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Re: Is this really necessary

From Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups comp.lang.c++
Subject Re: Is this really necessary
Date 2021-08-11 12:40 -0700
Organization A noiseless patient Spider
Message-ID <86bl63zs5l.fsf@linuxsc.com> (permalink)
References (10 earlier) <serkdg$jh8$1@dont-email.me> <serkpm$36i$1@gioia.aioe.org> <ses4ec$si1$1@dont-email.me> <8635rh1m2i.fsf@linuxsc.com> <inffroF5l5hU1@mid.individual.net>

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Bo Persson <bo@bo-persson.se> writes:

> On 2021-08-10 at 15:11, Tim Rentsch wrote:
>
>> Vir Campestris <vir.campestris@invalid.invalid> writes:
>>
>> [..stuff about 64 bit systems removed..]
>>
>>> What bothers me about ptr_diff_t is the size.  The difference between
>>> two 32-bit pointers is plus or minus 4GB.  Which needs a 33 bit value
>>> :(
>>>
>>> As it happens it's never been a practical problem as I've never had a
>>> 32 bit system with more than 2GB RAM,
>>
>> It isn't necessary for there to be more than 2GB of RAM for
>> problems with ptrdiff_t to manifest (in 32-bit linux).  A call to
>> malloc() will gladly return a memory area larger than all of RAM
>> if there is swap space to hold it.
>
> There still has to be a contiguous address space that is free of
> already allocated memory blocks and not in a range reserved by the
> operating system.

True.

> I'm no Linux expert, but on Windows configured for LargeAddressAware
> programs, with 3 GB user + 1 GB OS, it is extremely unlikely to find a
> 2.x GB hole for the heap.

That depends on the program doesn't it?  And so is more unlikely
for some programs than others?

Of course it certainly is within the realm of possibility that on
Microsoft Windows the virtual address space is all chopped up
right from the get go.  The developers there are real geniuses,
who knows what they might have come up with.

> Or that you have a program that needs
> exactly 1 such block for byte sized operations.

Note that "byte sized operations" might be nothing more than
using character pointers to delimit region boundaries within
the memory area, and using pointer subtraction to determine
the size of various sub-areas.

Note also that there may be more than one such block provided
there is only one at a time.  In addition to malloc() there is
also free().  I ran a test case (on a 32-bit linux system) that
allocated five large memory regions, one at a time, each of which
was larger than 2 GB (and so larger than PTRDIFF_MAX in that
C implementation).

