[GitHub] piiswrong commented on a change in pull request #8759: image flip op

[GitBox <gi...@apache.org>]

piiswrong commented on a change in pull request #8759: image flip op
URL: https://github.com/apache/incubator-mxnet/pull/8759#discussion_r152694849
 
 

 ##########
 File path: src/operator/image/image_random-inl.h
 ##########
 @@ -144,6 +151,45 @@ static void Normalize(const nnvm::NodeAttrs &attrs,
   });
 }
 
+inline static int FlipIndex(int idx, const int stride, const int trailing) {
+  const int low = idx % trailing;
+  int high = idx / trailing;
+  const int x = high % stride;
+  high /= stride;
+
+  return (high * stride + stride - 1 - x) * trailing + low;
+}
+
+template<typename DType>
+static void FlipImpl(const int size, DType *src, DType *dst,
+                     const int stride, const int trailing) {
+  for (int idx = 0; idx < size; ++idx) {
+    int new_idx = FlipIndex(idx, stride, trailing);
 
 Review comment:
   Doing this on every index is slow. Either use two loops explicitly or use `inc`, see broadcasting for example

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