LISTSERV mailing list manager LISTSERV 16.0

Help for TEAM-ADA Archives


TEAM-ADA Archives

TEAM-ADA Archives


TEAM-ADA@LISTSERV.ACM.ORG


View:

Message:

[

First

|

Previous

|

Next

|

Last

]

By Topic:

[

First

|

Previous

|

Next

|

Last

]

By Author:

[

First

|

Previous

|

Next

|

Last

]

Font:

Proportional Font

LISTSERV Archives

LISTSERV Archives

TEAM-ADA Home

TEAM-ADA Home

TEAM-ADA  October 1998

TEAM-ADA October 1998

Subject:

Did I get this right?

From:

"W. Wesley Groleau x4923" <[log in to unmask]>

Reply-To:

W. Wesley Groleau x4923

Date:

Mon, 19 Oct 1998 08:59:02 -0500

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (80 lines)

I met a guy who is definitely anti-Ada and pro-C.  Unfortunately, he is
now a support person for an Ada vendor.  Recently he responded to a bug
report as follows:

  I have researched this problem and find that the designers of the Ada
  language changed the meaning of the Size attribute.  Basically, the
  difference is that Ada 83 gave you the size of the storage container and
  Ada 95 gives you the size of the bits of actual interest.  As what is
  normally wanted for programming purposes is the number of bytes, the Ada
  83 construction X'Size/8 was just fine.  To get the same result in Ada
  95, what is wanted is (X'Size+7)/8.  For any customer converting from
  Ada 83 to Ada 95, this is a problem because it shows up in small print
  in the middle of hundreds of pages that only a compiler-writer could
  love.

  We can argue about the poor form of the Ada 95 designers to change the
  meaning of something, essentially postponing error detection to runtime,
  but the solution is simple. Any project converting from Ada 83 to Ada 95
  should grep over their source tree and examine any uses of 'Size.

  I do not anticipate any change to alleviate the impact of the language
  designers decision.  The only change I believe we might see, not in a
  short timeframe, would be to add a [vendor-specific] attribute something
  like X'Size83.  Either way, source code would need to be examined and
  changed.

MY RESPONSE:

  I'm sorry, but this is only partly true.

  Ada '83: "X'SIZE  Applied to an object, yields the number of bits
  allocated to hold the object. ..."

   Ada '95: "X'Size   Denotes the size in bits of the representation of
  the object."

  In Ada Issue AI-00536, the Ada '83 language was clarified with a binding
  interpretation that said (among other things): "...This number may
  include padding bits that are part of the stored value....For the
  predefined type Boolean, BOOLEAN'SIZE is one.  An implementation shall
  describe, in Appendix F, how the value of 'SIZE is determined...."

  I suspect that the "may" was put in to warn users of how compiler
  vendors had misinterpreted the intent.  Too late to close the door, just
  let everyone know the cows are out.

  In Ada '95, the language was made a little more precise but the meaning
  (of the original intent) was not changed.  In my opinion, eliminating
  portability problems that were never intended to occur was not "poor
  form." Poor form is accusing them of moving an error detection from
  compile-time to run-time when one of the general goals of the revision
  was the opposite.  The truth is, Rational now detects an error at
  run-time that was not detected at all before.

  The real problem is that Object'Size/8 was never the correct way to find
  the number of octets an object had bits in.  In all dialects of Ada,
  integer division truncates.  Therefore:

  Object'Size    Object'Size/8  (Object'Size+7)/8
       1                0                 1
       5                0                 1
       7                0                 1
       8                1                 1
       9                1                 2

  So we were just lucky in the past that Rational (probably
  unintentionally) took advantage of looseness in the definition of Ada
  and in the process, compensated for our coding error.

  I do agree with [his] recommendation:  We should search our code for
  other instances of this error, and correct them.

   Ada is not perfect.  The designers and reviewers of Ada '95 are human,
  therefore must have made mistakes.  A very few of those mistakes are
  still in the language---this is not one of them.  We should just be glad
  that 95-99% of the mistakes were discovered by expert reviewers (instead
  of by the users, as with today's three most popular languages).

DID MY RESPONSE MISINTERPRET ANYTHING?

Top of Message | Previous Page | Permalink

Advanced Options


Options

Log In

Log In

Get Password

Get Password


Search Archives

Search Archives


Subscribe or Unsubscribe

Subscribe or Unsubscribe


Archives

December 2017
November 2017
October 2017
September 2017
June 2017
May 2017
April 2017
January 2017
December 2016
November 2016
October 2016
August 2016
July 2016
June 2016
May 2016
April 2016
March 2016
February 2016
January 2016
December 2015
November 2015
October 2015
September 2015
August 2015
June 2015
May 2015
April 2015
March 2015
February 2015
January 2015
December 2014
November 2014
September 2014
August 2014
July 2014
June 2014
May 2014
April 2014
March 2014
February 2014
January 2014
December 2013
November 2013
October 2013
September 2013
June 2013
May 2013
April 2013
March 2013
February 2013
January 2013
December 2012
November 2012
October 2012
September 2012
August 2012
July 2012
June 2012
May 2012
April 2012
February 2012
January 2012
December 2011
November 2011
October 2011
September 2011
August 2011
July 2011
June 2011
May 2011
April 2011
December 2010
November 2010
October 2010
September 2010
June 2010
May 2010
April 2010
March 2010
February 2010
January 2010
December 2009
November 2009
October 2009
September 2009
August 2009
July 2009
June 2009
May 2009
April 2009
February 2009
January 2009
December 2008
November 2008
October 2008
September 2008
August 2008
June 2008
May 2008
April 2008
March 2008
February 2008
January 2008
December 2007
November 2007
October 2007
September 2007
June 2007
May 2007
March 2007
February 2007
December 2006
November 2006
October 2006
September 2006
August 2006
July 2006
June 2006
May 2006
April 2006
March 2006
February 2006
January 2006
December 2005
November 2005
October 2005
August 2005
July 2005
June 2005
May 2005
April 2005
March 2005
February 2005
January 2005
December 2004
November 2004
October 2004
September 2004
August 2004
July 2004
June 2004
May 2004
March 2004
February 2004
January 2004
December 2003
November 2003
October 2003
September 2003
August 2003
July 2003
June 2003
May 2003
April 2003
March 2003
February 2003
January 2003
December 2002
November 2002
October 2002
September 2002
August 2002
July 2002
June 2002
May 2002
April 2002
March 2002
February 2002
December 2001
November 2001
October 2001
September 2001
August 2001
July 2001
June 2001
May 2001
April 2001
March 2001
February 2001
January 2001
December 2000
November 2000
October 2000
September 2000
August 2000
July 2000
June 2000
May 2000
April 2000
March 2000
February 2000
January 2000
December 1999
November 1999
October 1999
September 1999
August 1999
July 1999
June 1999
May 1999
April 1999
March 1999
February 1999
January 1999
December 1998
November 1998
October 1998
September 1998
August 1998
July 1998
June 1998
May 1998
April 1998
March 1998
February 1998
January 1998
December 1997
November 1997
October 1997
September 1997
August 1997
July 1997
June 1997
May 1997
April 1997
March 1997
February 1997
January 1997
December 1996
November 1996
October 1996

ATOM RSS1 RSS2



LISTSERV.ACM.ORG

Secured by F-Secure Anti-Virus CataList Email List Search Powered by the LISTSERV Email List Manager