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bug#35708: [27.0.50]: thingatpt.el, thing-at-point-looking-at redundant


From: Andreas Röhler
Subject: bug#35708: [27.0.50]: thingatpt.el, thing-at-point-looking-at redundant
Date: Wed, 15 May 2019 08:59:19 +0200
User-agent: Mozilla/5.0 (X11; Linux i686; rv:60.0) Gecko/20100101 Thunderbird/60.6.1


Am 14.05.19 um 16:34 schrieb address@hidden:
Andreas Röhler <address@hidden> writes:

Hmm, current thing-at-point-looking-at might be slow with large
buffers. The slightly modified test should reveal it:

(ert-deftest thing-at-point-looking-at-2 ()
   (with-temp-buffer
     (insert "1abcd 222abcd")
     (dotimes (_ 99999) (insert " asdf "))
     (goto-char (point-min))
       (search-forward "2ab")
       (should (thing-at-point-looking-at "2abcd"))
Yes, in this case, since the loop over looking-at only needs to iterate
twice, so it will be faster.  But what about when there is no match?
E.g.,

(with-temp-buffer
   (dotimes (_ 99999) (insert " asdf "))
   (goto-char (point-max))
   (list :ar-regexp-atpt (benchmark-run (ar-regexp-atpt "foo"))
         :thing-at-point-looking-at (benchmark-run (thing-at-point-looking-at 
"foo"))))

Another fix, as a bug showed up when testing (ar-regexp-atpt "[a-z]+"):

(defun ar-regexp-atpt (regexp)
   "Return t if REGEXP matches at or before point, nil otherwise.

Changes match-data"
   (save-excursion
     (if (looking-at regexp)
     (while
         (and (not (bobp))
          (or (progn (backward-char) (looking-at regexp))
              (forward-char 1))))
       (while (not (or (bobp) (backward-char) (looking-at regexp))))
       (ar-regexp-atpt regexp))
What's this recursive call for?  It triggers (error "Lisp nesting
exceeds ‘max-lisp-eval-depth’") in the benchmark above.

     (looking-at regexp)))


The recursive call needed a guard:     (unless (bobp)

It is called after function went backward while not looking-at matches,

Now the result for the 99999 is

(:ar-regexp-atpt (0.774574453 0 0.0) :thing-at-point-looking-at (0.000798669 0 0.0))


The fixed form:

(defun ar-regexp-atpt (regexp)
  "Return t if REGEXP matches at or before point, nil otherwise.

Changes match-data"
  (save-excursion
    (if (looking-at regexp)
    (while
        (and (not (bobp))
         (or (progn (backward-char) (looking-at regexp))
             (forward-char 1))))
      (while (not (or (bobp) (backward-char) (looking-at regexp))))
      (unless (bobp) (ar-regexp-atpt regexp)))
    (looking-at regexp)))







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