[cwn] Attn: Development Editor, Latest Caml Weekly News
Alan Schmitt
alan.schmitt at polytechnique.org
Tue Feb 15 01:15:16 PST 2005
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Hello,
Here is the latest Caml Weekly News, for the week of 08 to 15 February,
2005.
1) [Benchmark] NBody
2) OCaml-HTTP 0.1.0
3) String to list to string
4) Contract position in compiler development available, MSR Cambridge
========================================================================
1) [Benchmark] NBody
Archive: http://caml.inria.fr/archives/200502/msg00233.html
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** Christophe Troestler said and Xavier Leroy answered:
> For fun I have implemented an nbody simulation following
>
http://shootout.alioth.debian.org/benchmark.php?
test=nbody&lang=all&sort=cpu
> (code is attached).
Ah, another micro-benchmark. Great pasttime!
Your OCaml code is about as good as you can write. All the unboxing
optimizations are triggered.
> ocamlopt -o nbody.com -inline 3 -unsafe -ccopt -O2 nbody.ml
On x86, you can get a bit more speed with -ffast-math, which turns the
call to sqrt() into inline assembly. As others mentioned, "-ccopt -O2"
is useless.
> I've compared with the Java program they give. I get (on a Pentium(R)
> 4 CPU 2.40GHz Debian):
>
> n OCaml Java
> 1000 0.004 0.112
> 10000 0.016 0.112
> 100000 0.159 0.218
> 200000 0.284 0.370
> 500000 0.707 0.702
> 1000000 1.410 1.359
> 2000000 2.884 2.453
> 3000000 4.294 3.590
> 4000000 5.735 4.774
>
> I am interested in explanations why OCaml seems asymptotically slower
> than Java and ways to improve that.
You don't say which Java implementation you used (there are several).
The "0.112" overhead of Java corresponds to start-up time, which
includes
JIT-compilation. As to why Java is asymptotically faster, we'd
need to look at the generated assembly code. Good luck doing that
with a JIT compiler.
So, to understand OCaml's performances here, one has to turn to a
different baseline. I translated your Caml code to C and looked at
gcc output.
The best gcc output is faster than the best OCaml output by about 30%.
Looking at the asm code, the main difference is that gcc keeps some
float variables (dx, dy, dz, etc) in the floating-point stack while
OCaml stores them (unboxed) to the stack. Maybe the Java
implementation you used manages to use the float stack. Who knows.
The x86 floating-point stack is an awfully bad match for the
register-based OCaml code generation model, so, no, I'm not going to
the great lengths the gcc folks went to extract some performance from
that model.
(Besides, being 1.3 times slower than gcc on numerical code is within
the design envelope for OCaml. My performance goals have always been
"never more than twice as slow as C".)
On a "normal" (register-based) float architecture like PowerPC or
x86_64, the OCaml-generated code is essentially identical to the
gcc-generated one.
The C translation is attached for your amusement.
(please see the archives for the code - the editor)
========================================================================
2) OCaml-HTTP 0.1.0
Archive: http://caml.inria.fr/archives/200502/msg00279.html
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** Stefano Zacchiroli announced:
OCaml-HTTP is an Objective Caml library freely inspired from perl's
HTTP::Daemon module that enables creation of simple HTTP daemons in
OCaml.
I just released version 0.1.0, download and more information available
at the following links:
- - webpage http://www.bononia.it/~zack/ocaml-http.en.html
- - tarball http://www.bononia.it/~zack/stuff/ocaml-http-0.1.0.tar.gz
- - changelog http://www.bononia.it/~zack/stuff/ocaml-http/changelog
- - API doc
http://www.bononia.it/~zack/stuff/ocaml-http/html/index.html
========================================================================
3) String to list to string
Archive: http://caml.inria.fr/archives/200502/msg00302.html
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** Juancarlo Añez asked and William D.Neumann answered:
> Why aren't there functions in the standard library to convert strings
> to lists of characters and back?
Because a) they're not all that useful and b) they're trivial to write
for yourself:
let explode s =
let rec exh acc = function
| -1 -> acc
| i -> exh (s.[i]::acc) (pred i)
in exh [] (pred (String.length s))
let implode l =
let s = String.create (List.length l) in
let rec imh i = function
| h::t -> s.[i] <- h; imh (succ i) t
| [] -> s
in imh 0 l
** Erik de Castro Lopo replied:
Here's one thats a little more obvious (remove the function, use
String.get)
and runs about 20% faster (at least on my iBook running Linux):
let string_to_charlist str =
let rec stc lst n =
if n < 0 then lst
else stc ((String.get str n) :: lst) (n - 1)
in
stc [] ((String.length str) - 1)
;;
To be honest, this was my second attempt. My first attempt was slower
than yours and blew the stack on million character strings (obviously
not tail rescursive). This one (and yours) is quite happy with strings
10 times that size.
