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Groups > comp.lang.c > #107609

Re: struct padding question

From Keith Thompson <kst-u@mib.org>
Newsgroups comp.lang.c
Subject Re: struct padding question
Date 2017-04-01 15:24 -0700
Organization None to speak of
Message-ID <lnfuhr3gx6.fsf@kst-u.example.com> (permalink)
References (1 earlier) <ob07qd$if0$1@dont-email.me> <obon1p$4aj$1@dont-email.me> <llsvdc55d0d8etsi9mlkfl6s7o01d16gr7@4ax.com> <lnk2742btb.fsf@kst-u.example.com> <5g70ectt3pqgkh64vqc2llk304v9aj4nj8@4ax.com>

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Robert Wessel <robertwessel2@yahoo.com> writes:
> On Sat, 01 Apr 2017 12:00:00 -0700, Keith Thompson <kst-u@mib.org>
> wrote:
>>Robert Wessel <robertwessel2@yahoo.com> writes:
>>[...]
>>> There have been implementations of, 10-byte (80-bit), x86 long double
>>> which have 2, 4, 8 and 16 byte alignment requirements.
>>>
>>> For example, amongst compilers actually supporting the 80-bit type, MS
>>> and Borland's 16-bit compilers use 2-byte alignment, several 32-bit
>>> (typical x86 GCC, for example) compilers use 4B alignment, Watcom uses
>>> 8B in both 16 and 32-bit versions, and most *nix compilers on 64B use
>>> 16B alignment, as does ICC on Windows in both 32 and 64B modes).  
>>>
>>> *Not* intended to be an exhaustive list.
>>
>>The size of a type must be a whole multiple of its alignment; arrays
>>cannot have gaps between elements.  If a 10-byte floating-point type
>>requires 4-byte alignment, it must be padded to at least 12 bytes.
>
> That's true, but MS/Borland long doubles on their 16-bit compilers had
> a size of 10 bytes (and 2B alignment).

Which is consistent with what I said.  But you also said that
a 10-byte long double could have a 4, 8, or 16 byte alignment,
which is not possible.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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Thread

struct padding question MehdiAmini <atorrses@gmail.com> - 2017-03-23 14:28 +0430
  Re: struct padding question David Brown <david.brown@hesbynett.no> - 2017-03-23 11:28 +0100
    Re: struct padding question MehdiAmini <atorrses@gmail.com> - 2017-03-23 16:44 +0430
      Re: struct padding question jm.bourguet@gmail.com - 2017-03-23 05:30 -0700
      Re: struct padding question Keith Thompson <kst-u@mib.org> - 2017-03-23 08:45 -0700
    Re: struct padding question Noob <root@127.0.0.1> - 2017-04-01 19:15 +0200
      Re: struct padding question tim prince <n8tm@aol.com> - 2017-04-01 14:41 -0400
        Re: struct padding question supercat@casperkitty.com - 2017-04-02 09:15 -0700
          Re: struct padding question scott@slp53.sl.home (Scott Lurndal) - 2017-04-03 13:51 +0000
            Re: struct padding question supercat@casperkitty.com - 2017-04-03 07:48 -0700
              Re: struct padding question scott@slp53.sl.home (Scott Lurndal) - 2017-04-03 15:47 +0000
                Re: struct padding question supercat@casperkitty.com - 2017-04-03 09:24 -0700
      Re: struct padding question Keith Thompson <kst-u@mib.org> - 2017-04-01 11:43 -0700
      Re: struct padding question Robert Wessel <robertwessel2@yahoo.com> - 2017-04-01 13:46 -0500
        Re: struct padding question Keith Thompson <kst-u@mib.org> - 2017-04-01 12:00 -0700
          Re: struct padding question Robert Wessel <robertwessel2@yahoo.com> - 2017-04-01 16:40 -0500
            Re: struct padding question Keith Thompson <kst-u@mib.org> - 2017-04-01 15:24 -0700
              Re: struct padding question Robert Wessel <robertwessel2@yahoo.com> - 2017-04-03 17:46 -0500
  Re: struct padding question BartC <bc@freeuk.com> - 2017-03-23 11:50 +0000
    Re: struct padding question David Brown <david.brown@hesbynett.no> - 2017-03-23 14:08 +0100
      Re: struct padding question BartC <bc@freeuk.com> - 2017-03-23 13:31 +0000
        Re: struct padding question David Brown <david.brown@hesbynett.no> - 2017-03-23 14:46 +0100
          Re: struct padding question BartC <bc@freeuk.com> - 2017-03-23 14:07 +0000
            Re: struct padding question David Brown <david.brown@hesbynett.no> - 2017-03-23 15:52 +0100
              Re: struct padding question scott@slp53.sl.home (Scott Lurndal) - 2017-03-23 17:19 +0000
                Re: struct padding question David Brown <david.brown@hesbynett.no> - 2017-03-23 19:57 +0100
      Re: struct padding question Ian Pilcher <arequipeno@gmail.com> - 2017-03-23 08:52 -0500
        Re: struct padding question David Brown <david.brown@hesbynett.no> - 2017-03-23 15:54 +0100
          Re: struct padding question supercat@casperkitty.com - 2017-03-23 08:29 -0700
  Re: struct padding question GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-03-23 14:04 +0100
    Re: struct padding question MehdiAmini <atorrses@gmail.com> - 2017-03-23 20:32 +0430
      Re: struct padding question GOTHIER Nathan <nathan.gothier@gmail.com> - 2017-03-23 18:35 +0100
      Re: struct padding question supercat@casperkitty.com - 2017-03-23 12:02 -0700
        Re: struct padding question Keith Thompson <kst-u@mib.org> - 2017-03-23 12:21 -0700
          Re: struct padding question supercat@casperkitty.com - 2017-03-23 12:55 -0700
  Re: struct padding question Les Cargill <lcargill99@comcast.com> - 2017-03-25 15:12 -0500

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