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In particular, if one uses dynamic resizing with exact doubling and halving of the table size, then the hash function needs to be uniform only when the size is a power of two. Here the index can be computed as some range of bits of the hash function. On the other hand, some hashing algorithms prefer to have the size be a prime number. [18]
It can be used directly as the hash code, or a hash function applied to it to map the potentially large value to the hash table size. The value of a is usually a prime number large enough to hold the number of different characters in the character set of potential keys.
The important performance parameters for perfect hashing are the representation size, the evaluation time, the construction time, and additionally the range requirement (average number of buckets per key in the hash table). [4] The evaluation time can be as fast as O(1), which is optimal.
The table below lists the largest currently known prime numbers and probable primes (PRPs) as tracked by the PrimePages and by Henri & Renaud Lifchitz's PRP Records. Numbers with more than 2,000,000 digits are shown.
Fowler–Noll–Vo (or FNV) is a non-cryptographic hash function created by Glenn Fowler, Landon Curt Noll, and Kiem-Phong Vo.. The basis of the FNV hash algorithm was taken from an idea sent as reviewer comments to the IEEE POSIX P1003.2 committee by Glenn Fowler and Phong Vo in 1991.
Let h(k) be a hash function that maps an element k to an integer in [0, m−1], where m is the size of the table. Let the i th probe position for a value k be given by the function (,) = + + where c 2 ≠ 0 (If c 2 = 0, then h(k,i) degrades to a linear probe
Another way to understand primary clustering is by examining the standard deviation on the number of items that hash to a given region within the hash table. [2] Consider a sub-region of the hash table of size x 2 {\displaystyle x^{2}} .
A prime sieve or prime number sieve is a fast type of algorithm for finding primes. There are many prime sieves. The simple sieve of Eratosthenes (250s BCE), the sieve of Sundaram (1934), the still faster but more complicated sieve of Atkin [1] (2003), sieve of Pritchard (1979), and various wheel sieves [2] are most common.