Re: Computer architects leaving Intel...

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Sujet : Re: Computer architects leaving Intel...
De : tr.17687 (at) *nospam* z991.linuxsc.com (Tim Rentsch)
Groupes : comp.arch
Date : 10. Sep 2024, 15:37:59
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Organisation : A noiseless patient Spider
Message-ID : <861q1ring8.fsf@linuxsc.com>
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Michael S <already5chosen@yahoo.com> writes:

On Sun, 08 Sep 2024 15:36:39 GMT
anton@mips.complang.tuwien.ac.at (Anton Ertl) wrote:
>
Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
>
anton@mips.complang.tuwien.ac.at (Anton Ertl) writes:
>
There was still no easy way to determine whether your software
that calls memcpy() actually works as expected on all hardware,
>
There may not be a way to tell if memcpy()-calling code will work
on platforms one doesn't have, but there is a relatively simple
and portable way to tell if some memcpy() call crosses over into
the realm of undefined behavior.
>
1) At first I thought that yes, one could just check whether there is
an overlap of the memory areas.  But then I remembered that you cannot
write such a check in standard C without (in the general case)
exercising undefined behaviour;  and then the compiler could eliminate
the check or do something else that's unexpected.  Do you have such a
check in mind that does not exercise undefined behaviour in the
general case?
>
The check that reliably catches all overlaps seems easy.
E.g. (src <= dst) == (src+len > dst)
>
In theory, on unusual hardware platform it can give false positives.
May be, for task in hand that's o.k.

The challenge is to find portable C that doesn't enter the arena
of undefined behavior (and also detects exactly those cases where
overlap occurs), and that is quite a stringent criterion.

The comparison shown works if src and dst both point to elements
of the same array.  But if they don't, comparing pointers to see
if one is less than another (or any of <, <=, >, >=) is undefined
behavior.  At the bit level it wouldn't surprise me to learn that
the test shown always returns accurate information.  However the
C standard doesn't promise that a bit-level comparison will be
done, and implementations are allowed to do anything at all for
this test in cases where src and dst point to (somewhere within)
different top-level objects.  What the hardware does doesn't
matter - what needs to be satisfied are the rules of the C
standard, and they are less forgiving.

I should add that I appreciate your proposed solution;  it's
better than what I think I would have come up with under a
similar set of assumptions.

