From: Morten Welinder <terra AT diku DOT dk>
Date: Mon, 2 Jan 1995 10:06:02 +0100
To: IBBT0 AT cc DOT uab DOT es
Cc: djgpp AT sun DOT soe DOT clarkson DOT edu
Subject: Re: Why this bug?


(Please check your mail software -- it inserts all kinds of
funny codes, that makes your text hard to read.)

   I have a paradox I cannot understand. I have compiled a program under
   GCC and under Borland TC (v. 2.0) and TC++ (v. 3.1) for Windows,
   and both versions give results quite different, being the GCC version
   the correct one. I include a simple code that represent the simplifie=
   d
   core of the problem: a double obtained from a product and stored subt=
   racted
   =66rom the same product does not give 0 as result. It seems an error =
   of
   Borland compilers but I feel it to serious to be true; I'd like to kn=
   ow
   if it is a real bug or if it has some justification (although the res=
   ult
   is erroneus) and if there is some way to skip the error without affec=
   ting
   the code performace.

This is a feature, not a bug :-)

Seriously, compilers are allowed to work with higher precision
for temporary results than for values stored in `double'
variables.  The compiler just differ in their oppinion of
`temporary'.

Morten
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-------------------------------------------Morten Welinder, terra AT diku DOT dk