Re: B-Tree support function number 3 (strxfrm() optimization)

On Sun, Jul 27, 2014 at 8:23 AM, Greg Stark <stark(at)mit(dot)edu> wrote:
> I haven't looked yet. Can you describe what exactly the AC_TRY_RUN is
> testing for?

It's more or less testing for a primary weight level (i.e. the first
part of the blob) that is no larger than the original characters of
the string, and has no "header bytes" or other redundancies. It also
matches secondary and subsequently weight levels to ensure that they
match, since the two stings tested have identical case, use of
diacritics, etc (they're both lowercase ASCII-safe strings). I don't
set a locale, but that shouldn't matter. I have good reason to believe
that many strxfrm() implementations behave this way, based on the
Unicode standard, and some investigation. Still, that is something
that can be more formally verified as long as we're not trusting of
strxfrm() generally rather than just discriminating against Mac OS X
specifically. I think that the Mac OS X implementation is an anomaly
(I haven't really looked into why), and the FreeBSD one just isn't
very good. But even the FreeBSD one appears to append primary weights
(only) to the blob it returns, and so is essentially the same for my
purposes [1].

[1] http://lists.freebsd.org/pipermail/freebsd-current/2003-April/001273.html
--
Peter Geoghegan