From: stt@houdini.camb.inmet.com (Tucker Taft)
Subject: Re: Boolean Representation
Date: 1998/09/25
Date: 1998-09-25T00:00:00+00:00 [thread overview]
Message-ID: <EzuGHH.C6E.0.-s@inmet.camb.inmet.com> (raw)
In-Reply-To: 6udkck$87k$1@nnrp1.dejanews.com
matthew_snyder@my-dejanews.com wrote:
: Is it safe to assume that a boolean value of FALSE is always internally
: represented as 0 and TRUE is represented as 1 for most Ada compilers? Will
: the results of an unchecked conversion from a boolean to an integer be
: consistent for different compilers?
To answer your original question:
The answer is "no." Boolean is the only enumeration
type where the "default" representation need not start at 0
and go up by consecutive integers.
We argued a bit over this during the Ada 9X design process. We
agreed that all user-defined enumeration types should be guaranteed
a default representation that was 0-based. However, there was
existing hardware for which 0,16#FFFF_FFFF# was a better
representation to use for boolean (due to the set-zero/set-ones
instructions, e.g. on the 68K). Furthermore, some existing
Ada 83 compilers took advantage of this.
See RM95 13.4(8), and AARM 13.4(8a,8b).
: Matt Snyder
: matthew_snyder@hotmail.com
--
-Tucker Taft stt@inmet.com http://www.inmet.com/~stt/
Intermetrics, Inc. Burlington, MA USA
An AverStar Company
next prev parent reply other threads:[~1998-09-25 0:00 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
1998-09-24 0:00 Boolean Representation matthew_snyder
1998-09-25 0:00 ` Tucker Taft [this message]
1998-09-25 0:00 ` dewarr
1998-09-25 0:00 ` dewarr
-- strict thread matches above, loose matches on Subject: below --
1998-09-24 0:00 matthew_snyder
1998-09-24 0:00 ` dennison
1998-09-24 0:00 ` Keith Thompson
1998-09-25 0:00 ` dennison
1998-09-25 0:00 ` Keith Thompson
1998-09-26 0:00 ` Tucker Taft
1998-09-26 0:00 ` Keith Thompson
1998-09-27 0:00 ` dewarr
1998-09-27 0:00 ` dewarr
1998-09-24 0:00 ` dewarr
1998-09-24 0:00 ` Samuel T. Harris
1998-09-25 0:00 ` dewarr
1998-09-27 0:00 ` Samuel T. Harris
1998-09-28 0:00 ` dewar
1998-09-24 0:00 ` matthew_snyder
1998-09-24 0:00 ` Tom Moran
1998-09-25 0:00 ` dewarr
1998-09-25 0:00 ` Tom Moran
1998-09-24 0:00 ` dennison
1998-09-25 0:00 ` dewarr
1998-09-25 0:00 ` Robert I. Eachus
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