In-Reply-To: <018201c52567$1b710ca0$6601a8c0@pdimov> pdimov@mmltd.net (Peter Dimov) wrote (abridged):

But as I said, benchmarking hash functions is pointless. Real programs do not compute the hash value of a random 256 byte buffer five million times. They usually need to do something with the hash value. This something typically involves a division on a prime to obtain a modulus, several pointer chasings, and at least one equality comparison (which on a 256 byte buffer will have considerable impact).

I'd add that my own application caches the results of the hash at highish level, so it doesn't actually matter that much if it is slow. The equality comparison is only needed if the hashes are equal. If you are doing something like adding values to a set, and all the values are in fact different, then hopefully the hashes will be different and the equality tests never needed. In my own code I use a mixture of hashing and interning. This means that if objects are equal they probably have the same address. If they are different they probably have different (cached) hashes. Full byte-by-byte compares of all the data are rarely needed. -- Dave Harris, Nottingham, UK