com.strobel.core.HashUtilities Maven / Gradle / Ivy
/*
* HashUtilities.java
*
* Copyright (c) 2012 Mike Strobel
*
* This source code is subject to terms and conditions of the Apache License, Version 2.0.
* A copy of the license can be found in the License.html file at the root of this distribution.
* By using this source code in any fashion, you are agreeing to be bound by the terms of the
* Apache License, Version 2.0.
*
* You must not remove this notice, or any other, from this software.
*/
package com.strobel.core;
import java.util.Arrays;
import java.util.List;
/**
* @author strobelm
*/
public final class HashUtilities {
public static final int NullHashCode = 0x61E04917;
private static final int HashPrime = 101;
private static final int CombinedHashOffset = 5;
private final static int MaxPrimeArrayLength = 0x7FEFFFFD;
private HashUtilities() {
throw new UnsupportedOperationException();
}
public static int hashCode(final Object o) {
if (o == null) {
return NullHashCode;
}
if (o.getClass().isArray()) {
if (o instanceof Object[]) {
return combineHashCodes((Object[]) o);
}
if (o instanceof byte[]) {
return Arrays.hashCode((byte[]) o);
}
if (o instanceof short[]) {
return Arrays.hashCode((short[]) o);
}
if (o instanceof int[]) {
return Arrays.hashCode((int[]) o);
}
if (o instanceof long[]) {
return Arrays.hashCode((long[]) o);
}
if (o instanceof char[]) {
return Arrays.hashCode((char[]) o);
}
if (o instanceof float[]) {
return Arrays.hashCode((float[]) o);
}
if (o instanceof double[]) {
return Arrays.hashCode((double[]) o);
}
if (o instanceof boolean[]) {
return Arrays.hashCode((boolean[]) o);
}
}
return o.hashCode();
}
public static int hashItems(final Iterable items) {
int hash = 0;
for (final Object o : items) {
hash <<= CombinedHashOffset;
hash ^= hashCode(o);
}
return hash;
}
public static int combineHashCodes(final int... hashes) {
int hash = 0;
for (final int h : hashes) {
hash <<= CombinedHashOffset;
hash ^= h;
}
return hash;
}
public static int combineHashCodes(final Object... objects) {
int hash = 0;
for (final Object o : objects) {
int entryHash = NullHashCode;
if (o != null) {
if (o instanceof Object[]) {
entryHash = combineHashCodes((Object[])o);
}
else {
entryHash = hashCode(o);
}
}
hash <<= CombinedHashOffset;
hash ^= entryHash;
}
return hash;
}
public static int combineHashCodes(final int hash1, final int hash2) {
return (hash1 << CombinedHashOffset) ^ hash2;
}
public static int combineHashCodes(final int hash1, final int hash2, final int hash3) {
return (((hash1 << CombinedHashOffset)
^ hash2) << CombinedHashOffset)
^ hash3;
}
public static int combineHashCodes(final int hash1, final int hash2, final int hash3, final int hash4) {
return (((((hash1 << CombinedHashOffset)
^ hash2) << CombinedHashOffset)
^ hash3) << CombinedHashOffset)
^ hash4;
}
public static int combineHashCodes(
final int hash1,
final int hash2,
final int hash3,
final int hash4,
final int hash5) {
return (((((((hash1 << CombinedHashOffset)
^ hash2) << CombinedHashOffset)
^ hash3) << CombinedHashOffset)
^ hash4) << CombinedHashOffset)
^ hash5;
}
public static int combineHashCodes(
final int hash1,
final int hash2,
final int hash3,
final int hash4,
final int hash5,
final int hash6) {
return (((((((((hash1 << CombinedHashOffset)
^ hash2) << CombinedHashOffset)
^ hash3) << CombinedHashOffset)
^ hash4) << CombinedHashOffset)
^ hash5) << CombinedHashOffset)
^ hash6;
}
public static int combineHashCodes(
final int hash1,
final int hash2,
final int hash3,
final int hash4,
final int hash5,
final int hash6,
final int hash7) {
return (((((((((((hash1 << CombinedHashOffset)
^ hash2) << CombinedHashOffset)
^ hash3) << CombinedHashOffset)
^ hash4) << CombinedHashOffset)
^ hash5) << CombinedHashOffset)
^ hash6) << CombinedHashOffset)
^ hash7;
}
public static int combineHashCodes(
final int hash1,
final int hash2,
final int hash3,
final int hash4,
final int hash5,
final int hash6,
final int hash7,
final int hash8) {
return (((((((((((((hash1 << CombinedHashOffset)
^ hash2) << CombinedHashOffset)
^ hash3) << CombinedHashOffset)
^ hash4) << CombinedHashOffset)
^ hash5) << CombinedHashOffset)
^ hash6) << CombinedHashOffset)
^ hash7) << CombinedHashOffset)
^ hash8;
}
public static int combineHashCodes(final Object o1, final Object o2) {
return combineHashCodes(
o1 == null ? NullHashCode : hashCode(o1),
o2 == null ? NullHashCode : hashCode(o2)
);
}
public static int combineHashCodes(final Object o1, final Object o2, final Object o3) {
return combineHashCodes(
o1 == null ? NullHashCode : hashCode(o1),
o2 == null ? NullHashCode : hashCode(o2),
o3 == null ? NullHashCode : hashCode(o3)
);
}
