Arrays magic number 16 and queue or when ruby can be faster than ruby

gistfile1.txt

# This notebook is on Atom N270 1.33GHz, so that I use only 500000 iterations
~/tmp/ruby$ ruby test_queue.rb 500000
Rehearsal -------------------------------------------------------------
pure man queue 2            0.570000   0.000000   0.570000 (  0.574775)
pure man queue 4            0.550000   0.000000   0.550000 (  0.557201)
pure man queue 15           0.600000   0.000000   0.600000 (  0.599789)
pure man queue 16           1.620000   0.000000   1.620000 (  1.615062)
pure man queue 48           1.720000   0.000000   1.720000 (  1.729971)
pure man queue 128          2.130000   0.000000   2.130000 (  2.136135)
pure ruby smart queue 4     1.170000   0.000000   1.170000 (  1.166562)
pure ruby smart queue 15    1.190000   0.000000   1.190000 (  1.196802)
pure ruby smart queue 16    1.330000   0.000000   1.330000 (  1.336846)
pure ruby smart queue 48    1.440000   0.000000   1.440000 (  1.439500)
pure ruby smart queue 128   1.480000   0.000000   1.480000 (  1.505486)
compiled queue 4            0.730000   0.020000   0.750000 (  0.744997)
compiled queue 15           0.780000   0.030000   0.810000 (  0.900667)
compiled queue 16           0.780000   0.020000   0.800000 (  0.830441)
compiled queue 48           0.840000   0.040000   0.880000 (  0.946987)
compiled queue 128          0.800000   0.020000   0.820000 (  0.845067)
--------------------------------------------------- total: 17.860000sec

                                user     system      total        real
pure man queue 2            0.700000   0.000000   0.700000 (  0.699771)
pure man queue 4            0.710000   0.010000   0.720000 (  0.722799)
pure man queue 15           0.790000   0.000000   0.790000 (  0.793402)
pure man queue 16           1.960000   0.000000   1.960000 (  1.975780)
pure man queue 48           1.970000   0.000000   1.970000 (  1.979116)
pure man queue 128          2.240000   0.000000   2.240000 (  2.247744)
pure ruby smart queue 4     1.300000   0.000000   1.300000 (  1.297341)
pure ruby smart queue 15    1.240000   0.000000   1.240000 (  1.244382)
pure ruby smart queue 16    1.380000   0.000000   1.380000 (  1.389162)
pure ruby smart queue 48    1.370000   0.010000   1.380000 (  1.390153)
pure ruby smart queue 128   1.540000   0.000000   1.540000 (  1.551731)
compiled queue 4            0.680000   0.010000   0.690000 (  0.686393)
compiled queue 15           0.690000   0.010000   0.700000 (  0.704052)
compiled queue 16           0.700000   0.010000   0.710000 (  0.702106)
compiled queue 48           0.730000   0.020000   0.750000 (  0.748439)
compiled queue 128          0.710000   0.020000   0.730000 (  0.732491)

~/tmp/ruby$ ruby -v
ruby 1.9.3p125 (2012-02-16 revision 34643) [i686-linux]

test_queue.rb

require 'benchmark'
# https://github.com/kanwei/algorithms
require 'algorithms'

N = (ARGV[0] || 1000000).to_i

def test(a)
  N.times{|i| a.shift; a.push i}
end

# Array - is a pure man queue
def ar(n)
  [1] * n
end

# Consider Array bad magic number "16"
class Deque
  def initialize(enum)
    @cont = enum.each_slice(15).to_a
    unless @cont.empty?
      @first = @cont.shift
    else
      @first = []
    end
    unless @cont.empty?
      @last = @cont.last
    else
      @last = @first
    end
  end
  def push(v)
    last = @last
    if last.size == 15
      @cont << (@last = [v])
    else
      last << v
    end
  end
  def shift
    first = @first
    v = first.shift
    if first.empty? && !@cont.empty?
      @first = @cont.shift
    end
    v
  end
end

def deq(n)
  Deque.new(ar(n))
end

# use compilled queue
class Containers::CDeque
  alias shift pop_front
  alias push push_back
end
def adeq(n)
  Containers::CDeque.new(ar(n))
end

Benchmark.bmbm(6) do |x|
  x.report('pure man queue 2'){ test(ar(2)) }
  x.report('pure man queue 4'){ test(ar(4)) }
  x.report('pure man queue 15'){ test(ar(15)) }
  x.report('pure man queue 16'){ test(ar(16)) }
  x.report('pure man queue 48'){ test(ar(48)) }
  x.report('pure man queue 128'){ test(ar(128)) }
  x.report('pure ruby smart queue 4'){ test(deq(4)) }
  x.report('pure ruby smart queue 15'){ test(deq(15)) }
  x.report('pure ruby smart queue 16'){ test(deq(16)) }
  x.report('pure ruby smart queue 48'){ test(deq(48)) }
  x.report('pure ruby smart queue 128'){ test(deq(128)) }
  x.report('compiled queue 4'){ test(adeq(4)) }
  x.report('compiled queue 15'){ test(adeq(15)) }
  x.report('compiled queue 16'){ test(adeq(16)) }
  x.report('compiled queue 48'){ test(adeq(48)) }
  x.report('compiled queue 128'){ test(adeq(128)) }
end