From: Intransition <transfire@...>
Date: 2010-02-07T00:03:20+09:00
Subject: Re: Fastest way to iterate over a range in steps



On Feb 6, 8:40 am, Robert Klemme <shortcut...@googlemail.com> wrote:
> On 02/05/2010 09:19 PM, Intransition wrote:
>
>
>
> > On Feb 5, 2:52 pm, Robert Klemme <shortcut...@googlemail.com> wrote:
>
> >> I think we are seeing an effect of the missing call to the block that
> >> happens on each iteration for #step approaches.  The while loop does not
> >> have this overhead.
>
> > Might consider how #succ plays into this as well.
>
> Good idea!
>
> robert@fussel:~$ ruby19 xx.rb
> Rehearsal --------------------------------------------------
> while           15.550000   0.060000  15.610000 ( 22.225998)
> succ            66.930000   0.340000  67.270000 ( 93.726408)
> range step      31.930000   0.080000  32.010000 ( 44.892588)
> step            30.650000   0.140000  30.790000 ( 43.183693)
> --------------------------------------- total: 145.680000sec
>
>                       user     system      total        real
> while           15.430000   0.080000  15.510000 ( 21.889805)
> succ            67.170000   0.440000  67.610000 ( 95.958702)
> range step      32.090000   0.160000  32.250000 ( 44.213130)
> step            30.670000   0.110000  30.780000 ( 43.151260)
> robert@fussel:~$ cat xx.rb
>
> require 'benchmark'
>
> LI = 1000000000
> ST = 5
>
> Benchmark.bmbm 15 do |b|
>    b.report "while" do
>      i = 0
>      while i < LI
>        i += ST
>      end
>    end
>
>    b.report "succ" do
>      i = 0
>      while i < LI
>        i = i.succ
>      end
>    end
>
>    b.report "range step" do |b|
>      (0...LI).step ST do |i|
          i
>      end
>    end
>
>    b.report "step" do |b|
>      0.step LI, ST do |i|
          i
>      end
>    end
> end

To be fair maybe add a reference to i.

> robert@fussel:~$
>
> ... or rather not. :-)

Good to know too. Though actually I was wondering if range#step uses
#succ? I think in the case of integers it's optimized to not use
#succ, but there can be different types of ranges (eg. String ranges)
and in those cases it does. Sometime back I suggested that #succ take
an optional parameter to specify how many times to #succ. This would
allow classes like Fixnum to optimize multiple steps.

In any case I find it striking how much faster while is. It's
understandable that there is some overhead accompany the use of a
block. But that much?