From: "tenderlovemaking (Aaron Patterson) via ruby-core" Date: 2025-10-24T19:04:27+00:00 Subject: [ruby-core:123539] [Ruby Feature#20163] Introduce #bit_count method on Integer Issue #20163 has been updated by tenderlovemaking (Aaron Patterson). matz (Yukihiro Matsumoto) wrote in #note-24: > Is there any real-world use-case for Integer#popcount method? > Bit-array? > > Matz. Yes, I am using it for a [bit set gem](https://github.com/tenderlove/bitz) (I had to implement my own popcount [here](https://github.com/tenderlove/bitz/blob/3570f8dfd3aec46bc9ffac03ef5e85fb26cc27a3/lib/bitz/set.rb#L331-L336)). I want to use a bit array for representing an undirected graph. ---------------------------------------- Feature #20163: Introduce #bit_count method on Integer https://bugs.ruby-lang.org/issues/20163#change-114917 * 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/ ______________________________________________ ruby-core mailing list -- ruby-core@ml.ruby-lang.org To unsubscribe send an email to ruby-core-leave@ml.ruby-lang.org ruby-core info -- https://ml.ruby-lang.org/mailman3/lists/ruby-core.ml.ruby-lang.org/