Why Numba doesn't improve this recursive function

Question

I have an array of true/false values with a very simple structure:

# the real array has hundreds of thousands of items
pos         


        

Answer 1

The gist is, only the part of logic that uses Python machinery can be accelerated -- by replacing it with some equivalent C logic that strips away most of the complexity (and flexibility) of Python runtime (I presume this is what Numba does).

All the heavy lifting in NumPy operations is already implemented in C and very simple (since NumPy arrays are contiguous chunks of memory holding regular C types) so Numba can only strip the parts that interface with Python machinery.

Your "binary search" algorithm does much more work and makes much heavier use of NumPy's vector operations while at it, so less of it can be accelerated this way.