If you look at the code I put on github, you will see I tested this exact bit of code. It does produce good assembly but I left it out because the post was alre

If you look at the code I put on github, you will see I tested this exact bit of code. It does produce good assembly but I left it out because the post was already long, and it obfuscates -why- this improvement improves performance. Your second comment (about out == in), is a bit trickier. This is obviously a contrived example. In a normal gaussian filter, you'd want the filter centered so that the effective indexes of the filter are -2 .. 2, not 0 .. 5. This makes (out == in) a trickier problem to solve. I didn't really want to get into those details in the post.