Date Sujet#  Auteur
27 Aug 24 * Computer architects leaving Intel...539Thomas Koenig
27 Aug 24 +- Re: Computer architects leaving Intel...1Michael S
27 Aug 24 +- Re: Computer architects leaving Intel...1Stephen Fuld
27 Aug 24 `* Re: Computer architects leaving Intel...536John Dallman
28 Aug 24  +* Re: Computer architects leaving Intel...529BGB
28 Aug 24  i`* Re: Computer architects leaving Intel...528MitchAlsup1
28 Aug 24  i `* Re: Computer architects leaving Intel...527BGB
28 Aug 24  i  +* Re: Computer architects leaving Intel...2Robert Finch
28 Aug 24  i  i`- Re: Computer architects leaving Intel...1BGB
28 Aug 24  i  `* Re: Computer architects leaving Intel...524MitchAlsup1
29 Aug 24  i   `* Re: Computer architects leaving Intel...523BGB
29 Aug 24  i    +* Re: Computer architects leaving Intel...511MitchAlsup1
29 Aug 24  i    i`* Re: Computer architects leaving Intel...510BGB
30 Aug 24  i    i +* Re: Computer architects leaving Intel...499John Dallman
30 Aug 24  i    i i+* Re: Computer architects leaving Intel...11Thomas Koenig
30 Aug 24  i    i ii+- Re: Computer architects leaving Intel...1Michael S
30 Aug 24  i    i ii+* Re: Computer architects leaving Intel...8Anton Ertl
30 Aug 24  i    i iii+* Re: Computer architects leaving Intel...2Michael S
30 Aug 24  i    i iiii`- Re: Computer architects leaving Intel...1Anton Ertl
30 Aug 24  i    i iii`* Re: Computer architects leaving Intel...5John Dallman
30 Aug 24  i    i iii `* Re: Computer architects leaving Intel...4Brett
30 Aug 24  i    i iii  +- Re: Computer architects leaving Intel...1John Dallman
2 Sep 24  i    i iii  `* Re: Computer architects leaving Intel...2Terje Mathisen
2 Sep 24  i    i iii   `- Re: Computer architects leaving Intel...1Thomas Koenig
30 Aug 24  i    i ii`- Re: Computer architects leaving Intel...1BGB
30 Aug 24  i    i i`* Re: Computer architects leaving Intel...487Anton Ertl
30 Aug 24  i    i i +* Re: Computer architects leaving Intel...302John Dallman
30 Aug 24  i    i i i`* Re: Computer architects leaving Intel...301David Brown
30 Aug 24  i    i i i +* Re: Computer architects leaving Intel...293Anton Ertl
30 Aug 24  i    i i i i`* Re: Computer architects leaving Intel...292Bernd Linsel
31 Aug 24  i    i i i i +- Re: Computer architects leaving Intel...1Thomas Koenig
31 Aug 24  i    i i i i `* Re: Computer architects leaving Intel...290Thomas Koenig
31 Aug 24  i    i i i i  +- Re: Computer architects leaving Intel...1Thomas Koenig
31 Aug 24  i    i i i i  `* Re: Computer architects leaving Intel...288Bernd Linsel
31 Aug 24  i    i i i i   +- Re: Computer architects leaving Intel...1Thomas Koenig
31 Aug 24  i    i i i i   +* Re: Computer architects leaving Intel...2Thomas Koenig
31 Aug 24  i    i i i i   i`- Re: Computer architects leaving Intel...1Bernd Linsel
31 Aug 24  i    i i i i   `* Re: Computer architects leaving Intel...284Anton Ertl
31 Aug 24  i    i i i i    +* Re: Computer architects leaving Intel...279Thomas Koenig
31 Aug 24  i    i i i i    i+* Re: Computer architects leaving Intel...157Bernd Linsel
31 Aug 24  i    i i i i    ii+* Re: Computer architects leaving Intel...153MitchAlsup1
1 Sep 24  i    i i i i    iii`* Re: Computer architects leaving Intel...152Stephen Fuld
2 Sep 24  i    i i i i    iii `* Re: Computer architects leaving Intel...151Terje Mathisen
2 Sep 24  i    i i i i    iii  `* Re: Computer architects leaving Intel...150Stephen Fuld
3 Sep 24  i    i i i i    iii   +* Re: Computer architects leaving Intel...139David Brown
3 Sep 24  i    i i i i    iii   i+* Re: Computer architects leaving Intel...108Stephen Fuld
4 Sep 24  i    i i i i    iii   ii`* Re: Computer architects leaving Intel...107David Brown
4 Sep 24  i    i i i i    iii   ii +* Re: Computer architects leaving Intel...103Terje Mathisen
4 Sep 24  i    i i i i    iii   ii i+* Re: Computer architects leaving Intel...101David Brown
