Re: No call for Ada (was Re: Announcing new scripting/prototyping language)

["Robert I. Eachus" <rieachus@comcast.net>]

MSG wrote:

> Can you write (*) a matrix multiplication routine in Ada, compile it
> with GNAT and measure the number CPU cycles per FLOP, compare to a
> similar routine in C?
> The shootout seems to put GNAT closer to Perl and Java than to C/C++.

As a matter of fact I am writing a fairly complex linear algebra package 
in Ada that is designed for high-performance in supercomputer type 
applications.  I probably could write it in C and stay out of the 
asylum, but it would be a close call. Why? It does things like A := A*B; 
in place, with only a row sized temporary, and using Strassen's 
algorithm with almost no copying.  For efficiency the code works not 
with an array type, but with a view that may share data with another 
view.  That way I can, for example, divide an existing matrix into four 
smaller matrices in O(1) time and space. Eventually I will also have 
code present to support both transposed views of matrices, in fact I 
just finished the fast transpose code.  That way I can transpose the 
right argument, and avoid doing it more than once.

But if I did write the same code in C, I would not expect performance to 
be better.  (There are a few cases where the parameter passing overhead 
in C would be higher, so performance would be technically worse, but 
only by a few instructions.)

> (*) Only if you think the one on the shootout page is inadequate.

Which shootout page, this one? http://dada.perl.it/shootout/matrix.html

If so the only questions I would have is why are there no default 
initial values for the matrices to insure consistancy.  (It would be 
possible for any implementation to fail unless overflow checking is 
turned off, and in Ada that can cause code to run slower.)  Incidently 
on this page, on this test gcc takes ten milliseconds, GNAT takes 20 ms. 
  Hardly in the same class as perl, 34.31 seconds, or even java, 73 
milliseconds.

Also I just submitted a new version of the strcat routine to fix a 
minor problem that resulted in the test being reported as failed.  (The 
length was printed with leading spaces, and the test harness didn't 
expect that.)  While I was at it I rewrote basically the whole thing:

with Ada.Command_Line; use Ada.Command_Line;
with Ada.Strings.Unbounded; use Ada.Strings.Unbounded;
with Ada.Strings.Fixed; use Ada.Strings;
with Ada.Text_Io; use Ada.Text_Io;
procedure Strcat is
    N: Integer;
    Hello : String := "hello" & Ascii.Lf;
begin
    if Argument_Count < 1
    then N := 10_000;
    else N := Integer'Value(Argument(1));
    end if;
    declare
      Buffer : Unbounded_String := N*Hello;
    begin
    Put_Line(Ada.Strings.Fixed.Trim
              (Integer'Image(Length(Buffer)),Left));
    end;
end Strcat;

This results in about a 100x speed up.  Is this the right way to write 
it and the code they had wrong?  In one sense, that probably is true. 
But if I use Bounded_String, the version on the website is slightly 
faster, and both versions fall midway between the fast and slow 
Unbounded versions.  (A version that just uses String is actually faster 
than the Unbounded String version.  However, I think that version is a 
bit of a cheat. ;-)

-- 
                                           Robert I. Eachus

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