/* * Copyright (C) 2011 The Guava Authors * * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except * in compliance with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software distributed under the License * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express * or implied. See the License for the specific language governing permissions and limitations under * the License. */ package com.google.common.hash; import static com.google.common.base.Preconditions.checkArgument; import com.google.common.annotations.Beta; import com.google.common.annotations.VisibleForTesting; import com.google.common.base.Supplier; import java.nio.ByteBuffer; import java.security.MessageDigest; import java.util.Iterator; import java.util.zip.Adler32; import java.util.zip.CRC32; import java.util.zip.Checksum; /** * Static methods to obtain {@link HashFunction} instances, and other static hashing-related * utilities. * * @author Kevin Bourrillion * @author Dimitris Andreou * @author Kurt Alfred Kluever * @since 11.0 */ @Beta public final class Hashing { private Hashing() {} /** * Used to randomize {@link #goodFastHash} instances, so that programs which persist anything * dependent on hashcodes of those, will fail sooner than later. */ private static final int GOOD_FAST_HASH_SEED = (int) System.currentTimeMillis(); // Used by goodFastHash when minimumBits == 32. private static final HashFunction GOOD_FAST_HASH_FUNCTION_32 = murmur3_32(GOOD_FAST_HASH_SEED); // Used by goodFastHash when 32 < minimumBits <= 128. private static final HashFunction GOOD_FAST_HASH_FUNCTION_128 = murmur3_128(GOOD_FAST_HASH_SEED); /** * Returns a general-purpose, non-cryptographic-strength, streaming hash function that * produces hash codes of length at least {@code minimumBits}. Users without specific * compatibility requirements and who do not persist the hash codes are encouraged to * choose this hash function. * *
Repeated calls to {@link #goodFastHash} with the same {@code minimumBits} value will * return {@link HashFunction} instances with identical behavior (but not necessarily the * same instance) for the duration of the current virtual machine. * *
Warning: the implementation is unspecified and is subject to change. * * @throws IllegalArgumentException if {@code minimumBits} is not positive */ public static HashFunction goodFastHash(int minimumBits) { int bits = checkPositiveAndMakeMultipleOf32(minimumBits); if (bits == 32) { return GOOD_FAST_HASH_FUNCTION_32; } if (bits <= 128) { return GOOD_FAST_HASH_FUNCTION_128; } // Otherwise, join together some 128-bit murmur3s int hashFunctionsNeeded = (bits + 127) / 128; HashFunction[] hashFunctions = new HashFunction[hashFunctionsNeeded]; hashFunctions[0] = GOOD_FAST_HASH_FUNCTION_128; int seed = GOOD_FAST_HASH_SEED; for (int i = 1; i < hashFunctionsNeeded; i++) { seed += 1500450271; // a prime; shouldn't matter hashFunctions[i] = murmur3_128(seed); } return new ConcatenatedHashFunction(hashFunctions); } /** * Returns a hash function implementing the * * 32-bit murmur3 algorithm, x86 variant (little-endian variant), * using the given seed value. * *
The exact C++ equivalent is the MurmurHash3_x86_32 function (Murmur3A). */ public static HashFunction murmur3_32(int seed) { return new Murmur3_32HashFunction(seed); } /** * Returns a hash function implementing the * * 32-bit murmur3 algorithm, x86 variant (little-endian variant), * using a seed value of zero. * *
The exact C++ equivalent is the MurmurHash3_x86_32 function (Murmur3A). */ public static HashFunction murmur3_32() { return MURMUR3_32; } private static final HashFunction MURMUR3_32 = new Murmur3_32HashFunction(0); /** * Returns a hash function implementing the * * 128-bit murmur3 algorithm, x64 variant (little-endian variant), * using the given seed value. * *
The exact C++ equivalent is the MurmurHash3_x64_128 function (Murmur3F). */ public static HashFunction murmur3_128(int seed) { return new Murmur3_128HashFunction(seed); } /** * Returns a hash function implementing the * * 128-bit murmur3 algorithm, x64 variant (little-endian variant), * using a seed value of zero. * *
