From: Tanaka Akira <akr@...>
Date: 2013-08-09T09:42:21+09:00
Subject: [ruby-core:56463] Re: [ruby-trunk - Feature #8738] Integer#single_bit? (Actually Fixnum#single_bit? and Bignum#single_bit?)

2013/8/5 stomar (Marcus Stollsteimer) <redmine@ruby-lang.org>:
> Issue #8738 has been updated by stomar (Marcus Stollsteimer).

> Regarding the naming, I find
>
>   8.single_bit?  # => true
>
> a little strange (that's 4 bits), power_of_2?/power_of_two? seem to be more to the point.

I feel power_of_two? returns false for all negative numbers.
But I want to determine negative powers of two.

So, if power_of_two? method will be added, I'd like to add
negative_power_of_two? method too.
(It returns true for -1, -2, -4, ...)

negative_power_of_two? can be combined with bit_length (absolute number) as
  n.negative_power_of_two? ? n.bit_length <= 32 : n.bit_length < 32
to determine n fits in 32 bits signed integer with two's complement format.

It can be combined with bit_length (two's complement) as
  n.negative_power_of_two? ? n.bit_length < 53 : n.bit_length <= 53
to determine n fits in 53 bits integer with absolute number format.
-- 
Tanaka Akira