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From: Jacob Sparre Andersen <sparre@nbi.dk>
Newsgroups: comp.lang.ada
Subject: Re: What is faster Ada or C?
Date: Fri, 07 Dec 2001 14:21:47 +0100
Organization: Centre for Chaos and Turbulence Studies, Niels Bohr Institute
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Date: 2001-12-07T14:21:47+01:00
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Jeffrey Carter wrote:

> Robert Dewar has stated here on several occasions that he has some
> equivalent Ada and C programs that produce identical object code when
> compiled with gcc.

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:

with Ada.Numerics.Generic_Elementary_Functions;
with Ada.Text_IO;
with Interfaces.C;

procedure Sqrt_Timer is

   type Scalar is new Interfaces.C.Double;

   package Math is new
Ada.Numerics.Generic_Elementary_Functions (Scalar);

   function Sqrt (Item : in Scalar) return Scalar renames
Math.Sqrt;
   pragma Inline (Sqrt);

   X : Scalar := 2.0;

begin  --  Sqrt_Timer
   for i in 1 .. 10_000_000 loop
      X := Sqrt (1.0 + X);
   end loop;

   Ada.Text_IO.Put_Line ("X = " & Scalar'Image (X));
end Sqrt_Timer;


C++
===

Compilation...: g++ sqrt_timer.cpp -O3
Execution time: 1460 ms
Source code:

#include <math.h>
#include <iostream.h>

int main (int argl,char* argv[]) {

   double x=2.0;

   for(int i=0;i<10000000;i++){
      x=sqrt(1.0+x);
   };

   cout << x << endl;
};


Jacob
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