bug#8528: 24.0.50; 32-bit Emacs with apparent 128M buffer size limit

[Evans Winner]

My understanding is that a 32-bit GNU Emacs should be able
to open files up to 512 M.  If I am wrong about that, please
let me know.  I have compiled Emacs trunk from source
several times in the last couple of months and somewhere in
the last month or so it seems that the limit on my machine
has become 128 M.  My math could be off, but on the
assumption that 128 Mebibytes = 2^27 bytes = 1024 * 131072
bytes, and starting with emacs -Q I tried:

    $ dd if=/dev/zero of=testfile bs=1024 count=131072

and tried to open the file, and got: "Maximum buffer size
exceeded".  Then I tried one K less:

    $ dd if=/dev/zero of=testfile bs=1024 count=131071

and the buffer opened.

I have verified using the `top' command that there is
sufficient free memory for the files.

Also, for what it's worth:

    ELISP> most-positive-fixnum ==> 536870911

I discovered this as a result of not being able to open a
large (~160Mb) .pdf file that I had earlier been able to
open.  Please let me know if there is any other information
I can provide, or if there is something simple I am doing
wrong.


In GNU Emacs 24.0.50.1 (i686-pc-linux-gnu, GTK+ Version 3.0.8)
 of 2011-04-19 on braintron
Windowing system distributor `The X.Org Foundation', version 11.0.11001000
configured using `configure  '--with-x-toolkit=gtk3''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t