Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.c > #98346

Re: "Lete2??s Stop Bashing C"

From David Brown <david.brown@hesbynett.no>
Newsgroups comp.lang.c
Subject Re: "Lete2??s Stop Bashing C"
Date 2016-12-08 10:24 +0100
Organization A noiseless patient Spider
Message-ID <o2b8ql$bhk$1@dont-email.me> (permalink)
References (11 earlier) <o28p9e$lhj$2@dont-email.me> <87fum0ezb6.fsf@bsb.me.uk> <o28u0n$4v8$2@dont-email.me> <o2a3bg$cf6$1@dont-email.me> <o2a5ha$mb5$1@dont-email.me>

Show all headers | View raw

On 08/12/16 00:22, jacobnavia wrote:
>>> I think Jacob may not understand what "regular" means. Jacob, a
>>> "regular" is someone who posts many articles over a lengthy period of
>>> time. That includes you, Jacob. You /are/ a regular.
>>>
>>
> 
> Look guys, I am repeating what I said six and half years ago and it is
> distressing that all the refuted arguments come again as nothing ever
> would move in this group.
> 
> 1) You all know very well what I mean when I say that C has weakness
> that should be adressed. In my discussion I present technical arguments
> that are not refuted.
> 
> 2) All machines can check for overflow. For instance, Mr Brown proposed
> for MIPS:
> 
> #addition...
> addu $t0, $t1, $t2 # caution, don't trap!
> xor  $t3, $t1, $t2 # if signs differ $t3 < 0
> slt  $t3, $t3, $zero
> bne $t3, $zero, No_overflow #signs differ
> xor $t3,$t0,$t1 # signs match, check result
> slt $t3,$t3,$zero #sum sign different
> bne $t3,$zero, Overflow..
> 
> That's when you buy a machine like that... Others are better, as
> everybody knows. Some machines do not have flags to test but any
> overflow is rerouted to an interrupt routine that probably the software
> can adapt. It is maybe expensive but the language should provide means
> of doing that fairly easily, by default if you want.
> 
> Any overflow is a signal that is rerouted to code to treat an overflow
> condition. You can assign priorities to pieces of the software, meaning
> that if an overflow occurs because of data noise, or electrical
> problems, or just variables that weren't sized correctly there is a
> "restart" point for that module.
> 
> C allows for a standard way of treating floating point overflow but not
> integer overflow. This is no longer justified.
> 
> Now, how could that be done?
> 
> Let's discuss that for once?
> 
> OK?
> 

Don't you also want to ask if it /should/ be done?  I think in many
cases there is no need to have overflow checking in floating point
either - especially as the ability to check for overflow can be
extremely costly.  In particular, if you have overflow checking (for
integer or floating point) you hinder a lot of compiler optimisation
such as re-arrangement of expressions, as your operations are no longer
commutable, associative, and otherwise mathematically "nice".  And when
dealing with "big" processors, overflow checking means you can't do
things in parallel using SIMD or vector instructions.

I agree that overflow checking can sometimes be useful for testing and
debugging.  If you want to implement it, there are various methods:

1. Make it machine-dependent and have a way to check for an "overflow
flag" after an operation.  This only makes sense on processors that
actually have an overflow flag.  It is also, IMHO, a poor solution.  It
gets really messy for expressions of more than one part - how is the
flag set in "(a + b) * (c + d)" ?  The user pays a high price in weak
code generation even when he knows there is no overflow.

2. Make it machine-dependent and support trap-on-overflow when
supported.  This has low cost to the user - the only limitation is to
prevent optimisations and code re-arrangement.  You get a "crash to
debugger" when overflow happens, which can be very helpful in tracing bugs.

3. Make it explicit in the code, such as is done with gcc's
__builtin_add_overflow extension.  Users can check for overflow as
needed.  The compiler can generate tight code (using the overflow flag
if supported, or weird sequences like the MIPS one above - there is
always a way).  That keeps everything explicit, has minimal overhead,
and lets user code handle overflow at run-time.  But it's ugly in the
user code.  (Special types and operator overloading compiler extensions
might let you do this in a neater way.)

