From: Keith Thompson <kst-u@mib.org>
Subject: Re: Fixed point constants issue
Date: Tue, 14 Sep 2010 12:44:29 -0700
Date: 2010-09-14T12:44:29-07:00 [thread overview]
Message-ID: <lnk4mof6ua.fsf@nuthaus.mib.org> (raw)
In-Reply-To: 1f0l0baynq1x7$.phl9cqpwcr37.dlg@40tude.net
"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
> On Mon, 13 Sep 2010 19:27:30 +0200, Vinzent Hoefler wrote:
>> Is this a GNAT bug or am I just stupid?
>>
>> Suppose we have a fixed point type (with a rather large delta):
>>
>> -- 8< --
>> with Ada.Text_IO; use Ada.Text_IO;
>>
>> procedure Fixed_Point
>> is
>> FEET_PER_METER : constant := 0.3048;
>> HEIGHT : constant := 10; -- Feet
>>
>> type Altitude is delta (2.0**15 / 50_000.0) range 0.0 .. 50_000.0;
>
> [...]
>> Can anyone shed some light on this? This has driven us crazy for weeks now.
>>
>> [1] Of course, "Altitude'(HEIGHT * FEET_PER_METER)" yields "0.0" again.
>> At least this is consistent with my understanding so far.
>
> Hmm, what did you expect? 0.3048 (FEET_PER_METER) is 0 when Altitude. That
> is because 2.0**15/50_000.0=0.65536 > 0.3048.
Close, but actually it's because 2.0**15/50_000.0=0.65536 > 0.5.
Altitude'Delta = 0.65536. Altitude'Small = 0.5. If you want the
'Small to be the same as the 'Delta, you have to specify it (or
use a power of 2.0).
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
prev parent reply other threads:[~2010-09-14 19:44 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-13 17:27 Fixed point constants issue Vinzent Hoefler
2010-09-13 18:04 ` Dmitry A. Kazakov
2010-09-13 18:25 ` Vinzent Hoefler
2010-09-13 19:05 ` Niklas Holsti
2010-09-13 20:35 ` Vinzent Hoefler
2010-09-13 20:35 ` Jeffrey Carter
2010-09-13 21:06 ` Vinzent Hoefler
2010-09-14 5:39 ` Niklas Holsti
2010-09-24 14:43 ` Markus Schöpflin
2010-09-24 20:05 ` Vinzent Hoefler
2010-09-24 21:38 ` Jeffrey Carter
2010-09-24 22:42 ` Vinzent Hoefler
2010-09-25 0:16 ` Jeffrey Carter
2010-09-27 10:33 ` Markus Schöpflin
2010-09-27 18:57 ` Jeffrey Carter
2010-09-28 8:16 ` Markus Schöpflin
2010-09-28 17:28 ` Jeffrey Carter
2010-10-05 6:27 ` Randy Brukardt
2010-10-05 18:40 ` Jeffrey Carter
2010-09-27 17:58 ` Adam Beneschan
2010-09-13 20:32 ` Dmitry A. Kazakov
2010-09-13 21:08 ` Vinzent Hoefler
2010-09-14 6:54 ` J-P. Rosen
2010-09-14 18:28 ` Vinzent Hoefler
2010-09-14 7:47 ` Dmitry A. Kazakov
2010-09-14 17:42 ` Vinzent Hoefler
2010-09-15 8:35 ` Dmitry A. Kazakov
2010-09-15 17:24 ` Vinzent Hoefler
2010-09-15 20:11 ` Dmitry A. Kazakov
2010-09-14 19:44 ` Keith Thompson [this message]
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