Finding the angle between two vectors is not hard using the cosine rule. However, because I am programming for a platform with very limited resources, I would like to avoid calculations such as sqrt and arccos. Even simple divisions should be limited as much as possible.
Fortunately, I do not need the angle per se, but only need some value that is proportional to said angle.
So I am looking for some computationally cheap algorithm to calculate a quantity that is related to the angle between two vectors. So far, I haven't found something that fits the bill, nor have I been able to come up with something myself.