From: Phrogz <gavin@...>
Date: 2006-10-26T13:15:09+09:00
Subject: Re: simple math question

Rick DeNatale wrote:
> (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.

Let's just do it rather than speculating:

require 'benchmark'

ITERATIONS = 1_000_000
MAX_INT    = 2 ** 30
NUMS = (1..ITERATIONS).map{ rand(MAX_INT) }
Benchmark.bmbm{ |x|
  x.report '(n % 2).zero?' do
    NUMS.each{ |n|
      (n % 2).zero?
    }
  end

  x.report 'n[0].zero?' do
    NUMS.each{ |n|
      n[0].zero?
    }
  end

  x.report '(n & 1).zero?' do
    NUMS.each{ |n|
      (n & 1).zero?
    }
  end
}

#=> Rehearsal -------------------------------------------------
#=> (n % 2).zero?   2.060000   0.020000   2.080000 (  2.244595)
#=> n[0].zero?      1.960000   0.010000   1.970000 (  2.145238)
#=> (n & 1).zero?   1.990000   0.020000   2.010000 (  2.275232)
#=> ---------------------------------------- total: 6.060000sec
#=>
#=>                     user     system      total        real
#=> (n % 2).zero?   2.070000   0.010000   2.080000 (  2.315105)
#=> n[0].zero?      1.960000   0.020000   1.980000 (  2.143038)
#=> (n & 1).zero?   1.990000   0.010000   2.000000 (  2.173120)

There is a very, very, very small difference in speed.