[Octave-bug-tracker] [bug #51638] mach-info.cc uses unguaranteed behavior to determine endian-ness

[Rik]

URL:
  <http://savannah.gnu.org/bugs/?51638>

                 Summary: mach-info.cc uses unguaranteed behavior to determine
endian-ness
                 Project: GNU Octave
            Submitted by: rik5
            Submitted on: Tue 01 Aug 2017 11:21:02 AM PDT
                Category: Configuration and Build System
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Other
                  Status: Confirmed
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: Any

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Details:

The file liboctave/system/mach-info.cc writes a value into one union member,
and then reads from a second union member.  This behavior is
implementation-dependent in C++ (see
http://en.cppreference.com/w/cpp/language/union).

Either mach-info.cc needs to be re-coded to avoid this construct, or the file
should be downgraded to a straight C language file where the code usage in
question is guaranteed.

For a much longer article on determining endian-ness in C++, see
http://dbp-consulting.com/tutorials/StrictAliasing.html




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