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Re: struct padding question

From GOTHIER Nathan <nathan.gothier@gmail.com>
Newsgroups comp.lang.c
Subject Re: struct padding question
Date 2017-03-23 18:35 +0100
Organization A noiseless patient Spider
Message-ID <20170323183521.27ca5598f993dd7a3b3d67cc@gmail.com> (permalink)
References <ob062g$coi$1@dont-email.me> <20170323140413.9a2515568baa60870b1b6570@gmail.com> <ob0rcp$s7g$1@dont-email.me>

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On Thu, 23 Mar 2017 20:32:15 +0430
MehdiAmini <atorrses@gmail.com> wrote:

> On 03/23/2017 05:34 PM, GOTHIER Nathan wrote:
> > On Thu, 23 Mar 2017 14:28:23 +0430
> > MehdiAmini <atorrses@gmail.com> wrote:
> 
> [...]
> 
> > You should better use 64-bit aligned floats such as float or double rather than
> > the 80-bit aligned long double assuming your processor is AMD64 compatible. I
> > would recommend to use the long double type only for intermediate calculation
> > and not for aggregates such as arrays or structures.
> >
> 
> using:
> printf("%zu %zu\n",sizeof (long double),alignof(long double));
> 
> I get:
> 16 16
> 
> Not 80-bit.

https://en.wikipedia.org/wiki/Long_double

Indeed. The alignment depends on the implementation but anyway if your FPU
doesn't support more than 80-bits floats, you're wasting some memory space to
store the result in 128 bits to benefit of a correctly rounded 64-bit double.

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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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