DFA trys to find a long sequence of characters that must appear in any line containing the r.e. in dfamust() However, if a pattern is long, it is very slow, as it processes all characters step by step. This change makes a string concatenated some normal characters process at a time.
Following test case is posted in bug#15191. It speeds-up more than 60x. http://debbugs.gnu.org/cgi/bugreport.cgi?bug=15191#5 << before changed >> $ time -p grep -f regex.re input_lines.txt real 1.28 user 1.27 sys 0.00 << after changed >> $ time -p grep -f regex.re input_lines.txt real 0.02 user 0.01 sys 0.00
0001-dfa-speed-up-for-long-pattern.patch
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