public static int combineHashCodes(final Object o1, final Object o2, final Object o3, final Object o4) {
return combineHashCodes(
o1 == null ? NullHashCode : hashCode(o1),
o2 == null ? NullHashCode : hashCode(o2),
o3 == null ? NullHashCode : hashCode(o3),
o4 == null ? NullHashCode : hashCode(o4)
);
}
public static int combineHashCodes(
final Object o1,
final Object o2,
final Object o3,
final Object o4,
final Object o5) {
return combineHashCodes(
o1 == null ? NullHashCode : hashCode(o1),
o2 == null ? NullHashCode : hashCode(o2),
o3 == null ? NullHashCode : hashCode(o3),
o4 == null ? NullHashCode : hashCode(o4),
o5 == null ? NullHashCode : hashCode(o5)
);
}
public static int combineHashCodes(
final Object o1,
final Object o2,
final Object o3,
final Object o4,
final Object o5,
final Object o6) {
return combineHashCodes(
o1 == null ? NullHashCode : hashCode(o1),
o2 == null ? NullHashCode : hashCode(o2),
o3 == null ? NullHashCode : hashCode(o3),
o4 == null ? NullHashCode : hashCode(o4),
o5 == null ? NullHashCode : hashCode(o5),
o6 == null ? NullHashCode : hashCode(o6)
);
}
public static int combineHashCodes(
final Object o1,
final Object o2,
final Object o3,
final Object o4,
final Object o5,
final Object o6,
final Object o7) {
return combineHashCodes(
o1 == null ? NullHashCode : hashCode(o1),
o2 == null ? NullHashCode : hashCode(o2),
o3 == null ? NullHashCode : hashCode(o3),
o4 == null ? NullHashCode : hashCode(o4),
o5 == null ? NullHashCode : hashCode(o5),
o6 == null ? NullHashCode : hashCode(o6),
o7 == null ? NullHashCode : hashCode(o7)
);
}
public static int combineHashCodes(
final Object o1,
final Object o2,
final Object o3,
final Object o4,
final Object o5,
final Object o6,
final Object o7,
final Object o8) {
return combineHashCodes(
o1 == null ? NullHashCode : hashCode(o1),
o2 == null ? NullHashCode : hashCode(o2),
o3 == null ? NullHashCode : hashCode(o3),
o4 == null ? NullHashCode : hashCode(o4),
o5 == null ? NullHashCode : hashCode(o5),
o6 == null ? NullHashCode : hashCode(o6),
o7 == null ? NullHashCode : hashCode(o7),
o8 == null ? NullHashCode : hashCode(o8)
);
}
// Table of prime numbers to use as hash table sizes.
// A typical resize algorithm would pick the smallest prime number in this array
// that is larger than twice the previous capacity.
// Suppose our Hashtable currently has capacity x and enough elements are added
// such that a resize needs to occur. Resizing first computes 2x then finds the
// first prime in the table greater than 2x, i.e. if primes are ordered
// p_1, p_2, ..., p_i, ..., it finds p_n such that p_n-1 < 2x < p_n.
// Doubling is important for preserving the asymptotic complexity of the
// hashtable operations such as add. Having a prime guarantees that double
// hashing does not lead to infinite loops. IE, your hash function will be
// h1(key) + i*h2(key), 0 <= i < size. h2 and the size must be relatively prime.
private final static int[] Primes = {
3, 7, 11, 17, 23, 29, 37, 47, 59, 71, 89, 107, 131, 163, 197, 239, 293, 353, 431, 521, 631, 761, 919,
1103, 1327, 1597, 1931, 2333, 2801, 3371, 4049, 4861, 5839, 7013, 8419, 10103, 12143, 14591,
17519, 21023, 25229, 30293, 36353, 43627, 52361, 62851, 75431, 90523, 108631, 130363, 156437,
187751, 225307, 270371, 324449, 389357, 467237, 560689, 672827, 807403, 968897, 1162687, 1395263,
1674319, 2009191, 2411033, 2893249, 3471899, 4166287, 4999559, 5999471, 7199369
};
public static boolean isPrime(final int candidate) {
if ((candidate & 1) != 0) {
final int limit = (int)Math.sqrt(candidate);
for (int divisor = 3; divisor <= limit; divisor += 2) {
if ((candidate % divisor) == 0) {
return false;
}
}
return true;
}
return (candidate == 2);
}
public static int getPrime(final int min) {
VerifyArgument.isNonNegative(min, "min");
for (final int prime : Primes) {
if (prime >= min) {
return prime;
}
}
//outside of our predefined table.
//compute the hard way.
for (int i = (min | 1); i < Integer.MAX_VALUE; i += 2) {
if (isPrime(i) && ((i - 1) % HashPrime != 0)) {
return i;
}
}
return min;
}
public static int getMinPrime() {
return Primes[0];
}
public static int expandPrime(final int oldSize) {
final int newSize = 2 * oldSize;
// Allow the hashtables to grow to maximum possible size (~2G elements) before encoutering capacity overflow.
// Note that this check works even when _items.Length overflowed thanks to the (uint) cast
if (Math.abs(newSize) > MaxPrimeArrayLength && MaxPrimeArrayLength > oldSize) {
assert MaxPrimeArrayLength == getPrime(MaxPrimeArrayLength) : "Invalid MaxPrimeArrayLength";
return MaxPrimeArrayLength;
}
return getPrime(newSize);
}
}
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