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Date: Thu, 13 Jan 2005 12:29:32 -0500
From: John Prevost <j.prevost@gmail.com>
Reply-To: John Prevost <j.prevost@gmail.com>
To: "Will M. Farr" <farr@mit.edu>
Subject: Re: [Caml-list] Ocaml sums the harmonic series -- four ways, four benchmarks: floating point performance
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On Thu, 13 Jan 2005 10:53:16 -0500, Will M. Farr <farr@mit.edu> wrote:
> Each invocation was compiled with "ocamlopt -unsafe -noassert
> -o harmonic harmonic.ml".  It looks like using references and
> loops is *by far* the fastest (and also that my PowerBook is
> pretty slow to convert int->float, but I don't think this is
> related to ocaml, since the C version does the same thing).

Note that this is dependent on what CPU you're using.  On my test
system (700MHz AMD Athlon with 256MB of memory), I saw this behavior:

time ./harmonic 1000000000:

harmonic:
  you: 2m01.590s .. 0m00.790s
   me: 0m30.811s .. 0m00.120s

harmonic2:
  you: 2m00.340s .. 0m00.440s
   me: 0m30.847s .. 0m00.140s

harmonic3:
  you: 1m44.350s .. 0m00.740s
   me: 0m38.002s .. 0m00.130s

harmonic4:
  you: 1m12.680s .. 0m00.430s
   me: 1m14.603s .. 0m00.220s

So on this system, harmonic4 is by far the slowest, and the fastest
version is the one that uses float_of_int and tail recursion.  It's
unclear to me how much of this is that the Intel compiler is simply
better optimized than the PPC compiler.

John.