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From: Pascal Obry <p.obry@wanadoo.fr>
Newsgroups: comp.lang.ada
Subject: Re: What is faster Ada or C?
Date: 07 Dec 2001 19:12:02 +0100
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Jacob Sparre Andersen <sparre@nbi.dk> writes:

> Yes.
> 
> Related to that, I have two simple, apparantly equivalent
> programs written in respectively Ada and C++, where the GNU
> Ada and C++ compilers find it difficult to produce even
> roughly equivalent binary code or processing speed.
> 
>  * Why are the two programs below not equivalent?
>  * How can I get the Ada program to run as fast as the C++
> program?
> 
> Ada:
> 
> Compilation...: gnatmake sqrt_timer -O3 -gnatn
> Execution time: 3460 ms
> Source code:
> 
> 
> Compilation...: g++ sqrt_timer.cpp -O3
> Execution time: 1460 ms
> Source code:

You certainly want to add -gnatp to have at least two programs close enough to
compare. Note that I have the following results:

- GCC 2.95.2

   > time tsqr
   1.61803

   real  0m 0.86s
   user  0m 0.80s
   sys   0m 0.01s

- GNAT 3.x

   > time sqrt_timer
   X =  1.61803398874989E+00

   real  0m 1.38s
   user  0m 1.38s
   sys   0m 0.01s

- GNAT 5.0


   > time sqrt_timer
   X =  1.61803398874989E+00

   real  0m 1.11s
   user  0m 1.10s
   sys   0m 0.01s

I'm not an expert here but I think most of the difference between the C++ and
Ada version is in the way Sqrt is implemented. Ada put some constraints on the
Sqrt accuracy.

Anyway here the difference is not as big as what you have reported.

Pascal.

-- 

--|------------------------------------------------------
--| Pascal Obry                           Team-Ada Member
--| 45, rue Gabriel Peri - 78114 Magny Les Hameaux FRANCE
--|------------------------------------------------------
--|         http://perso.wanadoo.fr/pascal.obry
--|
--| "The best way to travel is by means of imagination"