From: Junio C Hamano Date: Wed, 17 Jun 2009 16:42:43 GMT Subject: Re: [PATCH] avoid exponential regex match for java and objc function names Message-ID: <7vab46rev0.fsf@alter.siamese.dyndns.org> In-Reply-To: <1245248766-14867-1-git-send-email-bonzini@gnu.org> Paolo Bonzini writes: > In the old regex > > ^[ \t]*(([ \t]*[A-Za-z_][A-Za-z_0-9]*){2,}[ \t]*\([^;]*)$ > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > > you can backtrack arbitrarily from [A-Za-z_0-9]* into [A-Za-z_], thus > causing an exponential number of backtracks. Ironically it also causes > the regex not to work as intended; for example "catch" can match the > underlined part of the regex, the first repetition matching "c" and > the second matching "atch". > > The replacement regex avoids this problem, because it makes sure that > at least a space/tab is eaten on each repetition. In other words, > a suffix of a repetition can never be a prefix of the next repetition. Thanks; nicely done. Should I remove the "/* -- */" or is it for better readability I should keep? > Signed-off-by: Paolo Bonzini > --- > userdiff.c | 5 +++-- > 1 files changed, 3 insertions(+), 2 deletions(-) > > diff --git a/userdiff.c b/userdiff.c > index d556da9..57529ae 100644 > --- a/userdiff.c > +++ b/userdiff.c > @@ -13,7 +13,8 @@ PATTERNS("html", "^[ \t]*(<[Hh][1-6][ \t].*>.*)$", > "[^<>= \t]+|[^[:space:]]|[\x80-\xff]+"), > PATTERNS("java", > "!^[ \t]*(catch|do|for|if|instanceof|new|return|switch|throw|while)\n" > - "^[ \t]*(([ \t]*[A-Za-z_][A-Za-z_0-9]*){2,}[ \t]*\\([^;]*)$", > + "^[ \t]*(([A-Za-z_][A-Za-z_0-9]*[ \t]+)+[A-Za-z_][A-Za-z_0-9]*[ \t]*\\([^;]*)$", > + /* -- */ > "[a-zA-Z_][a-zA-Z0-9_]*" > "|[-+0-9.e]+[fFlL]?|0[xXbB]?[0-9a-fA-F]+[lL]?" > "|[-+*/<>%&^|=!]=" > @@ -25,7 +26,7 @@ PATTERNS("objc", > /* Objective-C methods */ > "^[ \t]*([-+][ \t]*\\([ \t]*[A-Za-z_][A-Za-z_0-9* \t]*\\)[ \t]*[A-Za-z_].*)$\n" > /* C functions */ > - "^[ \t]*(([ \t]*[A-Za-z_][A-Za-z_0-9]*){2,}[ \t]*\\([^;]*)$\n" > + "^[ \t]*(([A-Za-z_][A-Za-z_0-9]*[ \t]+)+[A-Za-z_][A-Za-z_0-9]*[ \t]*\\([^;]*)$\n" > /* Objective-C class/protocol definitions */ > "^(@(implementation|interface|protocol)[ \t].*)$", > /* -- */ > -- > 1.6.0.3