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From: jsa@alexandria (Jon S Anthony)
Subject: Re: Ada95 to ANSI_C converter
Date: 1997/04/04
Message-ID: <JSA.97Apr3191910@alexandria>#1/1
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Distribution: world
References: <5hbrah$ctt$1@gail.ripco.com> <JSA.97Apr2144544@alexandria>
Organization: PSI Public Usenet Link
Newsgroups: comp.lang.ada
Date: 1997-04-04T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <E831sB.M4s@world.std.com> bobduff@world.std.com (Robert A Duff) writes:

> >> <<So, were these tricks still captured in generated C or were they
> >> something else?  If they were still captured in the generated C, then
> >> it would seem that the use of the term "fundamentally" here is not
> >> quite accurate.  I mean, the ICC work would be an existence proof to
> >> the contrary.>>
> 
> I'm not sure what you're asking.  My belief (from vague memories of a
> Dan Eilers post) is that they did something different for different
> targets, to support "efficient" trapping of overflows.  I don't know
> whether it was different generated C code, or different libraries, or
> what.  I've never actually used the thing, myself -- just vague
> memories of postings.

OK, this is certainly an answer to the question - you aren't sure how
the tricks were done.  Basically I just was wondering if the "tricks"
were implemented via generated C (then assuming they really were
efficient, then the ICC impl would be something of a counter example -
at least for overflow stuff).


> Particular implementations of C might be able to.  So there's something
> "fundamental" about this inefficiency, if we're talking about standard,
> portable C.                                                   ^^^^^^^^
  ^^^^^^^^^^

OK, check.


> This is just one issue.  How do you implement the "raise" statement
> in standard C.  Well, most C programmers return status codes, or
> whatever, which is, I think, fundamentally less efficient than real
> exception handling supported by a run-time system.  If you're
> willing to take advantage of a particular C implementation's stack
> layout, then you might be able to gain efficiency.  But in standard
> C, I don't see how to implement the typical "near-zero overhead" for
> entering the region of an exception handler.

OK, you convinced me.


> Well, I didn't really understand the question, so I'm not surprised
> Robert didn't, either.

Managed to answer it though! :-)

/Jon
-- 
Jon Anthony
Organon Motives, Inc.
Belmont, MA 02178
617.484.3383
jsa@organon.com