com.uwyn.jhighlight.pcj.hash

Class Primes

java.lang.Object

com.uwyn.jhighlight.pcj.hash.Primes

public class Primes
extends java.lang.Object

This class provides a static table of int sized prime numbers. For small numbers (0-511) it contains all primes. For larger numbers it contains 32 primes each time the number of bits is increased. I.e., there are 32 primes from 512 to 1023, 32 primes from 1024 to 2048, etc., the primes thus becoming less dense with size. Within the interval formed by using one more bit (say, v0 to v1), the 32 primes are formed by searching for the first prime greater than or equal to v0 + n*(v1-v0)/32, n belonging to {0,1,2, ..., 31}. This creates a reasonable distribution.

Since:

1.0

Version:

1.2 21-08-2003 20:21

Field Summary

Fields

Modifier and Type	Field and Description
private static int[]	primes Prime numbers in ascending order.

Constructor Summary

Constructors

Modifier	Constructor and Description
private	Primes() Prevents instantiation.

Method Summary

Modifier and Type	Method and Description
static int	nextPrime(int n) Returns from a static prime table the least prime that is greater than or equal to a specified value.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

primes

private static final int[] primes

Prime numbers in ascending order.

Constructor Detail

Primes

private Primes()

Prevents instantiation.

Method Detail

nextPrime

public static int nextPrime(int n)

Returns from a static prime table the least prime that is greater than or equal to a specified value. On average, the returned prime will about 1/64 of 2^(r+1) - 2^r greater than n, where r is the order of n (the number of bits required for representing it).

Returns:

the least prime in the table that is greater than or equal to the specified value.