bug#8545: issues with recent doprnt-related changes

[Stefan Monnier <monnier@iro.umontreal.ca>]

>> >> It seems from that discussion that strings can contain
>> >> MOST_POSITIVE_FIXNUM bytes.
>> > I think the conclusion was that it can contain MOST_POSITIVE_FIXNUM
>> > _including_the_terminating_null_.
>> 
>> Hmm, that's not how I read
>> <http://lists.gnu.org/archive/html/emacs-devel/2011-04/msg00923.html>.
>> 
>> I understood the argument to be that a buffer must contain at most
>> MOST_POSITIVE_FIXNUM - 1 bytes due to other reasons, but it's OK
>> to have "a string whose length is MOST_POSITIVE_FIXNUM", i.e.,
>> (= (length STRING) most-positive-fixnum), because we already check
>> buffer sizes before inserting strings.  If you
>> count the trailing byte, the length of the underlying C character
>> array would be MOST_POSITIVE_FIXNUM + 1.

> Stefan, could you please chime in?

I'm not sure I understand the details more than you do.  AFAIK the
MOST_POSITIVE_FIXNUM limit only comes into play when the number goes
through Lisp_Object somewhere.  And we never show "length, including
terminating nul-byte" to Elisp, so the nul-byte shouldn't matter: while
the C array will have size MOST_POSITIVE_FIXNUM + 1, this will only be
represented in EMACS_INT which can accommodate it just fine.


        Stefan