The exact C++ equivalent is the MurmurHash3_x64_128 function (Murmur3F). */ public static HashFunction murmur3_128() { return MURMUR3_128; } private static final HashFunction MURMUR3_128 = new Murmur3_128HashFunction(0); /** * Returns a hash function implementing the MD5 hash algorithm (128 hash bits) by delegating to * the MD5 {@link MessageDigest}. */ public static HashFunction md5() { return MD5; } private static final HashFunction MD5 = new MessageDigestHashFunction("MD5", "Hashing.md5()"); /** * Returns a hash function implementing the SHA-1 algorithm (160 hash bits) by delegating to the * SHA-1 {@link MessageDigest}. */ public static HashFunction sha1() { return SHA_1; } private static final HashFunction SHA_1 = new MessageDigestHashFunction("SHA-1", "Hashing.sha1()"); /** * Returns a hash function implementing the SHA-256 algorithm (256 hash bits) by delegating to * the SHA-256 {@link MessageDigest}. */ public static HashFunction sha256() { return SHA_256; } private static final HashFunction SHA_256 = new MessageDigestHashFunction("SHA-256", "Hashing.sha256()"); /** * Returns a hash function implementing the SHA-512 algorithm (512 hash bits) by delegating to the * SHA-512 {@link MessageDigest}. */ public static HashFunction sha512() { return SHA_512; } private static final HashFunction SHA_512 = new MessageDigestHashFunction("SHA-512", "Hashing.sha512()"); /** * Returns a hash function implementing the CRC-32 checksum algorithm (32 hash bits) by delegating * to the {@link CRC32} {@link Checksum}. * *
To get the {@code long} value equivalent to {@link Checksum#getValue()} for a * {@code HashCode} produced by this function, use {@link HashCode#padToLong()}. * * @since 14.0 */ public static HashFunction crc32() { return CRC_32; } private static final HashFunction CRC_32 = checksumHashFunction(ChecksumType.CRC_32, "Hashing.crc32()"); /** * Returns a hash function implementing the Adler-32 checksum algorithm (32 hash bits) by * delegating to the {@link Adler32} {@link Checksum}. * *
To get the {@code long} value equivalent to {@link Checksum#getValue()} for a
* {@code HashCode} produced by this function, use {@link HashCode#padToLong()}.
*
* @since 14.0
*/
public static HashFunction adler32() {
return ADLER_32;
}
private static final HashFunction ADLER_32 =
checksumHashFunction(ChecksumType.ADLER_32, "Hashing.adler32()");
private static HashFunction checksumHashFunction(ChecksumType type, String toString) {
return new ChecksumHashFunction(type, type.bits, toString);
}
enum ChecksumType implements Supplier See the wikipedia
* article on consistent hashing for more information.
*
* If you might want to have weights for the buckets in the future, take a look at
* {@code weightedConsistentHash}.
*/
public static int consistentHash(HashCode hashCode, int buckets) {
return consistentHash(hashCode.padToLong(), buckets);
}
/**
* Assigns to {@code input} a "bucket" in the range {@code [0, buckets)}, in a uniform
* manner that minimizes the need for remapping as {@code buckets} grows. That is,
* {@code consistentHash(h, n)} equals:
*
* See the wikipedia
* article on consistent hashing for more information.
*
* If you might want to have weights for the buckets in the future, take a look at
* {@code weightedConsistentHash}.
*/
public static int consistentHash(long input, int buckets) {
checkArgument(buckets > 0, "buckets must be positive: %s", buckets);
LinearCongruentialGenerator generator = new LinearCongruentialGenerator(input);
int candidate = 0;
int next;
// Jump from bucket to bucket until we go out of range
while (true) {
next = (int) ((candidate + 1) / generator.nextDouble());
if (next >= 0 && next < buckets) {
candidate = next;
} else {
return candidate;
}
}
}
/**
* Returns a hash code, having the same bit length as each of the input hash codes,
* that combines the information of these hash codes in an ordered fashion. That
* is, whenever two equal hash codes are produced by two calls to this method, it
* is as likely as possible that each was computed from the same
* input hash codes in the same order.
*
* @throws IllegalArgumentException if {@code hashCodes} is empty, or the hash codes
* do not all have the same bit length
*/
public static HashCode combineOrdered(Iterable
*
*
*
*
*
*