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From: reinert@ola.npolar.no (Reinert Korsnes)
Subject: fast computing with GNAT (?)
Date: 2000/04/07
Message-ID: <8ck2ur$sgu$1@news.uit.no>#1/1
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X-Trace: news.uit.no 955092763 29214 158.39.64.31 (7 Apr 2000 07:32:43 GMT)
Organization: University of Troms�
Reply-To: Reinert.Korsnes@npolar.no
NNTP-Posting-Date: 7 Apr 2000 07:32:43 GMT
Newsgroups: comp.lang.ada
Date: 2000-04-07T07:32:43+00:00
List-Id: <comp.lang.ada>

Hi,

I am comparing GNAT and g77 on linux (RedHat 6.1).

Is it possible to use GNAT in "fast-math mode" similar 
to using g77 like this:

g77 -c -O -ffast-math -malign-double test1.f 

?


I am comparing this f77 program:
------------------------------------------
      program test1
c
      integer i
      double precision x
c     real x
      x = 10.
      n = 50000

      do 10 i = 1,10000000,1
          x = x + real(i)/1000000
          x = x*0.5 + 1 + sin(x)*cos(x) + sin(x) + cos(x) +
     -                    sin(x)*sin(x) + cos(x)*cos(x)
          if(i/n*n.eq.i) print *,i,x
 10   continue

      end
----------------------------------------------
with the following Ada program:


....................................................
with Ada.Numerics.Generic_Elementary_Functions;
with Ada.Numerics; use Ada.Numerics;
With Gnat.IO; use Gnat.IO;
with Text_IO;
procedure test1 is
   package Flt_Io is new Text_IO.Float_Io (Float);
   package E_F is new
                  Ada.Numerics.Generic_Elementary_Functions (Float);
   use E_F;
   use Flt_Io;
   n : Integer;
   x : Standard.Float;
   begin
     x := 10.0;
     n := 50000;
       for I in 1 .. 10000000 loop
          x := x + Float(I)/1000000.0;
          x := x*0.5 + 1.0 + sin(x)*cos(x) + sin(x) + cos(x) +
                             sin(x)*sin(x) + cos(x)*cos(x);
          if I mod n = 0 then
             put(I); Put (x);
             New_Line (1);
          end if;
   end loop;
end;
.......................................................

The f77 version takes about 7.5 s and the Ada version takes
about 38 s on my Linux/laptop.

The actual build commands are:

f77 -c -O4 -ffast-math -malign-double test1.f

and

gnatmake -O4 test1.adb


reinert

-- 
Norwegian Polar Institute
Polar Environment Center
N-9296 Tromso
Norway
Fax: +47 77750501

http://geophys.npolar.no/~reinert/personal.html