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From: "Nasser M. Abbasi" <nma@12000.org>
Newsgroups: comp.lang.ada
Subject: getting same output as gfortran, long_float
Date: Thu, 30 Apr 2015 16:17:49 -0500
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Xref: news.eternal-september.org comp.lang.ada:25665
Date: 2015-04-30T16:17:49-05:00
List-Id: <comp.lang.ada>

I am learning Ada again, and was wondering what do I need to change
in this small code to make it output the same precision as gfortran?

First I show the code, then explain more what the issue.

Fortran:

--------------------
PROGRAM foo
IMPLICIT NONE
INTEGER, PARAMETER :: DBL = KIND(1.D0)
REAL(KIND = DBL) :: x
   x = 12.0D0 * 0.0001D0/(1.0D0 * (1.0D0 - 0.1D0)**4 )
PRINT *, x
END PROGRAM
-------------------

Now, gfortran has an option called -fdefault-real-8 which I thought
will map to Ada long_float.

https://gcc.gnu.org/onlinedocs/gfortran/Fortran-Dialect-Options.html
"-fdefault-real-8 Set the default real type to an 8 byte wide type."

When compiling and running the above Fortran program, this is the output

-------------------
gfortran -Wall -fdefault-real-8  foo2.f90
./a.out
    1.82898948331047096479195244627343369E-0003

gfortran -Wall  foo2.f90
./a.out
    1.8289894833104711E-003
----------------------------------------

It is the first result above I'd like to get with Ada. Here is
what I tried:

--------------------
with ada.text_io; use ada.text_io;
procedure foo_2 is
   x : Long_Float;
begin
   x := 12.0 * 0.0001/(1.0 * (1.0 - 0.1)**4 );
   put_line(long_float'image(x));
end foo_2;
----------------------

compile and run:

gnatmake foo_2.adb
gcc-4.8 -c foo_2.adb
gnatbind -x foo_2.ali
gnatlink foo_2.ali
./foo_2
  1.82898948331047E-03


side-by-side:
=============
Ada (long)                1.82898948331047E-03
Ada (long long)           1.82898948331047096E-03
Fortran:                  1.8289894833104711E-003
Fortran -fdefault-real-8: 1.82898948331047096479195244627343369E-0003

How to obtain the last result above in Ada?

ps. here is the long_long_float Ada version.

-------------
with ada.text_io; use ada.text_io;
procedure foo_2 is
   x : Long_Long_Float;
begin
   x := 12.0 * 0.0001/(1.0 * (1.0 - 0.1)**4 );
   put_line(Long_Long_Float'image(x));
end foo_2;
----------------

--Nasser