timezone.el patterns in emacs 19.34

[Ken Raeburn <raeburn@cygnus.com>]

FYI, in case anyone wants to try out this change...

------- Start of forwarded message -------
Date: Fri, 2 May 1997 04:44:11 -0400
Message-Id: <199705020844.EAA06520@kr-laptop.cygnus.com>
From: Ken Raeburn <raeburn@cygnus.com>
To: umerin@mse.kyutech.ac.jp, rms@gnu.ai.mit.edu
Subject: timezone.el patterns in emacs 19.34


I noticed some time ago that timezone-parse-date took up a large
portion of the time of building a summary buffer in Gnus.  Tonight I
did a little instrumenting of that routine.  If my results are
correct, all the mail headers I've processed since (over 12000) *all*
matched one of the regexp patterns, namely the one labeled

	   ;; Styles: (1) and (2) with timezone and buggy timezone

which means basically

	[wkday,] DD MMM YYYY hh:mm[:ss] [TZ]

This looks like the right form for news headers as well.

This is the fourth regexp to be tried.  The first two are looking for:

	wkday, DD MMM hh:mm:ss [T] YYYY [TZ]

with and without the timezone specification; I haven't seen this form
actually match anything.  The third regexp checked is styles 1/2
without the timezone.

Blindly assuming that the regexps are all mutually exclusive in the
strings they'll match, I moved this one to the top of the `cond'
expression for some timing tests, using some data from my mail
headers.  The speed improvement (testing just the inner guts of
timezone-parse-date, without the code for stripping text properties)
was about a factor of 2.5.

So if it is in fact safe, I think it'd be worth moving this pattern to
the top of the list.

Does anything else use timezone-parse-date so intensely, that might
"prefer" the order used now?

Ken

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