how to find similarity of two patches?

In Non Local Total Variation, a fixed patch is exploited to search the non-local similar patches for each pixel. Suppose the patch size is p*p, P(x) represents the vector form of the target patch centered at the location x, we find for the similar patch P(y) in a w*w search window around x.

[Helal Uddin Mullah]

Can any one kindly give an example with the loop for Finding similar patches?

similarity condition: either of normalized cross correlation or Euclidian distance.