Question

C++ has a set of functions, ffs(), ffsl(), and ffsll(), that return the least significant bit that is set in a given binary integer.

I’m wondering if there is an equivalent function already available in Python. I don’t see one described for bitarray, but perhaps there’s another. I am hoping to avoid calculating the answer by looping through all possible bit masks, though of course that’s an option of last resort; ffs() simply returns a single integer and I’d like to know of something comparable in Python.

Answer 1

It is available in the gmpy wrapper for the GNU Multi-Precision library. On my system, it is about 4x faster than the ctypes solution.

>>> import gmpy
>>> gmpy.scan1(136)
3
>>> bin(136)
'0b10001000'