From: Ryan Davis <ryand-ruby@...>
Date: 2009-02-21T07:21:34+09:00
Subject: Re: while vs loop


On Feb 20, 2009, at 13:57 , Louis-Philippe wrote:

> Hi,I saw this thread from last week: while vs loop,
>
> I don't think anybody mentioned the slight performance difference  
> between
> the two,

If you're going to talk performance differences between while and  
loop, don't forget for and each:

> % ./x.rb 1000000
> # of iterations = 1000000
>                           user     system      total        real
> each                  0.150000   0.000000   0.150000 (  0.148313)
> for                   0.170000   0.000000   0.170000 (  0.173150)
> each-var              0.230000   0.000000   0.230000 (  0.237410)
> while                 0.640000   0.010000   0.650000 (  0.644029)
> loop                  0.780000   0.000000   0.780000 (  0.785485)
> % ./x.rb 10000000
> # of iterations = 10000000
>                           user     system      total        real
> each                  1.370000   0.010000   1.380000 (  1.380012)
> for                   1.630000   0.000000   1.630000 (  1.652562)
> each-var              2.450000   0.010000   2.460000 (  2.479478)
> while                 5.510000   0.010000   5.520000 (  5.532909)
> loop                  7.730000   0.020000   7.750000 (  7.786959)


require 'benchmark'

max = (ARGV.shift || 1_000_000).to_i

puts "# of iterations = #{max}"
Benchmark::bm(20) do |x|
   x.report("each") do
     (0..max).each do
     end
   end

   x.report("for") do
     for i in 0..max do
       # do nothing
     end
   end

   x.report("each-var") do
     (0..max).each do |i|
     end
   end

   x.report("while") do
     n = 0
     while true do
       break if n >= max
       n += 1
     end
   end

   x.report("loop") do
     n = 0
     loop do
       break if n >= max
       n += 1
     end
   end
end