On Tuesday, June 18, 2013 4:05:25 PM UTC-4, Antoine Pitrou wrote:
> One invokes a fast special-purpose substring searching routine (the
> str.__contains__ operator), the other a generic matching engine able to
> process complex patterns. It's hardly a surprise for the specialized routine
> to be faster.
Except that the complexity in regexes is compiling the pattern down to a FSM.
Once you've got the FSM built, the inner loop should be pretty quick. In C, the
inner loop for executing a FSM should be something like:
for(char* p = input; p; ++p) {
next_state = current_state[*p];
if (next_state == MATCH) {
break;
}
}
which should compile down to a couple of machine instructions which run
entirely in the instruction pipeline cache. But I'm probably simplifying it
more than I should :-)
> (to be fair, on CPython there's also the fact that operators are faster
> than method calls, so some overhead is added by that too)
I've been doing some experimenting, and I'm inclined to believe this is indeed
a significant part of it. I also took some ideas from André Malo and factored
out some name lookups from the inner loop. That bummed me another 10% in speed.
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