Re: Static vs dynamic evaluation anomaly?

["Jeffrey R. Carter" <jrcarter@acm.org>]

Adam Beneschan wrote:
> 
> Seems like a pretty lame excuse, though.  Ada does have a Suppress
> pragma to suppress checks; as I understand the documentation, omitting
> -gnato causes certain checks not to be performed, and using -gnatp
> causes even more checks not to be performed, so the result should be
> more or less equivalent to using Suppress.  So it probably isn't
> accurate to say that GNAT isn't Ada in that case, but that's perhaps a
> matter of semantics.  In any case, though, using Suppress, or not
> using -gnato, or using -gnatp, shouldn't produce *different* results.
> The most I would expect is that the behavior would be different in
> cases where an exception would be raised if the check were performed---
> but I would not expect different behavior in a case where *no*
> exception is raised.  And in this case, no exception is raised---the
> Put is outputting different values.  So I still think this is a bug
> that needs to be fixed.  The current behavior (assuming that 4.1.1-22
> behaves the same as 4.0.0) isn't reasonable.

What's happening (I think) is the base type is 8 bits. Without -gnato, 
there's no check to see if the result exceeds this and should be reduced 
mod the modulus, so an out-of-range value is produced. The output is 
always outputting an 8-bit value; with the check, this value always fits 
in 6 bits; without it, it may be larger.

This may well be an error, possibly with Modular_IO.

-- 
Jeff Carter
"It's all right, Taggart. Just a man and a horse being hung out there."
Blazing Saddles
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