4. Implement some sort of exception mechanism, and special types or
classes of integers for which overflow checking is enabled.  This has
the advantage of being implementable as classes in existing C++ without
changes to the compiler.  The disadvantage, of course, is that it is C++
and not C.

5. I expect there are more ideas ...

Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

"Let’s Stop Bashing C" Lynn McGuire <lynnmcguire5@gmail.com> - 2016-12-05 19:57 -0600
  Re: "Let’s Stop Bashing C" Richard Heathfield <rjh@cpax.org.uk> - 2016-12-06 02:34 +0000
    Re: "Let’s Stop Bashing C" BGB <cr88192@hotmail.com> - 2016-12-06 00:13 -0600
      Re: "Let’s Stop Bashing C" BartC <bc@freeuk.com> - 2016-12-06 23:15 +0000
        Re: "Let’s Stop Bashing C" BGB <cr88192@hotmail.com> - 2016-12-06 21:16 -0600
    Re: "Let’s Stop Bashing C" Richard Heathfield <rjh@cpax.org.uk> - 2016-12-06 11:54 +0000
    Re: "Let’s Stop Bashing C" BartC <bc@freeuk.com> - 2016-12-06 12:07 +0000
      Re: "Let’s Stop Bashing C" Richard Heathfield <rjh@cpax.org.uk> - 2016-12-06 12:25 +0000
        Re: "Let’s Stop Bashing C" David Brown <david.brown@hesbynett.no> - 2016-12-06 14:07 +0100
          Re: "Let’s Stop Bashing C" Richard Heathfield <rjh@cpax.org.uk> - 2016-12-06 13:40 +0000
        Re: "Let’s Stop Bashing C" jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-06 19:40 +0100
          Re: "Lete2��s Stop Bashing C" Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2016-12-06 13:55 -0500
            Re: "Lete2��s Stop Bashing C" Richard Heathfield <rjh@cpax.org.uk> - 2016-12-06 19:13 +0000
              Re: "Lete2��s Stop Bashing C" Keith Thompson <kst-u@mib.org> - 2016-12-06 11:51 -0800
                Re: "Lete2��s Stop Bashing C" supercat@casperkitty.com - 2016-12-06 12:22 -0800
            Re: "Lete2��s Stop Bashing C" jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-06 20:16 +0100
            Re: "Lete2�™s Stop Bashing C" supercat@casperkitty.com - 2016-12-06 11:20 -0800
              Re: "Lete2�™s Stop Bashing C" jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-06 22:15 +0100
                Re: "Lete2�™s Stop Bashing C" Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2016-12-06 16:49 -0500
                Re: "Lete2�™s Stop Bashing C" supercat@casperkitty.com - 2016-12-06 14:24 -0800
                Re: "Lete2�™s Stop Bashing C" jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-07 00:07 +0100
                Re: micro-architectural details Noob <root@127.0.0.1> - 2016-12-07 22:04 +0100
                Re: micro-architectural details jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-07 23:44 +0100
                Re: micro-architectural details BartC <bc@freeuk.com> - 2016-12-07 23:02 +0000
                Re: micro-architectural details Keith Thompson <kst-u@mib.org> - 2016-12-07 15:28 -0800
                Re: micro-architectural details Noob <root@127.0.0.1> - 2016-12-08 21:36 +0100
                Re: micro-architectural details supercat@casperkitty.com - 2016-12-08 12:56 -0800
                Re: micro-architectural details Noob <root@127.0.0.1> - 2016-12-08 23:03 +0100
                Re: micro-architectural details supercat@casperkitty.com - 2016-12-08 14:21 -0800
                Re: micro-architectural details Noob <root@127.0.0.1> - 2016-12-08 23:36 +0100
                Re: micro-architectural details BartC <bc@freeuk.com> - 2016-12-08 21:59 +0000
                Re: micro-architectural details Noob <root@127.0.0.1> - 2016-12-08 23:25 +0100
