From: Kirk Haines <wyhaines@...>
Date: 2010-01-27T14:36:03+09:00
Subject: Re: Distressing Doc

On Tue, Jan 26, 2010 at 6:20 PM, lalawawa <usenet@ccjj.info> wrote:
> I was reading www.ruby-lang.org, and under "To Ruby From C and C++" it said
>
> * As of Ruby 1.8, code is interpreted at run-time rather than compiled to
> any sort of machine- or byte-code.
>
> which sounds like a huge disadvantage compared to other languages.  I did
> some testing and I get the impression that Ruby is compiling your code to
> some form of compiled version in ram before it runs it.

In the main Ruby 1.8 C implementation, it is not compiled.  It parses
the code into an abstract syntax tree, and then the interpreter
executes the code based on that AST.  In the main C 1.9.x
implementation, one's code is compiled to a byte code format.

> I made the following test programs
>
> ten_million.rb:
> #!/usr/bin/ruby -w
>
> i = 10_000_000
> while i > 0
>    i -= 1
> end

Idiom is important.

A do nothing while loop:

Benchmark.bm {|bm| bm.report {i = 10000000; while i > 0; i -= 1; end}}
      user     system      total        real
  1.840000   0.000000   1.840000 (  1.841140)


A faster way, in Ruby:

Benchmark.bm {|bm| bm.report {10000000.downto(1) {}}}
      user     system      total        real
  0.490000   0.000000   0.490000 (  0.492997)


And it's still faster, even when we make sure the value of i is
available in the block, so it's really quite equivalent to the while
loop:

Benchmark.bm {|bm| bm.report {10000000.downto(1) {|i|}}}
      user     system      total        real
  0.710000   0.000000   0.710000 (  0.707342)


In general, the MRI Ruby (the C implementation available from
ruby-lang.org) interpreter for version 1.8.x will benchmark slower
than Perl or Python on microbenchmarks, but as you can see above,
choosing the right idiom for implementation can make a large
difference.


Kirk Haines