4 Sep 24  i    i i i i    iii   ii ii+* Re: Computer architects leaving Intel...97jseigh
4 Sep 24  i    i i i i    iii   ii iii`* Re: Computer architects leaving Intel...96David Brown
4 Sep 24  i    i i i i    iii   ii iii `* Re: Computer architects leaving Intel...95Brett
4 Sep 24  i    i i i i    iii   ii iii  +- Re: Computer architects leaving Intel...1Thomas Koenig
4 Sep 24  i    i i i i    iii   ii iii  +- Re: Computer architects leaving Intel...1MitchAlsup1
5 Sep 24  i    i i i i    iii   ii iii  +* Re: Computer architects leaving Intel...8BGB
5 Sep 24  i    i i i i    iii   ii iii  i`* Re: Computer architects leaving Intel...7MitchAlsup1
5 Sep 24  i    i i i i    iii   ii iii  i `* Re: Computer architects leaving Intel...6David Brown
5 Sep 24  i    i i i i    iii   ii iii  i  `* Re: Computer architects leaving Intel...5Niklas Holsti
5 Sep 24  i    i i i i    iii   ii iii  i   `* Re: Computer architects leaving Intel...4David Brown
6 Sep 24  i    i i i i    iii   ii iii  i    `* Re: Computer architects leaving Intel...3BGB
6 Sep 24  i    i i i i    iii   ii iii  i     `* Re: Computer architects leaving Intel...2David Brown
9 Sep 24  i    i i i i    iii   ii iii  i      `- Re: Computer architects leaving Intel...1BGB
5 Sep 24  i    i i i i    iii   ii iii  +* Re: Computer architects leaving Intel...83David Brown
5 Sep 24  i    i i i i    iii   ii iii  i`* Re: Computer architects leaving Intel...82Terje Mathisen
5 Sep 24  i    i i i i    iii   ii iii  i +* Re: Computer architects leaving Intel...79David Brown
5 Sep 24  i    i i i i    iii   ii iii  i i+* Re: Computer architects leaving Intel...2Thomas Koenig
7 Sep 24  i    i i i i    iii   ii iii  i ii`- Re: Computer architects leaving Intel...1Tim Rentsch
5 Sep 24  i    i i i i    iii   ii iii  i i+* Re: Computer architects leaving Intel...74Terje Mathisen
5 Sep 24  i    i i i i    iii   ii iii  i ii+* Re: Computer architects leaving Intel...16David Brown
9 Sep 24  i    i i i i    iii   ii iii  i iii`* Re: Computer architects leaving Intel...15Terje Mathisen
9 Sep 24  i    i i i i    iii   ii iii  i iii +* Re: Computer architects leaving Intel...12David Brown
9 Sep 24  i    i i i i    iii   ii iii  i iii i`* Re: Computer architects leaving Intel...11Brett
10 Sep 24  i    i i i i    iii   ii iii  i iii i +* Re: Computer architects leaving Intel...5Terje Mathisen
10 Sep 24  i    i i i i    iii   ii iii  i iii i i`* Re: Computer architects leaving Intel...4Brett
10 Sep 24  i    i i i i    iii   ii iii  i iii i i +* Re: Computer architects leaving Intel...2Michael S
11 Sep 24  i    i i i i    iii   ii iii  i iii i i i`- Re: Computer architects leaving Intel...1Brett
11 Sep 24  i    i i i i    iii   ii iii  i iii i i `- Re: Computer architects leaving Intel...1Terje Mathisen
10 Sep 24  i    i i i i    iii   ii iii  i iii i `* Re: Computer architects leaving Intel...5David Brown
10 Sep 24  i    i i i i    iii   ii iii  i iii i  +* Re: Computer architects leaving Intel...3Anton Ertl
10 Sep 24  i    i i i i    iii   ii iii  i iii i  i`* Re: Computer architects leaving Intel...2David Brown
10 Sep 24  i    i i i i    iii   ii iii  i iii i  i `- Re: Computer architects leaving Intel...1Stefan Monnier
10 Sep 24  i    i i i i    iii   ii iii  i iii i  `- Re: Computer architects leaving Intel...1BGB
9 Sep 24  i    i i i i    iii   ii iii  i iii `* Re: Computer architects leaving Intel...2Michael S
10 Sep 24  i    i i i i    iii   ii iii  i iii  `- Re: Computer architects leaving Intel...1Michael S
5 Sep 24  i    i i i i    iii   ii iii  i ii+* Re: Computer architects leaving Intel...45Bernd Linsel
6 Sep 24  i    i i i i    iii   ii iii  i iii+- Re: Computer architects leaving Intel...1David Brown
9 Sep 24  i    i i i i    iii   ii iii  i iii+* Re: Computer architects leaving Intel...2Terje Mathisen
9 Sep 24  i    i i i i    iii   ii iii  i iiii`- Re: Computer architects leaving Intel...1Tim Rentsch