                Re: micro-architectural details supercat@casperkitty.com - 2016-12-08 14:34 -0800
                Re: micro-architectural details Noob <root@127.0.0.1> - 2016-12-08 23:59 +0100
                Re: micro-architectural details Melzzzzz <mel@zzzzz.com> - 2016-12-09 00:18 +0100
                Re: micro-architectural details fir <profesor.fir@gmail.com> - 2016-12-09 00:06 -0800
                Re: micro-architectural details jt@toerring.de (Jens Thoms Toerring) - 2016-12-09 11:35 +0000
                Re: micro-architectural details BartC <bc@freeuk.com> - 2016-12-09 12:12 +0000
                Re: micro-architectural details David Brown <david.brown@hesbynett.no> - 2016-12-09 13:33 +0100
                Re: micro-architectural details Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-12-09 15:41 -0800
                Re: micro-architectural details Tim Rentsch <txr@alumni.caltech.edu> - 2016-12-10 09:28 -0800
                Re: micro-architectural details supercat@casperkitty.com - 2016-12-10 09:58 -0800
                Re: micro-architectural details Tim Rentsch <txr@alumni.caltech.edu> - 2016-12-14 22:53 -0800
                Re: micro-architectural details Robert Wessel <robertwessel2@yahoo.com> - 2016-12-11 03:10 -0600
                Re: micro-architectural details jt@toerring.de (Jens Thoms Toerring) - 2016-12-11 13:48 +0000
                Re: micro-architectural details BartC <bc@freeuk.com> - 2016-12-11 14:43 +0000
                Re: micro-architectural details Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-11 16:23 +0000
                Re: micro-architectural details Keith Thompson <kst-u@mib.org> - 2016-12-11 12:53 -0800
                Re: micro-architectural details Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-11 21:27 +0000
                Re: micro-architectural details supercat@casperkitty.com - 2016-12-11 08:46 -0800
                Re: micro-architectural details Tim Rentsch <txr@alumni.caltech.edu> - 2016-12-14 21:14 -0800
                Re: micro-architectural details supercat@casperkitty.com - 2016-12-15 08:25 -0800
                Re: micro-architectural details Tim Rentsch <txr@alumni.caltech.edu> - 2016-12-14 21:11 -0800
                Re: micro-architectural details BartC <bc@freeuk.com> - 2016-12-15 14:28 +0000
                Re: micro-architectural details David Brown <david.brown@hesbynett.no> - 2016-12-11 18:38 +0100
                Re: micro-architectural details Tim Rentsch <txr@alumni.caltech.edu> - 2016-12-15 00:25 -0800
                Re: micro-architectural details supercat@casperkitty.com - 2016-12-09 07:42 -0800
                Re: micro-architectural details Keith Thompson <kst-u@mib.org> - 2016-12-09 11:54 -0800
                Re: micro-architectural details David Brown <david.brown@hesbynett.no> - 2016-12-09 10:27 +0100
                Re: other missing features (no-brainers) Noob <root@127.0.0.1> - 2016-12-09 17:05 +0100
                Re: micro-architectural details jt@toerring.de (Jens Thoms Toerring) - 2016-12-09 09:51 +0000
                Re: "Lete2�™s Stop Bashing C" Jerry Stuckle <jstucklex@attglobal.net> - 2016-12-06 20:42 -0500
                Re: "Lete2�™s Stop Bashing C" supercat@casperkitty.com - 2016-12-06 14:16 -0800
                Re: "Lete2�™s Stop Bashing C" jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-07 00:31 +0100
                Re: "Let's Stop Bashing C" Keith Thompson <kst-u@mib.org> - 2016-12-06 15:55 -0800