** Radu Grigore answered:
Yet another one:
http://caml.inria.fr/FAQ/FAQ_EXPERT-eng.html#strings
** Jon Harrop suggested:
If you want succinct implementations then I'd go for:
let char_list_of_string s =
let l = ref [] in
String.iter (fun c -> l := c :: !l) s;
List.rev !l
let string_of_char_list l =
String.concat "" (List.map (String.make 1) l)
** Richard Jones also replied:
As others have said, these functions are not in the standard library.
However, useful functions like these[1] are available in Extlib, which
you can find here:
http://sourceforge.net/projects/ocaml-lib/
and is also available as a binary package for various platforms such
as Debian.
It contains important functions such as String.map,
String.replace_chars, String.slice, String.starts_with,
String.ends_with, and many more.
Rich.
[1] Although embarrassingly, it appears, not these exact functions,
which is why I've CC'd to ocaml-lib-devel list. To ocaml-lib-devel:
we should provide implementations of
http://caml.inria.fr/FAQ/FAQ_EXPERT-eng.html#strings
========================================================================
4) Contract position in compiler development available, MSR Cambridge
Archive: http://caml.inria.fr/archives/200502/msg00339.html
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** Don Syme announced:
Dear OCaml-list,
This is a job opportunity for an ML programmer, and may be of particular
interest to those who love compiler development for functional
languages.
Thanks
Don
Contract position in compiler development
Microsoft Research, Cambridge, UK
MSR Cambridge has available a 6 month contract position in applied
language
design, optimization and compiler development for work on the F#
project. F#
is a variant of the ML functional programming language with core subset
essentially compatible with the core of the OCaml language, along with a
compiler and tools for the .NET platform and Visual Studio. It is
specifically
designed to facilitate cooperation between ML code and other .NET
languages
such as C# and can be downloaded from
http://research.microsoft.com/downloads .
F# is also being used by several projects within Microsoft and Microsoft
Research. More information on F# can be found at
http://research.microsoft.com/projects/fsharp .
We are looking for candidates with some or all of the following
qualifications:
* MS. or Ph.D. in Computer Science
* Strong applied ML or functional programming skills, in Standard
ML,
OCaml, F# or Haskell. Some experience with C++ is also required.
* Knowledge of algorithms and techniques from compilers, including
experience with the design and implementation of inference-based
type
systems
* Good communication and inter-personal skills
* Leadership and cross-team collaboration skills, including a
desire to
work with Microsoft product teams and external partners in
training them
in the use of the language and tools.
* 2 years of industrial experience, including the ability to
self-manage
through the progressive release of stable versions of a product
* A strong desire to ensure that mixed functional/imperative
programming is
a viable reality on the .NET platform
* Excitement at the potential that the libraries and tools of the
.NET
Framework and Visual Studio offer to niche programming languages
This position will be tailored according to the skills of the
candidate, but
will include key activities such as the following:
- - Maintaining the language and runtime infrastructure
o Fixing bugs in the F# code base
o Implementing new features in F#, including the Visual Studio tools
for F#
o Responding to customer feature requests
o Improving the performance of programs compiled with F#
- - Technology transfer from Microsoft Research
o Working with key F# customers within Microsoft Research and the
product
divisions
The candidate must be willing to work in Cambridge and travel as needed
to the
Seattle area and elsewhere.
Applications should be sent to Alex Reed (alreed at microsoft.com)
F# is a contribution by Microsoft Research to ensure that a strong
ML-like
symbolic programming language is available in the context of .NET. Our
group
has a good track record of positively influencing the design and
implementation
of Microsoft's programming languages and platforms. As such this
position
offers the candidate the chance to make a major contribution to how
future
developers write programs and to the quality of the software that we
use, both
directly through ML as a language and indirectly through the research
agenda of
the academic community from which it stems.
========================================================================
Using folding to read the cwn in vim 6+
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Here is a quick trick to help you read this CWN if you are viewing it
using
vim (version 6 or greater).
:set foldmethod=expr
:set foldexpr=getline(v:lnum)=~'^=\\{78}$'?'<1':1
zM
If you know of a better way, please let me know.
========================================================================
Old cwn
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========================================================================
Alan Schmitt, http://sardes.inrialpes.fr/~aschmitt/
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