Package org.wildfly.common.math

Class HashMath

java.lang.Object
org.wildfly.common.math.HashMath
public final class HashMath extends Object
Routines which are useful for hashcode computation, among other things.
Author:
David M. Lloyd

  • Method Summary

    Modifier and Type
    Method
    Description
    static int
    multiHashOrdered(int accumulatedHash, int nextHash)
    A hash function which combines an accumulated hash with a next hash such that f(f(k, b), a) ≠ₙ f(f(k, a), b).
    static int
    multiHashOrdered(int accumulatedHash, int prime, int nextHash)
    A hash function which combines an accumulated hash with a next hash such that f(f(k, p2, b), p1, a) ≠ₙ f(f(k, p1, a), p2, b).
    static int
    multiHashUnordered(int accumulatedHash, int nextHash)
    A hash function which combines an accumulated hash with a next hash such that f(f(k, b), a) = f(f(k, a), b).
    static int
    multiHashUnordered(int accumulatedHash, int prime, int nextHash)
    A hash function which combines an accumulated hash with a next hash such that f(f(k, p2, b), p1, a) = f(f(k, p1, a), p2, b).
    static int
    multiplyWrap(int a, int b)
    Multiply two unsigned integers together.
    static int
    roundToPowerOfTwo(int value)
    Round the given value up to the next positive power of two.

    Methods inherited from class java.lang.Object

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

  • Method Details

    • roundToPowerOfTwo

      public static int roundToPowerOfTwo(int value)
      Round the given value up to the next positive power of two.
      Parameters:
      value - the value (must not be negative and must be less than or equal to 2^31)
      Returns:
      the rounded power of two value

    • multiHashOrdered

      public static int multiHashOrdered(int accumulatedHash, int prime, int nextHash)
      A hash function which combines an accumulated hash with a next hash such that f(f(k, p2, b), p1, a) ≠ₙ f(f(k, p1, a), p2, b). This function is suitable for object chains whose order affects the overall equality of the hash code.

      The exact algorithm is not specified and is therefore subject to change and should not be relied upon for hash codes that persist outside of the JVM process.

      Parameters:
      accumulatedHash - the accumulated hash code of the previous stage
      prime - a prime multiplier
      nextHash - the hash code of the next single item
      Returns:
      the new accumulated hash code

    • multiHashUnordered

      public static int multiHashUnordered(int accumulatedHash, int prime, int nextHash)
      A hash function which combines an accumulated hash with a next hash such that f(f(k, p2, b), p1, a) = f(f(k, p1, a), p2, b). This function is suitable for object chains whose order does not affect the overall equality of the hash code.

      The exact algorithm is not specified and is therefore subject to change and should not be relied upon for hash codes that persist outside of the JVM process.

      Parameters:
      accumulatedHash - the accumulated hash code of the previous stage
      prime - a prime multiplier
      nextHash - the hash code of the next single item
      Returns:
      the new accumulated hash code

    • multiHashOrdered

      public static int multiHashOrdered(int accumulatedHash, int nextHash)
      A hash function which combines an accumulated hash with a next hash such that f(f(k, b), a) ≠ₙ f(f(k, a), b). This function is suitable for object chains whose order affects the overall equality of the hash code.

      The exact algorithm is not specified and is therefore subject to change and should not be relied upon for hash codes that persist outside of the JVM process.

      Parameters:
      accumulatedHash - the accumulated hash code of the previous stage
      nextHash - the hash code of the next single item
      Returns:
      the new accumulated hash code

    • multiHashUnordered

      public static int multiHashUnordered(int accumulatedHash, int nextHash)
      A hash function which combines an accumulated hash with a next hash such that f(f(k, b), a) = f(f(k, a), b). This function is suitable for object chains whose order does not affect the overall equality of the hash code.

      The exact algorithm is not specified and is therefore subject to change and should not be relied upon for hash codes that persist outside of the JVM process.

      Parameters:
      accumulatedHash - the accumulated hash code of the previous stage
      nextHash - the hash code of the next single item
      Returns:
      the new accumulated hash code

    • multiplyWrap

      public static int multiplyWrap(int a, int b)
      Multiply two unsigned integers together. If the result overflows a 32-bit number, XOR the overflowed bits back into the result. This operation is commutative, i.e. if we designate the ⨰ symbol to represent this operation, then a ⨰ b = b ⨰ a. This operation is not associative, i.e. (a ⨰ b) ⨰ c ≠ₙ a ⨰ (b ⨰ c) (the symbol ≠ₙ meaning "not necessarily equal to"), therefore this operation is suitable for ordered combinatorial hash functions.
      Parameters:
      a - the first number to multiply
      b - the second number to multiply
      Returns:
      the wrapped multiply result