                Re: "Let's Stop Bashing C" jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-07 01:01 +0100
                Re: "Lete2�™s Stop Bashing C" supercat@casperkitty.com - 2016-12-06 16:42 -0800
                Re: "Lete2�™s Stop Bashing C" jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-07 01:55 +0100
                Re: "Lete2�™s Stop Bashing C" supercat@casperkitty.com - 2016-12-07 07:11 -0800
                Re: "Lete2??s Stop Bashing C" Ike Naar <ike@iceland.freeshell.org> - 2016-12-06 23:05 +0000
                Re: "Lete2??s Stop Bashing C" jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-07 00:43 +0100
                Re: "Lete2??s Stop Bashing C" Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-07 03:06 +0000
                Re: "Lete2??s Stop Bashing C" jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-07 11:47 +0100
                Re: "Lete2??s Stop Bashing C" Thiago Adams <thiago.adams@gmail.com> - 2016-12-07 03:10 -0800
                Re: "Lete2??s Stop Bashing C" Thiago Adams <thiago.adams@gmail.com> - 2016-12-07 03:13 -0800
                Re: "Lete2??s Stop Bashing C" Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-07 11:47 +0000
                Re: "Lete2??s Stop Bashing C" Richard Heathfield <rjh@cpax.org.uk> - 2016-12-07 12:08 +0000
                Re: "Lete2??s Stop Bashing C" David Brown <david.brown@hesbynett.no> - 2016-12-07 23:45 +0100
                Re: "Lete2??s Stop Bashing C" jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-08 00:22 +0100
                Re: "Lete2??s Stop Bashing C" Keith Thompson <kst-u@mib.org> - 2016-12-07 15:32 -0800
                Re: "Let's Stop Bashing C" jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-08 01:25 +0100
                Re: "Let's Stop Bashing C" supercat@casperkitty.com - 2016-12-07 16:36 -0800
                Re: "Let's Stop Bashing C" Keith Thompson <kst-u@mib.org> - 2016-12-07 17:09 -0800
                Re: "Let's Stop Bashing C" jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-08 10:28 +0100
                Re: "Let's Stop Bashing C" Keith Thompson <kst-u@mib.org> - 2016-12-08 08:34 -0800
                Re: "Let's Stop Bashing C" Gareth Owen <gwowen@gmail.com> - 2016-12-08 20:08 +0000
                Re: "Lete2??s Stop Bashing C" David Brown <david.brown@hesbynett.no> - 2016-12-08 10:24 +0100
                Re: "Lete2??s Stop Bashing C" jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-08 15:49 +0100
                Re: "Lete2??s Stop Bashing C" Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-08 15:23 +0000
                Re: "Lete2??s Stop Bashing C" jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-08 16:58 +0100
                Re: "Lete2??s Stop Bashing C" Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-08 18:57 +0000
                Re: "Lete2??s Stop Bashing C" Richard Heathfield <rjh@cpax.org.uk> - 2016-12-08 15:29 +0000
                Re: "Lete2??s Stop Bashing C" jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-08 17:09 +0100
                Re: "Lete2??s Stop Bashing C" Richard Heathfield <rjh@cpax.org.uk> - 2016-12-08 16:41 +0000
                Re: "Lete2??s Stop Bashing C" David Brown <david.brown@hesbynett.no> - 2016-12-08 17:04 +0100
                Re: "Lete2??s Stop Bashing C" jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-08 17:15 +0100
                Re: "Lete2??s Stop Bashing C" Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2016-12-08 11:34 -0500
