What is the fastest hash algorithm to check if two files are equal?

Question

What is the fastest way to create a hash function which will be used to check if two files are equal?

Security is not very important.

Edit: I am sending a fi

Answer 1

xxhash purports itself as quite fast and strong, collision-wise:

http://cyan4973.github.io/xxHash/

There is a 64 bit variant that runs "even faster" on 64 bit processors than the 32, overall, though slower on 32-bit processors (go figure).

http://code.google.com/p/crcutil is also said to be quite fast (and leverages hardware CRC instructions where present, which are probably very fast, but if you don't have hardware that supports them, aren't as fast). Don't know if CRC32c is as good of a hash (in terms of collisions) as xxHash or not...

https://code.google.com/p/cityhash/ seems similar and related to crcutil [in that it can compile down to use hardware CRC32c instructions if instructed].

If you "just want the fastest raw speed" and don't care as much about quality of random distribution of the hash output (for instance, with small sets, or where speed is paramount), there are some fast algorithms mentioned here: http://www.sanmayce.com/Fastest_Hash/ (these "not quite random" distribution type algorithms are, in some cases, "good enough" and very fast). Apparently FNV1A_Jesteress is the fastest for "long" strings, some others possibly for small strings. http://locklessinc.com/articles/fast_hash/ also seems related. I did not research to see what the collision properties of these are.