From: Rick DeNatale <rick.denatale@...>
Date: 2006-08-08T00:24:49+09:00
Subject: Re: nextPowerOf2(n)

On 8/7/06, Daniel Schierbeck <daniel.schierbeck@gmail.com> wrote:
> Ch Skilbeck wrote:
> > def nextPowerOf2(n)
> >   raise "integer please" if !n.kind_of? Integer
> >   high = 0
> >   count = 0
> >   (0..n.size * 8 - 2).each {|b| count += n[b] ; high = b if n[b] != 0}
> >   1 << high + (count > 1 ? 1 : 0)
> > end
>
> Your question has already been answered by Simon, but I'd like to show
> you how your code could be more Rubyesque.
>
> First off, method name are always lower_case_with_underscore, so
>
>    def next_power_of_2(n)
>
> Ruby has the `unless' keyword, so
>
>    raise "integer please" unless n.kind_of? Integer
>
> but you don't really have to check the argument's class -- just check if
> the provided object responds to #to_int, or don't even check at all.
>
>    raise "integer please" unless n.respond_to? :to_int
>    n = n.to_int
>
> Parallel assignment is cool
>
>    high, count = 0, 0
>
> I'd split the next part up, but that may just be me
>
>    (0..(n.size * 8 - 2)).each do |b|
>      count += n[b]
>      high = b unless n[b] == 0
>    end
>
> Just some thoughts

Here's another take

irb(main):016:0> class Fixnum
irb(main):017:1>     def next_power_of_2
irb(main):018:2>       trial = 1
irb(main):019:2>       trial <<= 1 while trial < self
irb(main):020:2>       return trial
irb(main):021:2>     end
irb(main):022:1> end
=> nil
irb(main):023:0> (-1..10).collect { | i | [i, i.next_power_of_2] }
=> [[-1, 1], [0, 1], [1, 1], [2, 2], [3, 4], [4, 4], [5, 8], [6, 8],
[7, 8], [8, 8], [9, 16], [10, 16]]
irb(main):024:0>

This should be fairly fast since at first glance it's o(log2(n))

And it makes it a method of Fixnum

-- 
Rick DeNatale

IPMS/USA Region 12 Coordinator
http://ipmsr12.denhaven2.com/

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