c r <[EMAIL PROTECTED]> wrote:Thanks for replying!
Thomas Bätzler <[EMAIL PROTECTED]> wrote: Hi, c r asked: > I need to match an expression and its reverse to a very long string. > When a match occurs all matching should stop and the position > of the match should be returned. Could you please illustrate this with an example or two? Don't mind the lack of position return. I have: $expres = '10_normal_characters'; $rev_expres = reverse $expres; $long_string = 'ARGBB...........'; if ($long_string =~ /$expres/i) { next;} if ($long_string =~ /$rev_expres/i) {next;} (the "next" function takes a different $expres reverses it and does the matching procedure again. This is repeted many thounsands of times and it takes days to finish). Unless you specify the /g modifier, the RE engine stops at the first match. Use the pos function to find the position of the match. > Question1: can I match the forward and reverse expression to > the string on the same time and thereby save half the time it > normally would take to find a match or does the matching just > get slower? Well, you'd have to merge your expressions somehow - the easiest way would be to try and match /expr-a|expr-b/ but then I suspect that for all but simple cases two separate matches would be faster. > Question2: is the "fork" function what I should use in order > to match a string with multiple expressions simultaneously? Well, there is a certain overhead involved in keeping your processes synchronized that would only be outweighed if you had a multi CPU machine where both processes could run at once in the first place. Even then it's a hassle. So in order to match a very long string with multiple expressions simultaneously and faster than the matching procedure I have described above I need multiple computers? If I were you I'd focus my energy in optimizing the expression. If you're going to match many long strings with the same RE, you could use the /o modifier to benefit. Also, you could try wether a study() of the input strings speeds things up. I don't know the "study" function, but I doubt it can solve the problem to satisfatory. please correct me if I am wrong! I acknowledge that this is a serious programming challenge. Do you have any other ideas of how to tackle this problem (what about other hardware)? HTH, Thomas