Package mondrian.util

Class PrimeFinder


  • final class PrimeFinder
    extends Object
    Not of interest for users; only for implementors of hashtables. Used to keep hash table capacities prime numbers.

    Choosing prime numbers as hash table capacities is a good idea to keep them working fast, particularly under hash table expansions.

    However, JDK 1.2, JGL 3.1 and many other toolkits do nothing to keep capacities prime. This class provides efficient means to choose prime capacities.

    Choosing a prime is O(log 300) (binary search in a list of 300 int's). Memory requirements: 1 KB static memory.

    Version:
    1.0, 09/24/99
    Author:
    wolfgang.hoschek@cern.ch
    • Field Detail

      • largestPrime

        public static final int largestPrime
        The largest prime this class can generate; currently equal to Integer.MAX_VALUE. yes, it is prime.
        See Also:
        Constant Field Values
    • Method Detail

      • nextPrime

        public static int nextPrime​(int desiredCapacity)
        Returns a prime number which is >= desiredCapacity and very close to desiredCapacity (within 11% if desiredCapacity >= 1000).
        Parameters:
        desiredCapacity - the capacity desired by the user.
        Returns:
        the capacity which should be used for a hashtable.
      • main

        protected static void main​(String[] args)
        Tests correctness. Try from=1000, to=10000 from=200, to=1000 from=16, to=1000 from=1000, to=Integer.MAX_VALUE
      • statistics

        protected static void statistics​(int from,
                                         int to,
                                         PrintWriter pw)
        Tests correctness.