Strange code in Fast Keypoint detector: (i - 3) % 3

C++
1

I see this code here:

Am I missing something or is it an artifact that remained there after debugging?

2

curr is being used two lines down, so no, that’s not dead code.

it is some funky math but seems intentional.

remember, the % operator in C and C++ has weird semantics. (-1) % 3 == -1

3

We have i >=3 always

I am not saying it’s dead. I am saying that we could simply write i % 3 instead.

4

oh right, I’m not quite awake yet. so… it’s index shifting. and the shift shows up in that place, as it should, but it’s all magic constants, which is bad.

such code deserves a few more comments.

anyway, any reasonable compiler will optimize that, so nothing to worry about.