[#122973] [PATCH] Add Gem.default_install — Felipe Contreras via ruby-core <ruby-core@...>
We need a way to enable user installs by default so that tools like
3 messages
2025/08/17
[ruby-core:123119] [Ruby Feature#20163] Introduce #bit_count method on Integer
From:
"tompng (tomoya ishida) via ruby-core" <ruby-core@...>
Date:
2025-08-29 12:46:08 UTC
List:
ruby-core #123119
Issue #20163 has been updated by tompng (tomoya ishida).
I also think popcount of a negative number should raise error because of the ambiguity.
One way to extend popcount to negative number is using a relationship below, derived from the fact that `-5 == 0b111...11111011` has 1 fewer bits compared to `-1 == 0b111...11111111`.
~~~ruby
x.popcount == popcount_of_minus_one - (~x).popcount
# popcount_of_minus_one: 0 or -1 or something else representing infinity bits
~~~
I'm not sure if this definition is useful, but anyway, extending to negative number has ambiguity.
If someone want a popcount of abs, `n.abs.popcount` is clearer.
----------------------------------------
Feature #20163: Introduce #bit_count method on Integer
https://bugs.ruby-lang.org/issues/20163#change-114447
* 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
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