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Re: max buffer size problem


From: Eli Zaretskii
Subject: Re: max buffer size problem
Date: Wed, 8 Nov 2000 09:06:21 +0200 (IST)

On Tue, 7 Nov 2000 address@hidden wrote:

> I work on a system with huge amounts of resources (24 cpu's with 2GB
> RAM per cpu).  It is a real defect for the maximum buffer size to be
> less than a GB.  I ought to have a convenient means (e.g., a
> variable) to increase the default.

You can't do that.  The maximum buffer size is not an arbitrary limit
(arbitrary limits are against GNU coding standards); it is determined
by the representation of a Lisp integer used by Emacs Lisp.

An Emacs Lisp integer uses only 28 bits, because the other 4 bits of a
32-bit int are required for tagging Lisp data types.  This
implementation was chosen so that manipulating integer numbers will be
as fast in Lisp as it is in C (as opposed to other Lisp data types,
which require indirection through a pointer stored in those 28 bits).

The only way to break out of this limit without sacrificing
performance is to compile Emacs with a compiler whose `int' is 64-bit
wide.  The next release of Emacs will support this on several popular
systems which have such compilers.



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