType value)
+      : src_(src), pad_y_(pad_y), pad_x_(pad_x), value_(value) {
     this->shape_ = ShapeCheck<srcdim, SrcExp>::Check(src_);
     src_height_ = this->shape_[srcdim - 2];
     src_width_  = this->shape_[srcdim - 1];
@@ -40,38 +42,40 @@ struct PaddingExp:
   }
 };
 /*!
- * \brief padding expression, pad a image with zeros on boundaries, padding affects shape[0], and shape[1]
+ * \brief padding expression, pad an image on boundaries, padding affects shape[0], and shape[1]
  * \param src original image batches
  * \param pad padding size
+ * \param value value to pad with
  * \return expression corresponding to padded result
  * \tparam SrcExp source expression
  * \tparam DType the content data type
  * \tparam etype type of expression
  */
 template<typename SrcExp, typename DType, int etype>
 inline PaddingExp<SrcExp, DType, ExpInfo<SrcExp>::kDim>
-pad(const Exp<SrcExp, DType, etype> &src, index_t pad) {
+pad(const Exp<SrcExp, DType, etype> &src, index_t pad, DType value = static_cast<DType>(0)) {
   TypeCheckPass<ExpInfo<SrcExp>::kDim >= 2>
       ::Error_Expression_Does_Not_Meet_Dimension_Req();
-  return PaddingExp<SrcExp, DType, ExpInfo<SrcExp>::kDim>(src.self(), pad, pad);
+  return PaddingExp<SrcExp, DType, ExpInfo<SrcExp>::kDim>(src.self(), pad, pad, value);
 }
 /*!
- * \brief padding expression, pad a image with zeros on boundaries, padding affects shape[0], and shape[1]
+ * \brief padding expression, pad an image on boundaries, padding affects shape[0], and shape[1]
  * \param src original image batches
  * \param pad_y padding size in y
  * \param pad_x padding size in x
+ * \param pad value to pad with
  * \return expression corresponding to padded result
  * \tparam SrcExp source expression
  * \tparam DType the content data type
  * \tparam etype type of expression
  */
 template<typename SrcExp, typename DType, int etype>
 inline PaddingExp<SrcExp, DType, ExpInfo<SrcExp>::kDim>
-pad(const Exp<SrcExp, DType, etype> &src, index_t pad_y, index_t pad_x) {
+pad(const Exp<SrcExp, DType, etype> &src, index_t pad_y, index_t pad_x, DType value = static_cast<DType>(0)) {
   TypeCheckPass<ExpInfo<SrcExp>::kDim >= 2>
       ::Error_Expression_Does_Not_Meet_Dimension_Req();
   return PaddingExp<SrcExp, DType, ExpInfo<SrcExp>::kDim>
-      (src.self(), pad_y, pad_x);
+      (src.self(), pad_y, pad_x, value);
 }
 //----------------------
 // Execution plan
@@ -82,26 +86,28 @@ struct Plan<PaddingExp<SrcExp, DType, srcdim>, DType> {
   explicit Plan(const PaddingExp<SrcExp, DType, srcdim> &e)
       : src_(MakePlan(e.src_)),
         pad_y_(e.pad_y_), pad_x_(e.pad_x_),
+        value_(e.value_),
         new_height_(e.shape_[srcdim - 2]),
         src_height_(e.src_height_), src_width_(e.src_width_) {}
   MSHADOW_XINLINE DType Eval(index_t i, index_t j) const {
     const index_t x = j;
     const index_t y = i % new_height_;
     const index_t c = i / new_height_;
-    if (y < pad_y_ || x < pad_x_) return static_cast<DType>(0);
+    if (y < pad_y_ || x < pad_x_) return value_;
     const index_t h = y - pad_y_;
     const index_t w = x - pad_x_;
     if (h < src_height_ && w < src_width_) {
       return src_.Eval(c * src_height_ + h, w);
     } else {
-      return static_cast<DType>(0);
+      return value_;
     }
   }
 
  private:
   Plan<SrcExp, DType> src_;
   const index_t pad_y_;
   const index_t pad_x_;
+  const DType value_;
   const index_t new_height_;
   const index_t src_height_;
   const index_t src_width_;