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From: Samuel Tardieu <sam@rfc1149.net>
Newsgroups: comp.lang.ada
Subject: Re: Negative float problem
References: <1130351574.313991.229420@g14g2000cwa.googlegroups.com>
Date: 26 Oct 2005 21:05:42 +0200
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Date: 2005-10-26T21:06:00+02:00
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>>>>> "Luke" == Luke  <lukeedw@hotmail.com> writes:

Luke> If 2 works then why doesnt the original?  The same is true for
Luke> +1.0.  Is this a fault with gcc?

No.

In your first attempt

  X : file1.My_Float := -1.0;

you are trying to use the "-" operator on the My_Float type. The
operator is not immediately visible as it is defined in the file1
package.

In the second attempt

  X : file1.My_Float := file1.My_Float (-1.0);

you are in fact converting the Universal_Float value "-1.0" (which is
obtained after having applied the unary "-" operator on the
Universal_Float value "1.0", and this operator is always visible) to
type My_Float.

In fact, it is equivalent to writing

  Y : constant := -1.0;
  X : file1.My_Float := Y;

If you look at Ada95 grammar (in Annex P if I remember correctly), you
will see that numbers are defined *without* any leading "+" and "-"
signs. Each time you write "-xxx", you apply the unary "-" operator to
"xxx".

Note that you could have written also

  X : file1.My_Float := file1."-" (1.0);

I think that almost any Ada-er has learnt this rule the hard way one
day or another :)

  Sam
-- 
Samuel Tardieu -- sam@rfc1149.net -- http://www.rfc1149.net/sam