Issue #20163 has been updated by mame (Yusuke Endoh). What are the intended use cases for this proposal? My experience (in other languages) involves two use cases of popcount: * Bitboards for game AI (like Reversi) to count pieces. * Succinct data structures (like LOUDS Tries) for rank operations. In both scenarios, integers are treated as unsigned bitsets. Does anyone have a use case where popcount on a negative number is necessary? If not, I guess raising an exception would be the best behavior. ---------------------------------------- Feature #20163: Introduce #bit_count method on Integer https://bugs.ruby-lang.org/issues/20163#change-114446 * Author: garrison (Garrison Jensen) * Status: Open ---------------------------------------- This feature request is to implement a method called #bit_count on Integer that returns the number of ones in the binary representation of the absolute value of the integer. ``` n = 19 n.bit_count #=> 3 (-n).bit_count #=> 3 ``` This is often useful when you use an integer as a bitmask and want to count how many bits are set. This would be equivalent to ``` n.to_s(2).count("1") ``` However, this can be outperformed by ``` def bit_count(n) count = 0 while n > 0 n &= n - 1 # Flip the least significant 1 bit to 0 count += 1 end count end ``` I think this would be a useful addition because it would fit alongside the other bit-related methods defined on integer: `#bit_length,` `#allbits?`, `#anybits?`, `#nobits?`. Also, when working with bitmasks, a minor upgrade to performance often results in a significant improvement. Similar methods from other languages: https://docs.python.org/3/library/stdtypes.html#int.bit_count https://doc.rust-lang.org/std/primitive.i32.html#method.count_ones -- https://bugs.ruby-lang.org/