Re: in place swap of float types

From	Robert Wessel <robertwessel2@yahoo.com>
Newsgroups	comp.lang.c
Subject	Re: in place swap of float types
Message-ID	<9ddbme52b398c5lrr1c653lvdo2oe7qbv5@4ax.com> (permalink)
References	<slrnqmaoja.4b2.3queens@cpe-65-25-200-198.new.res.rr.com>
Organization	Forte - www.forteinc.com
Date	2019-08-27 17:59 -0500

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On Tue, 27 Aug 2019 17:03:38 -0000 (UTC), 3queens@shabbyroad.com
wrote:

>Some time ago, there was a thread concerning using "a^=b; b^=a; a^=b" 
>to do an in place swap of two variables of the same size.  It was
>pointed out that this can only be done with integer types.  I found a
>way to do it with floating point types as well.
>
>Declare a union with the floating point variable and an equally long
>integer variable.  Then use the integer member to do the exclusive-or
>process.
>
>Naturally, this would not be efficient if the data had to be copied into
>and out of the union, but if the variables were defined as unions to
>begin with, this would work.
>
>Maybe not that useful, but if space is really tight, perhaps useful in
>some situations.


AFAIK, this invokes undefined behavior.  You cannot reliably read from
a different member of a union than was written to.

Thread

in place swap of float types 3queens@shabbyroad.com - 2019-08-27 17:03 +0000
  Re: in place swap of float types Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-08-27 19:22 +0000
    Re: in place swap of float types Andrew Smallshaw <andrews@sdf.org> - 2019-09-02 15:25 +0000
      Re: in place swap of float types Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-09-02 19:37 +0000
        Re: in place swap of float types Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-09-03 06:37 -0700
          Re: in place swap of float types David Brown <david.brown@hesbynett.no> - 2019-09-03 16:13 +0200
            Re: in place swap of float types Bart <bc@freeuk.com> - 2019-09-03 16:54 +0100
              Re: in place swap of float types David Brown <david.brown@hesbynett.no> - 2019-09-04 11:19 +0200
                Re: in place swap of float types Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-09-04 02:35 -0700
                Re: in place swap of float types David Brown <david.brown@hesbynett.no> - 2019-09-04 12:31 +0200
                Re: in place swap of float types Bart <bc@freeuk.com> - 2019-09-04 12:12 +0100
                Re: in place swap of float types David Brown <david.brown@hesbynett.no> - 2019-09-04 15:53 +0200
                Re: in place swap of float types Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-09-04 07:17 -0700
                Re: in place swap of float types David Brown <david.brown@hesbynett.no> - 2019-09-05 15:12 +0200
                Re: in place swap of float types Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-09-05 21:11 +0100
                Re: in place swap of float types Bart <bc@freeuk.com> - 2019-09-04 16:30 +0100
                Re: in place swap of float types jadill33@gmail.com - 2019-09-04 10:26 -0700
                Re: in place swap of float types Ike Naar <ike@iceland.freeshell.org> - 2019-09-05 06:00 +0000
                Re: in place swap of float types Bart <bc@freeuk.com> - 2019-09-05 11:14 +0100
                Re: in place swap of float types David Brown <david.brown@hesbynett.no> - 2019-09-05 14:54 +0200
                Re: in place swap of float types Bart <bc@freeuk.com> - 2019-09-05 15:48 +0100
                Re: in place swap of float types David Brown <david.brown@hesbynett.no> - 2019-09-06 10:35 +0200
                Re: in place swap of float types Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-09-06 02:52 -0700
                Re: in place swap of float types David Brown <david.brown@hesbynett.no> - 2019-09-06 13:18 +0200
                Re: in place swap of float types Bart <bc@freeuk.com> - 2019-09-06 12:14 +0100
                Re: in place swap of float types David Brown <david.brown@hesbynett.no> - 2019-09-06 15:08 +0200
                Re: in place swap of float types Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-09-06 06:23 -0700
                Re: in place swap of float types Keith Thompson <kst-u@mib.org> - 2019-09-04 14:16 -0700
                Re: in place swap of float types Bart <bc@freeuk.com> - 2019-09-04 22:42 +0100
                Re: in place swap of float types Keith Thompson <kst-u@mib.org> - 2019-09-04 15:21 -0700
                Re: in place swap of float types David Brown <david.brown@hesbynett.no> - 2019-09-05 15:15 +0200
              Re: in place swap of float types Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2019-09-04 08:05 -0600
                Re: in place swap of float types David Brown <david.brown@hesbynett.no> - 2019-09-05 15:17 +0200
                Re: in place swap of float types Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2019-09-05 20:28 -0600
                Re: in place swap of float types David Brown <david.brown@hesbynett.no> - 2019-09-06 10:39 +0200
                Re: in place swap of float types Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2019-09-06 08:11 -0600
                Re: in place swap of float types scott@slp53.sl.home (Scott Lurndal) - 2019-09-06 18:31 +0000
          Re: in place swap of float types Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-09-04 19:02 +0000
      Re: in place swap of float types David Brown <david.brown@hesbynett.no> - 2019-09-02 22:16 +0200
  Re: in place swap of float types Robert Wessel <robertwessel2@yahoo.com> - 2019-08-27 17:59 -0500
    Re: in place swap of float types Richard Damon <Richard@Damon-Family.org> - 2019-08-27 17:45 -0700
    Re: in place swap of float types James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-08-27 20:48 -0400
      Re: in place swap of float types Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-09-03 06:17 -0700
    Re: in place swap of float types Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-08-28 02:09 +0100
    Re: in place swap of float types Siri Cruise <chine.bleu@yahoo.com> - 2019-08-27 21:26 -0700
    Re: in place swap of float types David Brown <david.brown@hesbynett.no> - 2019-08-28 09:22 +0200
    Re: in place swap of float types Andrey Tarasevich <andreytarasevich@hotmail.com> - 2019-08-28 16:36 -0700
  Re: in place swap of float types David Brown <david.brown@hesbynett.no> - 2019-08-28 09:36 +0200
    Re: in place swap of float types Bart <bc@freeuk.com> - 2019-08-28 12:02 +0100
      Re: in place swap of float types James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-08-28 05:08 -0700
        Re: in place swap of float types Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-08-28 05:26 -0700
        Re: in place swap of float types David Brown <david.brown@hesbynett.no> - 2019-08-28 14:40 +0200
        Re: in place swap of float types Keith Thompson <kst-u@mib.org> - 2019-08-28 13:01 -0700
    Re: in place swap of float types Philipp Klaus Krause <pkk@spth.de> - 2019-09-04 11:18 +0200
      Re: in place swap of float types David Brown <david.brown@hesbynett.no> - 2019-09-04 12:57 +0200
        Re: in place swap of float types Philipp Klaus Krause <pkk@spth.de> - 2019-09-04 13:24 +0200
  Re: in place swap of float types Bonita Montero <Bonita.Montero@gmail.com> - 2019-09-05 08:18 +0200
    Re: in place swap of float types David Brown <david.brown@hesbynett.no> - 2019-09-05 15:19 +0200
      Re: in place swap of float types Bonita Montero <Bonita.Montero@gmail.com> - 2019-09-05 16:18 +0200
        Re: in place swap of float types Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-09-05 07:32 -0700
          Re: in place swap of float types Bonita Montero <Bonita.Montero@gmail.com> - 2019-09-05 17:32 +0200
          Re: in place swap of float types David Brown <david.brown@hesbynett.no> - 2019-09-06 10:54 +0200
            Re: in place swap of float types Bonita Montero <Bonita.Montero@gmail.com> - 2019-09-06 14:23 +0200

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