GNU grep 2.17, 10x faster (lists.gnu.org)

Someone knows how was this achieved?

From the NEWS section in the page:

Improvements

  grep -i in a multibyte locale is now typically 10 times faster
  for patterns that do not contain \ or [.

  grep (without -i) in a multibyte locale is now up to 7 times faster
  when processing many matched lines.

taken from http://git.savannah.gnu.org/gitweb/?p=grep.git;a=commit;h=97... it seems like the speedup was achieved in the most common case of usage, which is with the -i switch (for case insensitive searching).

taken from the commit log:

"The trick is to realize that for some search strings, it is easy to convert to an equivalent one that is handled much more efficiently. E.G. convert this command:

  grep -i foobar k

to this:

  grep '[fF][oO][oO][bB][aA][rR]' k

That allows the matcher to search in buffer mode, rather than having to extract/case-convert/search each line separately. Currently, we perform this conversion only when search strings contain neither '\' nor '['."