Le 11/11/2012 12:38, Manfred Nowak a écrit :
Jakse wrote:
It would also be interesting to have ideas for the general
case
Yes, ideas might be interesting. :-)
A root of "good" hashing is incorporated in algorithm2 of your
posting:
spread the values produced by the hash function uniformly over
the interval size_t.min .. size_t.max.
Therefore:
Compute the hash value for a given key by multiplying each byte
of the key with a factor, which increases from the byte with
lowest significance to the byte with highest significance; of
course add the results.
Remarks:
a)
Because of the general case: assume that the original key
contains much redundance. Therefore do not use the bytes of the
original key but compute a ( at least close to) lossless
compression of the original key.
b)
The factors in the factor list should be primes for spreading
the hash value uniformly over the intended range
c)
The quotint of two consecutives primes in the factor list should
be greater than 256, because the used key might not contain any
reduundancy.
-manfred
Thanks for this interesting answer.
Is compressing for performance reasons ? is it more interesting to
compress and then hash than just hash ?
