From: ara.t.howard@...
Date: 2006-08-08T01:21:40+09:00
Subject: Re: nextPowerOf2(n)

On Tue, 8 Aug 2006, Alex Young wrote:

> Robert Klemme wrote:
> <snip>
>> Did we have this solution already?
>> 
>> class Integer
>>   def next_power
>>     x = self
>>     c = 0
>> 
>>     until x == 0
>>       x >>= 1
>>       c += 1
>>     end
>> 
>>     1 << c
>>   end
>> end
> Neat, but hits an infinite loop for negative x.  Then again, that wasn't part 
> of the original problem...

easy to fix:

   harp:~ > cat a.rb
   class Integer
     def next_power_2
       return @next_power_2 if defined? @next_power_2

       x = self.abs
       c = 0

       until x == 0
         x >>= 1
         c += 1
       end

       np2 = 1 << c
       @next_power_2 = self < 0 ? -np2 : np2
     end
   end

   p 42.next_power_2
   p -42.next_power_2


   harp:~ > ruby a.rb
   64
   -64

note that it's 'vectorized' : positives move up and negatives down.

-a
-- 
to foster inner awareness, introspection, and reasoning is more efficient than
meditation and prayer.
- h.h. the 14th dali lama