Can anybody explain the logic behind the use of djb2 hash function as a good option for strings. The algorithm can be found at http://www.cse.yorku.ca/~oz/hash.html
Why is it that 5381 and 33 hold such an importance in djb2 algorithm ???
Thanks, De Costo
Maybe because 33 == 2^5 + 1 and many hashing algorithms use 2^n + 1 as their multiplier?
Credit to Jerome Berger
Update:
This seems to be borne out by the current version of the software package djb2 originally came from: cdb
The notes I linked to describe the heart of the hashing algorithm as using h = ((h << 5) + h) ^ c to do the hashing... x << 5 is a fast hardware way to use 2^5 as the multiplier.
On 5381, Dan Bernstein (djb2) says in this article:
[...] practically any good multiplier works. I think you're worrying about the fact that 31c + d doesn't cover any reasonable range of hash values if c and d are between 0 and 255. That's why, when I discovered the 33 hash function and started using it in my compressors, I started with a hash value of 5381. I think you'll find that this does just as well as a 261 multiplier.
The whole thread is here if you're interested.
Ozan Yigit has a page on hash functions which says:
[...] the magic of number 33 (why it works better than many other constants, prime or not) has never been adequately explained.