On Jun 30, 2009, at 9:57 AM, Patrick Hanna wrote:
I have noticed that rather than using memcmp for comparing strings, webkit likes to cast to uint32_t* and compare in a for loop. For example, WebCore::equal in AtomicString.cpp and StringHash::equal in StringHash.h. Is there any reason not to memcmp? I am assuming that most implementations of memcmp will do the word alignment and basically do the same thing.
We found the copy loop to be a little bit faster than memcmp on the platforms where we tested. memcmp tends not to do as well for short strings because it doesn't know that the start and end have some alignment guarantees. Also there is the function call overhead.
The reason I ask is because StringHash::equal does not check for PLATFORM(ARM) or PLATFORM(SH4) so I was going to submit a patch to use memcmp for ARM/SH4 but didn't know if that was frowned upon (and WebCore::equal does a loop for ARM/SH4 as well).
Is there a reason you'd want to make the code use a different implementation depending on the CPU? (It's not obvious to me from your message).
Regards, Maciej _______________________________________________ webkit-dev mailing list [email protected] http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
