From: Rick DeNatale <rick.denatale@...>
Date: 2006-10-26T10:55:56+09:00
Subject: Re: simple math question

On 10/25/06, Jeffrey Schwab <jeff@schwabcenter.com> wrote:
> Paul Lutus wrote:
> > Brad Tilley wrote:
> >
> >> Thanks for all the examples guys! Being Ruby, I thought there might be
> >> some super simple method that just magically did this. I'll stick with
> >> the old-fashioned modulo test.
> >
> > If speed matters, the modulo test is way slower than testing the LSB.
>
> Do you mean on a specific architecture, or is there a Ruby-specific
> reason for one to be slower than the other?

Not really ruby-specific, and for the most part architecture independent.

Modulo basically involves an integer division operation, whereas bit
testing is a simple logical and with a mask.

(int & 1).zero?  is probably faster than
int[0].zero?

Since the latter generates the mask using the bit position.

and both should be faster than

(int % 2).zero?

But it it's performance critical, benchmarking is recommended to
verify. One should never simply take 'rules of thumb' for granted.

-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/