Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
| From | jt@toerring.de (Jens Thoms Toerring) |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: micro-architectural details |
| Date | 2016-12-09 09:51 +0000 |
| Organization | Freie Universitaet Berlin |
| Message-ID | <eavd59F5kggU1@mid.uni-berlin.de> (permalink) |
| References | (8 earlier) <o27bm1$mgq$1@dont-email.me> <f80db400-a179-48ad-ac63-f6e954c08b8c@googlegroups.com> <o27g8v$arv$1@dont-email.me> <o29tdp$nbl$1@dont-email.me> <o2a39e$c8b$1@dont-email.me> |
jacobnavia <jacob@jacob.remcomp.fr> wrote:
> Le 07/12/2016 à 22:04, Noob a écrit :
> > On 07/12/2016 00:07, jacobnavia wrote:
> >
> >> Look, a non taken jump on overflow is one cycle. No memory access, since
> >> a CPU flag doesn't take any. The only overhead is code size:
> >
> > When you mention CPU-specific details, it's obvious you
> > have Intel CPUs in mind.
> Obvious of course. I am programming lcc-win for ARM-64, and have done
> versions for the power pc and even a 16 bit CPU.
> You do not know what you are talking about when you speak about me. You
> do not even know what I do.
> > Not all architectures have an
> > "overflow flag". Not all architectures have a "one cycle
> > penalty for non-taken jumps".
> >
> Yes, other architectures have more cycles. But programming is not about
> getting something in less cycles, it is about getting correct results!
Well, you're talking about a certain kind of programming. But
there are others too you don't seem to consider. Here's just
a data point.
I very recently had to modify the bootloader for an embedded
(ARM) system. This is the code that is loaded by the firmware
in the CPU from NAND (where it has to reside at a specific
address). Since at that time not even the controller for ex-
ternal SDRAM is initialized, the bootloader gets loaded into
CPU-internal RAM, of which there's only 4 kB. Thus the boot-
loader must be smaller than that, still leaving room for a
bit of stack. The bootloader does some hardware initiali-
zation (e.g. setting up the SDRAM controller and some other
crucial sub-systems) and then loads the kernel (and the device
tree blob) into (external) memory before passing control to
the now loaded kernel.
Obviously, correctness of that program is crucial. But it's
necessary that the program fits into those 4 kB of internal
CPU RAM. It was a very tight fit indeed, I ended up with
104 bytes left for the stack (that's space for just 26
addresses or integer data items).
The program doesn't do much integer arithmetic, but even a few
additional required instructions would have made it impossible
to squeeze it into the available space (or would have required
what amounts to a rewrite of the whole existing program, making
it incompatible to what's maintained up-stream and taking a real
lot of extra time).
Since nowadays C probably is mostly used in embedded pro-
gramming, where tight requirements are common, anything
like overflow checking or array bounds checking (something
else you seem to think should go into the language, if I
remember correctly) should definitely not be mandated by the
language. I find nothing to say against having that as optional
features (which some compilers, your's included, already sup-
port), it would be indeed nice in a number of circumstances -
I'd be the first to use them. But don't try to make that manda-
tory since it might render C unusable for an important field
of programming where it's now used everywhere.
Also speed can be an issue in this context. It's not uncommon
that you are dealing with a microcontroller that does not run
with a GHz clock but something in the single digit MHz range
and where there are severe time constraints on what can be
done e.g. in an interrupt handler and thus each cycle really
counts (yes, on those tiny things CPU time is still more or
less directly proportional to the number of instructions as
in the good old days of the Z-80 and friends;-)
Regards, Jens
--
\ Jens Thoms Toerring ___ jt@toerring.de
\__________________________ http://toerring.de
Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll 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