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Is this really necessary Bonita Montero <Bonita.Montero@gmail.com> - 2021-06-05 12:53 +0200
  Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-06-05 14:19 +0200
    Re: Is this really necessary Bonita Montero <Bonita.Montero@gmail.com> - 2021-06-05 14:27 +0200
      Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-06-05 14:33 +0200
        Re: Is this really necessary Bonita Montero <Bonita.Montero@gmail.com> - 2021-06-05 15:06 +0200
          Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-06-05 15:29 +0200
            Re: Is this really necessary Bonita Montero <Bonita.Montero@gmail.com> - 2021-06-05 17:38 +0200
              Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-06-05 17:51 +0200
              Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-06-05 11:56 -0400
            Re: Is this really necessary James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-06-05 19:08 -0400
              Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-06-06 11:24 +0200
              Re: Is this really necessary Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2021-06-06 10:33 +0100
                Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-06-06 07:56 -0400
                Re: Is this really necessary Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2021-06-06 15:00 +0100
                Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-06-06 16:20 -0700
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-06-07 00:44 -0700
                Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-06-07 12:13 -0700
                Re: Is this really necessary Bo Persson <bo@bo-persson.se> - 2021-06-07 21:58 +0200
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-07 10:25 -0700
                Re: Is this really necessary Bo Persson <bo@bo-persson.se> - 2021-08-07 21:21 +0200
          Re: Is this really necessary Öö Tiib <ootiib@hot.ee> - 2021-06-05 06:34 -0700
          Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-06-05 20:03 -0400
            Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-07 12:59 -0700
              Re: Is this really necessary MrSpud_85yGi2@1ahbfz.gov - 2021-08-08 09:18 +0000
                Re: Is this really necessary James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-08-08 09:23 -0400
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-08 15:04 +0000
                Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-08-08 13:14 -0400
                Re: Is this really necessary MrSpud_1dgrmf@dx58865qyrdw30lqllb.info - 2021-08-09 08:21 +0000
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-09 08:53 +0000
                Re: Is this really necessary "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-08-09 19:53 +0200
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-10 05:22 +0000
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-10 14:54 +0000
                Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-08-10 11:41 -0700
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-11 05:39 +0000
                Re: Is this really necessary Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2021-08-08 20:01 +0100
                Re: Is this really necessary MrSpud_ifhov@nldls6_1kg3nl2qnwv.biz - 2021-08-09 08:19 +0000
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-09 08:55 +0000
                Re: Is this really necessary James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-08-09 12:16 -0400
                Re: Is this really necessary MrSpud_HG@_0b772d8ha3yjo0xb.edu - 2021-08-09 16:23 +0000
                Re: Is this really necessary Vir Campestris <vir.campestris@invalid.invalid> - 2021-08-09 21:50 +0100
                Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-08-09 20:57 -0400
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-10 01:12 +0000
                Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-08-09 21:21 -0400
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-10 07:13 -0700
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-10 05:29 +0000
                Re: Is this really necessary MrSpud_12tus_Atff@bya886olr5o8dhu9.ac.uk - 2021-08-10 07:28 +0000
                Re: Is this really necessary Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2021-08-10 15:34 +0100
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-10 14:59 +0000
                Re: Is this really necessary MrSpud_wPgnov999o@vv7a6.tv - 2021-08-10 15:54 +0000
                Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-08-10 11:29 -0700
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-11 08:45 +0000
                Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-08-11 07:05 -0700
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-11 14:18 +0000
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-10 14:57 +0000
                Re: Is this really necessary MrSpud_pb9bpp7Ej@6urvt16b9fax.gov.uk - 2021-08-10 07:23 +0000
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-10 15:02 +0000
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-10 06:11 -0700
                Re: Is this really necessary Bo Persson <bo@bo-persson.se> - 2021-08-10 16:13 +0200
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-11 12:40 -0700
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-12 08:20 +0000
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-12 03:50 -0700
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-12 14:58 +0000
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-12 08:29 -0700
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-12 15:39 +0000
                Re: Is this really necessary Paavo Helde <myfirstname@osa.pri.ee> - 2021-08-12 20:07 +0300
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-13 07:16 +0000
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-13 09:26 +0000
                Re: Is this really necessary James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-08-13 10:30 -0400
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-13 14:58 +0000
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-14 08:07 +0000
                Re: Is this really necessary "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2021-08-14 10:40 -0700
                Re: Is this really necessary "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2021-08-14 10:38 -0700
                Re: Is this really necessary "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-08-13 15:30 +0200
                Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-08-13 11:18 -0700
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-14 03:20 -0700
                Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-08-14 13:24 -0700
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-14 20:33 +0000
                Re: Is this really necessary James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-08-15 00:40 -0400
