Hi All,
I am working <https://github.com/numpy/numpy/pull/19355> on a new UFunc, ` bit_count <https://en.wikipedia.org/wiki/Hamming_weight>` (popcount in other languages) that aims to count the number of 1-bits in the absolute value of an Integer. Implementation ---------------------------------- The primary reference for the implementation is CountBitsSetParallel <http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel>. Here we take 12 operations to achieve the result which is the same as the lookup table method but does not suffer from memory issues or cache misses. The implementation is aimed at unsigned integers, absolute value of signed integers and objects that support the operation. Usage -------------- >>> np.bit_count(1023) 10 >>> a = np.array([2**i - 1 for i in range(16)]) >>> np.bit_count(a) array([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]) >>> np.int32(1023).bit_count() 10 Notes ------------- 1. Python has included this method here <https://github.com/python/cpython/commit/8bd216dfede9cb2d5bedb67f20a30c99844dbfb8> (3.10+). Tracking issue <https://bugs.python.org/issue29882> 2. NumPy tracking issue <https://github.com/numpy/numpy/issues/16325> 3. Interesting read <https://archive.org/details/dr_dobbs_journal_vol_08/page/n185/mode/2up> on how we get the magic number. Needed a bit of digging :) Please let us know what you think about the implementation and where we can improve in terms of performance or interface. Regards, Ganesh
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