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From: Kim F. Storm
Subject: XGCTYPE, GC_NILP, GC_EQ, etc.
Date: Mon, 29 Nov 2004 10:17:55 +0100
User-agent: Gnus/5.11 (Gnus v5.11) Emacs/21.3.50 (gnu/linux)

To me, all the GC_ specific stuff in lisp.h seems to be superfluous
these days with the new mark bit implementations.

The trigger for GC_ stuff to be different seems to be these line in lisp.h:

/* During garbage collection, XGCTYPE must be used for extracting types
 so that the mark bit is ignored.  XMARKBIT accesses the markbit.
 Markbits are used only in particular slots of particular structure types.
 Other markbits are always zero.
 Outside of garbage collection, all mark bits are always zero.  */

#ifndef XGCTYPE
/* The distinction does not exist now that the MARKBIT has been eliminated.  */
#define XGCTYPE(a) XTYPE (a)

But XGCTYPE isn't defined anywhere else, so AFAICS, all the GC_SOMETHING is
always identical to SOMETHING.

So why keep this extra level of obsfuscation ?

Kim F. Storm <address@hidden> http://www.cua.dk

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