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-15 07:02 -0700
                Re: Is this really necessary "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-08-15 21:19 +0200
                Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-08-15 15:42 -0400
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-21 12:38 -0700
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-14 08:13 +0000
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-14 02:58 -0700
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-13 14:32 +0000
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-14 02:28 -0700
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-14 03:00 -0700
                Re: Is this really necessary Bart <bc@freeuk.com> - 2021-08-14 14:03 +0100
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-14 15:06 +0000
                Re: Is this really necessary "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-08-12 12:06 -0700
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-13 09:19 +0000
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-13 14:35 +0000
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-13 14:58 +0000
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-10 15:03 +0000
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-11 12:54 -0700
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-11 20:20 +0000
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-12 03:42 -0700
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-11 05:45 +0000
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-11 05:26 -0700
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-11 14:06 +0000
                Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-08-11 14:01 +0000
                Re: Is this really necessary James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-08-09 23:20 -0400
                Re: Is this really necessary MrSpud_m7k7yilq_8@u6w.biz - 2021-08-10 07:26 +0000
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-10 07:51 +0000
                Re: Is this really necessary MrSpud_ggBp1lq0@lxz.tv - 2021-08-10 07:59 +0000
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-10 12:24 +0000
                Re: Is this really necessary MrSpud_u7lm@bxuc3wy1g3cxiqu5j2x1_7iu.com - 2021-08-10 15:51 +0000
                Re: Is this really necessary Juha Nieminen <nospam@thanks.invalid> - 2021-08-11 05:47 +0000
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-11 08:46 +0000
                Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-08-10 11:20 +0200
                Re: Is this really necessary James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-08-10 10:27 -0400
                Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-08-10 17:44 +0200
                Re: Is this really necessary MrSpud_885p_dugji@l6zhsgj_v6t3dbj.tv - 2021-08-10 15:50 +0000
                Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-08-11 08:31 +0200
                Re: Is this really necessary James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-08-10 10:27 -0400
                Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-08-10 11:27 -0700
                Re: Is this really necessary mickspud@downthefarm.com - 2021-08-11 08:44 +0000
                Re: Is this really necessary Paavo Helde <myfirstname@osa.pri.ee> - 2021-08-11 16:05 +0300
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-10 06:41 -0700
          Re: Is this really necessary Paavo Helde <myfirstname@osa.pri.ee> - 2021-06-06 18:48 +0300
            Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-06-06 14:26 -0400
            Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-06-06 16:10 -0700
              Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-06-06 21:30 -0400
                Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-06-06 18:49 -0700
                Re: Is this really necessary Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-06-06 18:51 -0700
                Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-06-06 22:57 -0400
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-06-07 09:43 -0700
                Re: Is this really necessary Öö Tiib <ootiib@hot.ee> - 2021-06-07 09:51 -0700
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-07 10:22 -0700
                Re: Is this really necessary "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2021-06-07 10:13 -0700
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-07 10:22 -0700
                Re: Is this really necessary "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2021-08-07 12:40 -0700
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-08-07 12:54 -0700
              Re: Is this really necessary Öö Tiib <ootiib@hot.ee> - 2021-06-06 23:17 -0700
            Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-06-07 09:19 -0700
              Re: Is this really necessary Paavo Helde <myfirstname@osa.pri.ee> - 2021-06-07 21:58 +0300
                Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-06-10 11:29 -0700
    Re: Is this really necessary Öö Tiib <ootiib@hot.ee> - 2021-06-05 05:38 -0700
      Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-06-05 15:41 +0200
        Re: Is this really necessary Öö Tiib <ootiib@hot.ee> - 2021-06-05 08:18 -0700
          Re: Is this really necessary Richard Damon <Richard@Damon-Family.org> - 2021-06-05 11:58 -0400
    Re: Is this really necessary MrSpook_rs7x@4hhtozmpj299zx.tv - 2021-06-05 16:00 +0000
      Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-06-05 18:16 +0200
        Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-06-06 17:34 +0200
        Re: Is this really necessary MrSpook_ie@q67rq6_2ly9ut44j.org - 2021-06-06 13:55 +0000
      Re: Is this really necessary Bo Persson <bo@bo-persson.se> - 2021-06-05 19:50 +0200
        Re: Is this really necessary MrSpook_zn7@4tzq7j92.gov - 2021-06-06 13:59 +0000
    Re: Is this really necessary James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-06-05 17:42 -0400
      Re: Is this really necessary David Brown <david.brown@hesbynett.no> - 2021-06-06 11:05 +0200
      Re: Is this really necessary Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-06-07 00:27 -0700
  Re: Is this really necessary Vir Campestris <vir.campestris@invalid.invalid> - 2021-06-06 21:27 +0100
    Re: Is this really necessary "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2021-06-07 00:22 +0200
      Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-06-07 14:53 +0000
        Re: Is this really necessary Bonita Montero <Bonita.Montero@gmail.com> - 2021-06-07 18:02 +0200
      Re: Is this really necessary Vir Campestris <vir.campestris@invalid.invalid> - 2021-06-16 21:38 +0100
    Re: Is this really necessary scott@slp53.sl.home (Scott Lurndal) - 2021-06-07 14:52 +0000

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