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To: Andrew Haley <aph@redhat.com>
Cc: Jason Merrill <jason@redhat.com>,
        Gabriel Dos Reis <gdr@integrable-solutions.net>,
        Jamie Lokier <jamie@shareable.org>, gcc@gcc.gnu.org
Subject: Re: On alignment
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From: Tom Tromey <tromey@redhat.com>
Reply-To: tromey@redhat.com
X-Attribution:  Tom
X-Zippy:  HAIR TONICS, please!!
Date: Thu, 01 May 2003 23:50:00 -0000
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>>>>> "Andrew" == Andrew Haley <aph@redhat.com> writes:

Jason> A similar trick using offsetof should work with all versions of
Jason> gcc; just add a char field to the beginning of the struct, and
Jason> measure the offset to the TYPE field.

Andrew> Ah, okay.  That sounds pretty neat.

Andrew> Tom, time for the third (or is it fourth) version of your patch.  :-)

How will this work?  We can't do this:

    template<typename T>
    struct aligner
    {
      char dummy;
      T field;
    }

A plain offsetof(aligner<jbyte>, field) will yield the wrong answer (2
instead of 1).  I guess one answer would be "don't bother with byte or
boolean".


What will eventually go wrong with what we have now?

    template<typename T>
    struct aligner
    {
      T field;
    };

    #define ALIGNOF(TYPE) (__alignof__ (((aligner<TYPE> *) 0)->field))

Tom