Re: Ada 95 Numerics questions for the experts

[stt@houdini.camb.inmet.com (Tucker Taft)]

Robert Dewar (dewar@merv.cs.nyu.edu) wrote:

: <<Nope. The AdaMajic front end (Green hills in this case) rounds the
: components to 8 bits even in the precense of a pragma pack
: you get a 64 Byte array.>>

: SOunds like a bug to me, since these compilers say they support
: annex C, this means that the implementation advice in chapter 13 (13.2(9))
: ...

Sounds like a misconception to me.  The compiler supports packing to
the bit level.  It would be helpful if the actual source code that
illustrated the problem were posted, because we have never had
a bug report relating to an inability to pack.

As far as packing to an array of 3-bits per element versus 4-bits per
element, we have generally chosen to follow the recommendations of the
RM.  Going beyond the RM is not always in the customer's interest,
as they may have to move to another Ada compiler at some point, and
one of the goals of standardization is portability between implementations.

For example, we used to support very long source lines, though the actual
limit was a bit hard to define.  We now support exactly 200 as the maximum
length of a line (which is the length guaranteed by the RM), because 
supporting something like 256 or some other number chosen by us did not 
seem to be doing the customer a great favor.

Of course, if a customer was willing to pay extra to get tighter packing, 
perhaps in the presence of some special pragma Jam_Packed(xxx), we would be
happy to accommodate them (I think this general "disclaimer" applies
to ACT as well ;-).  However, as mentioned above, we have currently 
chosen to follow the RM recommendations as closely as possible for
the "standard" pragma Pack, and if you find that we don't, please 
file a bug report.

--
-Tucker Taft   stt@inmet.com   http://www.inmet.com/~stt/
Intermetrics, Inc.  Burlington, MA  USA

P.S. By the way, on our 24-bit-per-storage-unit target, we pack arrays
to element sizes of 1, 2, 3, 4, 6, 8, and 12.  I remember someone
once arguing for a word size of 72 bits on the grounds that it had
a lot of factors ;-).