                Re: "Lete2??s Stop Bashing C" jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-08 18:40 +0100
                Re: "Lete2??s Stop Bashing C" supercat@casperkitty.com - 2016-12-08 10:00 -0800
                Re: "Lete2??s Stop Bashing C" Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-12-08 19:05 +0000
                Re: "Lete2??s Stop Bashing C" David Brown <david.brown@hesbynett.no> - 2016-12-08 19:58 +0100
                Re: "Lete2??s Stop Bashing C" supercat@casperkitty.com - 2016-12-08 08:22 -0800
                Re: "Lete2??s Stop Bashing C" David Brown <david.brown@hesbynett.no> - 2016-12-08 20:12 +0100
                Re: "Lete2??s Stop Bashing C" supercat@casperkitty.com - 2016-12-08 11:40 -0800
                Re: "Lete2??s Stop Bashing C" Robert Wessel <robertwessel2@yahoo.com> - 2016-12-10 02:44 -0600
                Re: "Lete2??s Stop Bashing C" Richard Heathfield <rjh@cpax.org.uk> - 2016-12-08 16:22 +0000
                Re: "Lete2??s Stop Bashing C" David Brown <david.brown@hesbynett.no> - 2016-12-08 20:14 +0100
                Re: "Lete2??s Stop Bashing C" Robert Wessel <robertwessel2@yahoo.com> - 2016-12-10 02:19 -0600
                Re: "Lete2??s Stop Bashing C" supercat@casperkitty.com - 2016-12-08 07:44 -0800
                Re: "Lete2??s Stop Bashing C" David Brown <david.brown@hesbynett.no> - 2016-12-08 22:05 +0100
                Re: "Lete2??s Stop Bashing C" jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-08 22:14 +0100
                Re: "Lete2??s Stop Bashing C" David Brown <david.brown@hesbynett.no> - 2016-12-09 10:39 +0100
                Re: "Lete2??s Stop Bashing C" supercat@casperkitty.com - 2016-12-08 13:33 -0800
                Re: "Lete2??s Stop Bashing C" David Brown <david.brown@hesbynett.no> - 2016-12-09 11:13 +0100
                Re: "Lete2??s Stop Bashing C" Robert Wessel <robertwessel2@yahoo.com> - 2016-12-07 06:27 -0600
                Re: "Lete2??s Stop Bashing C" supercat@casperkitty.com - 2016-12-07 07:17 -0800
                Re: "Lete2??s Stop Bashing C" Robert Wessel <robertwessel2@yahoo.com> - 2016-12-07 23:43 -0600
                Re: "Lete2??s Stop Bashing C" Ike Naar <ike@iceland.freeshell.org> - 2016-12-07 07:41 +0000
                Re: "Lete2??s Stop Bashing C" jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-07 11:45 +0100
                Re: "Lete2??s Stop Bashing C" Keith Thompson <kst-u@mib.org> - 2016-12-07 09:22 -0800
                Re: "Lete2??s Stop Bashing C" jacobnavia <jacob@jacob.remcomp.fr> - 2016-12-07 11:49 +0100
                Re: "Lete2??s Stop Bashing C" Jerry Stuckle <jstucklex@attglobal.net> - 2016-12-07 09:28 -0500
            Re: "Lete2��s Stop Bashing C" "James R. Kuyper" <jameskuyper@verizon.net> - 2016-12-06 14:22 -0500
            Re: Subject field encoding Noob <root@127.0.0.1> - 2016-12-07 21:40 +0100
              Re: Subject field encoding Keith Thompson <kst-u@mib.org> - 2016-12-07 13:01 -0800
              Re: Subject field encoding Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2016-12-07 16:02 -0500
            Re: "Lete2�™s Stop Bashing C" asetofsymbols@gmail.com - 2016-12-08 15:50 -0800
          Re: "Let’s Stop Bashing C" Richard Heathfield <rjh@cpax.org.uk> - 2016-12-06 19:07 +0000
    Re: "Let€™s Stop Bashing C" Xcott Craver <nospam@nospam.invalid> - 2016-12-07 16:48 -0500
      Re: "Let's Stop Bashing C" Noob <root@127.0.0.1> - 2016-12-07 23:29 +0100
  Re: "Let’s Stop Bashing C" "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2016-12-06 12:06 +0800

csiph-web