comment on

That is a veru inefficient version of /a*b/ which is likely to do a vast amount of backtracking!

Update: interesting that if you remove the character class it goes very much faster. It forces backtracking where the non-character class variant manages to fail immediately.

C:\junk>perl noname.pl
Compiling REx `a*b'
size 6 Got 52 bytes for offset annotations.
first at 1
synthetic stclass `ANYOF[ab]'.
   1: STAR(4)
   2:   EXACT <a>(0)
   4: EXACT <b>(6)
   6: END(0)
floating `b' at 0..2147483647 (checking floating) stclass `ANYOF[ab]' 
+minlen 1
Offsets: [6]
        2[1] 1[1] 0[0] 3[1] 0[0] 4[0]
Guessing start of match, REx `a*b' against `aaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa...'...
Did not find floating substr `b'...
Match rejected by optimizer
Hello
Freeing REx: `"a*b"'

C:\junk>perl noname.pl
Compiling REx `a*[b]'
size 15 Got 124 bytes for offset annotations.
first at 1
synthetic stclass `ANYOF[ab]'.
   1: STAR(4)
   2:   EXACT <a>(0)
   4: ANYOF[b](15)
  15: END(0)
stclass `ANYOF[ab]' minlen 1
Offsets: [15]
        2[1] 1[1] 0[0] 3[3] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[0] 0[
+0] 0[0] 6[0]
Matching REx `a*[b]' against `aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaa...'
Matching stclass `ANYOF[ab]' against `aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaa'
  Setting an EVAL scope, savestack=3
   0 <> <aaaaaaaaaaaa>    |  1:  STAR
                           EXACT <a> can match 61 times out of 2147483
+647...
  Setting an EVAL scope, savestack=3
  61 <aaaaaaaaaaaa> <>    |  4:    ANYOF[b]
                              failed...
  60 <aaaaaaaaaaa> <a>    |  4:    ANYOF[b]
                              failed...
  59 <aaaaaaaaaa> <aa>    |  4:    ANYOF[b]
                              failed...
  58 <aaaaaaaaa> <aaa>    |  4:    ANYOF[b]
                              failed...
  57 <aaaaaaaa> <aaaa>    |  4:    ANYOF[b]
                              failed...
  56 <aaaaaaa> <aaaaa>    |  4:    ANYOF[b]
                              failed...
  55 <aaaaaa> <aaaaaa>    |  4:    ANYOF[b]
                              failed...
  54 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  53 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  52 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  51 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  50 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  49 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  48 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  47 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  46 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  45 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  44 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  43 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  42 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  41 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  40 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  39 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  38 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  37 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  36 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  35 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  34 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  33 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  32 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  31 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  30 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  29 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  28 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  27 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  26 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  25 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  24 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  23 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  22 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  21 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  20 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  19 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  18 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  17 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  16 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  15 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  14 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  13 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  12 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  11 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
  10 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
   9 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
   8 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
   7 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
   6 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
   5 <aaaaa> <aaaaaaa>    |  4:    ANYOF[b]
                              failed...
   4 <aaaa> <aaaaaaaa>    |  4:    ANYOF[b]
                              failed...
   3 <aaa> <aaaaaaaaa>    |  4:    ANYOF[b]
                              failed...
   2 <aa> <aaaaaaaaaa>    |  4:    ANYOF[b]
                              failed...
   1 <a> <aaaaaaaaaaa>    |  4:    ANYOF[b]
                              failed...
   0 <> <aaaaaaaaaaaa>    |  4:    ANYOF[b]
                              failed...
                            failed...
  Setting an EVAL scope, savestack=3
   1 <a> <aaaaaaaaaaa>    |  1:  STAR
                           EXACT <a> can match 60 times out of 2147483
+647...
  Setting an EVAL scope, savestack=3

... # much similar stuff omitted

EXACT <a> can match 2 times out of 2147483647...
  Setting an EVAL scope, savestack=3
  61 <aaaaaaaaaaaa> <>    |  4:    ANYOF[b]
                              failed...
  60 <aaaaaaaaaaa> <a>    |  4:    ANYOF[b]
                              failed...
  59 <aaaaaaaaaa> <aa>    |  4:    ANYOF[b]
                              failed...
                            failed...
  Setting an EVAL scope, savestack=3
  60 <aaaaaaaaaaa> <a>    |  1:  STAR
                           EXACT <a> can match 1 times out of 21474836
+47...
  Setting an EVAL scope, savestack=3
  61 <aaaaaaaaaaaa> <>    |  4:    ANYOF[b]
                              failed...
  60 <aaaaaaaaaaa> <a>    |  4:    ANYOF[b]
                              failed...
                            failed...
Contradicts stclass...
Match failed
Hello
Freeing REx: `"a*[b]"'
[download]

DWIM is Perl's answer to Gödel

In reply to Re: slow regular expressions by GrandFather
in thread slow regular expressions by jesuashok

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