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Date: Sat, 6 Apr 2002 14:52:38 +0200 (MET DST)
From: Kevin Santugini <Kevin.Santugini@dptmaths.ens-cachan.fr>
To: freebsd-questions@FreeBSD.ORG
Subject: double having the same precision as  long double (C questions)
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but not the same size..

Hello,

I'm not sure if it should be posted on freebsd-questions or in bugs or to
gcc-mailing lists. But I have heard that the limits.h and float.h headers
are supplied by the system and not by the compiler.

I'm running Freebsd 4.5 Release  and I use the gcc supplied with the
base system (gcc 2.95.3).

We have:
sizeof(double)=8
sizeof(long double)=12

So a long double use 4 more bytes than a double to store its data.

However <float.h> states that double and long double
have the same properties (epsilon, min, max, digits in mantisse and digits
in double). A small test program show that the header is right about the
precision and the properties of double and long double.

And pointer's arithmetic show that sizeof is right too.

So a long double uses four more bytes than a double for no extra
precision.

This seems a little odd to mee. Why use four more bytes if we
don't achieve better precision?

Kevin Santugini

PS:I have also noted that the C++ header <limits> defining
the template numeric_limits doesn't exist either. However, it is easy to
build one from the C headers..




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