14 Sep 24  i    i i i i    iii   ii iii  i iii`* Re: Computer architects leaving Intel...41Kent Dickey
14 Sep 24  i    i i i i    iii   ii iii  i iii +* Re: Computer architects leaving Intel...32Anton Ertl
14 Sep 24  i    i i i i    iii   ii iii  i iii i+* Re: Computer architects leaving Intel...29MitchAlsup1
14 Sep 24  i    i i i i    iii   ii iii  i iii ii`* Re: Computer architects leaving Intel...28Thomas Koenig
15 Sep 24  i    i i i i    iii   ii iii  i iii ii `* Re: Computer architects leaving Intel...27David Brown
16 Sep 24  i    i i i i    iii   ii iii  i iii ii  +* Re: Computer architects leaving Intel...5Thomas Koenig
16 Sep 24  i    i i i i    iii   ii iii  i iii ii  i`* Re: Computer architects leaving Intel...4David Brown
16 Sep 24  i    i i i i    iii   ii iii  i iii ii  i `* Re: Computer architects leaving Intel...3Thomas Koenig
17 Sep 24  i    i i i i    iii   ii iii  i iii ii  i  +- Re: Upwards and downwards compatible, Computer architects leaving Intel...1John Levine
17 Sep 24  i    i i i i    iii   ii iii  i iii ii  i  `- Re: Computer architects leaving Intel...1David Brown
16 Sep 24  i    i i i i    iii   ii iii  i iii ii  `* Re: Computer architects leaving Intel...21Terje Mathisen
16 Sep 24  i    i i i i    iii   ii iii  i iii ii   `* Re: Computer architects leaving Intel...20David Brown
16 Sep 24  i    i i i i    iii   ii iii  i iii ii    +* Re: Computer architects leaving Intel...14Michael S
17 Sep 24  i    i i i i    iii   ii iii  i iii ii    `* Re: Computer architects leaving Intel...5Terje Mathisen
15 Sep 24  i    i i i i    iii   ii iii  i iii i`* Re: Computer architects leaving Intel...2BGB
14 Sep 24  i    i i i i    iii   ii iii  i iii +* Re: Computer architects leaving Intel...3Thomas Koenig
16 Sep 24  i    i i i i    iii   ii iii  i iii `* Re: Computer architects leaving Intel...5Tim Rentsch
6 Sep 24  i    i i i i    iii   ii iii  i ii+* Re: Computer architects leaving Intel...3Tim Rentsch
7 Sep 24  i    i i i i    iii   ii iii  i ii`* Re: Computer architects leaving Intel...9Chris M. Thomasson
5 Sep 24  i    i i i i    iii   ii iii  i i`* Re: Computer architects leaving Intel...2MitchAlsup1
5 Sep 24  i    i i i i    iii   ii iii  i `* Re: Computer architects leaving Intel...2MitchAlsup1
7 Sep 24  i    i i i i    iii   ii iii  `- Re: Computer architects leaving Intel...1Tim Rentsch
4 Sep 24  i    i i i i    iii   ii ii`* Re: Computer architects leaving Intel...3Thomas Koenig
6 Sep 24  i    i i i i    iii   ii i`- Re: Computer architects leaving Intel...1Chris M. Thomasson
4 Sep 24  i    i i i i    iii   ii +- Re: Computer architects leaving Intel...1jseigh
13 Sep 24  i    i i i i    iii   ii `* Re: Computer architects leaving Intel...2Stephen Fuld
3 Sep 24  i    i i i i    iii   i`* Re: Computer architects leaving Intel...30Stefan Monnier
3 Sep 24  i    i i i i    iii   `* Re: Computer architects leaving Intel...10Terje Mathisen
31 Aug 24  i    i i i i    ii`* Re: Computer architects leaving Intel...3Thomas Koenig
1 Sep 24  i    i i i i    i`* Re: Computer architects leaving Intel...121David Brown
1 Sep 24  i    i i i i    +* Re: Computer architects leaving Intel...3John Dallman
3 Sep 24  i    i i i i    `- Re: Computer architects leaving Intel...1Stefan Monnier
30 Aug 24  i    i i i +- Re: Computer architects leaving Intel...1MitchAlsup1
30 Aug 24  i    i i i +* Re: Computer architects leaving Intel...4Stefan Monnier
30 Aug 24  i    i i i `* Re: Computer architects leaving Intel...2John Dallman
8 Sep 24  i    i i `* Re: Computer architects leaving Intel...184Tim Rentsch
30 Aug 24  i    i `* Re: Computer architects leaving Intel...10MitchAlsup1
31 Aug 24  i    `* Re: Computer architects leaving Intel...11Paul A. Clayton
29 Aug 24  `* Re: Computer architects leaving Intel...6Anton Ertl

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