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From: knutby@torle.com (P Torle)
Newsgroups: comp.lang.ada
Subject: Float precision - gnat vs objectada
Date: 1 Dec 2004 07:46:38 -0800
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Date: 2004-12-01T07:46:38-08:00
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I'm working on a Ada95/C project that shall run on both Linux and
Windows.
I have some problems getting the same float precision on both
platforms.
Example:
-----------------------------
subtype Real is Long_Float;
pi : Real;

pi := 3.14159_26535_89793_23846_26433_83279_50288_41971_69399_37511;
Real_Io.Put(pi, Aft => 25);
-----------------------------

Results:
Linux: 3.1415926535897931200000000E+00
Win32: 3.1415926535897931159979634E+00

The thing is, the following float-precision definitions are equal on
both Linux and Windows:

Real'Machine_Mantissa  : 53
Real'Machine_Emin      : -1021
Real'Machine_Emax      : 1024
Real'Digits            : 15

So why the difference? 

The Windows code is built with ObjectAda/adacomp and Microsoft tools
cl.exe/link.exe.
The Linux code is built with gnat/gcc 3.4.2