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NNTP-Posting-Date: Sat, 08 Dec 2007 19:45:53 -0600
From: tmoran@acm.org
Newsgroups: comp.lang.ada
Subject: Re: GNAT.Sockets: Timeval_Duration is in milliseconds?
References: <99906a58-2645-4880-bd13-9b63a30ffb59@e4g2000hsg.googlegroups.com>
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Date: 2007-12-08T19:45:53-06:00
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> But that was precisely my point to rather make a new type instead of
> subtyping, since scales are totally different.  But that is subjective
> I guess.

  The Ada 95 LRM 9.6(7) says
"...; a value of type Duration is used to represent the length of
an interval of time, expressed in seconds."

It would be bad practice to use a value of type Duration to represent,
say, the number of gallons of gasoline remaining, and it would be even
worse, because even more confusing, to use it to represent a number
of milliseconds.

>>    Forever   : constant := Duration (Integer'Last) * 1.0;
Is that legal Ada?

Something like
   Forever : constant := Integer'last * 1.0;
or
   Forever : constant Duration := Integer'last * 1.0;
or
   Forever : constant Duration := Duration(Integer'last);
would seem preferable.

(It should probably use Interfaces.C.Int'Last instead of Integer'Last,
and if Interfaces.C.Int is 64 bits that would probably give a compile
time warning.)

>    --  Timeval_Duration is a subtype of Standard.Duration because the full
>    --  range of Standard.Duration cannot be represented in the equivalent C
>    --  structure.
>...
>    Forever   : constant := Duration (Integer'Last) * 1.0;
>
>    subtype Timeval_Duration is Duration range Immediate .. Forever;

If the code is going to multiply by 1000 to convert milliseconds to integers
to put into the C structure, then of course it should be
     Forever : constant Duration := Duration(Integer'last)/1000;