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Re: [Emacs-diffs] trunk r117464: Shrink Lisp_Sub_Char_Table by preferrin

From: Stefan Monnier
Subject: Re: [Emacs-diffs] trunk r117464: Shrink Lisp_Sub_Char_Table by preferring C integers to Lisp_Objects.
Date: Wed, 02 Jul 2014 11:42:02 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.4.50 (gnu/linux)

>> So, I think it's unsafe to cast your new "struct Lisp_Sub_Char_Table"
>> to a "struct Lisp_Vector".  Maybe it does work on current existing
>> systems, but it's too fragile.
> I'll install verify() to catch future (broken) systems.

The problem is not only future systems.  On systems where Lisp_Object
are 64bit but can be aligned on a 32bit boundary (I expect this to be
the case for some 32bit systems --with-wide-int), if/when we optimize
the representation a bit more (i.e. merge `depth' and `min_char' into
a single 32bit word, by adding ":2" and ":30" after each field), your
code will probably fail.


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