Editing Double hashing (section)

== Selection of h<sub>2</sub>(k)==
The secondary hash function <math>h_2(k)</math> should have several characteristics:
* It should never yield an index of zero.
* It should cycle through the whole table.
* It should be very fast to compute.
* It should be pair-wise independent of <math>h_1(k)</math>.
* The distribution characteristics of <math>h_2</math> are irrelevant. It is analogous to a random-number generator.
* All <math>h_2(k)</math> should be ''relatively prime'' to |''T''|.

In practice:
* If division hashing is used for both functions, the divisors are chosen as primes.
* If |''T''| is a power of 2, the first and last requirements are usually satisfied by making <math>h_2(k)</math> always return an odd number. This has the side effect of doubling the chance of collision due to one wasted bit.<ref name=Dillinger04/>