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From: Dirk Herrmann <fight_spam@invalid.invalid>
Newsgroups: comp.lang.ada
Subject: Re: conversions between fixed-point types
Date: Sat, 26 Sep 2009 16:43:22 +0200
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Stuart wrote:
> Having played with this on GNATPro 6.1.2 (to PC target) it does report 
> FpB'Machine_Rounds as false.  It also rounds values like -1.59999 down to
> -1.2 (which is a logical consequence).  Technically this is still within the 
> error bounds declared for FpB (delta 0.4) so it is not "wrong" within the 
> rules of the language definition.  But it is very counter-intuitive and is 
> the sort of thing I find frustrating.
> 
> I also tested the problem on GreenHills AdaMULTI (4.2.3 to PowerPC target); 
> this gave FpB'Machine_Rounds as true and gave the more intuitive results.
> 
>    -1.5         -> -1.6
>    -1.40001 -> -1.6
>    -1.4         -> -1.2
> 
> So although there does look to be a language "gotcha" here, it depends upon 
> the compiler's choice of 'Machine_Rounds.

Whom could I contact to figure out whether this is an omission in the language 
definition (which could then be fixed) or whether it is intentional?  I would 
also like to ask about another issue:

Dirk Herrmann wrote:
 > Robert A Duff wrote:
 >> By the way, you can say:
 >>
 >>     for T'Small use T'Delta;
 >>
 >> to avoid repeating yourself.
 >
 > I have tried that, especially since the very same recommendation was
 > given in the Barnes book "Ada 2005".  But, GNAT gives an error message.
 > It seems that the very moment you reference T'Delta the type T gets
 > "frozen" such that  the "use" statement itself freezes T before it can
 > modify it.  I don't know if this is what the authors of the reference
 > manual had intended, but GNAT interprets it that way.

--
Dirk