com.landawn.abacus.guava.hash

Class Hashing

java.lang.Object

com.landawn.abacus.guava.hash.Hashing

public final class Hashing
extends Object

Note: It's copied from Google Guava under Apache License 2.0 and modified. Static methods to obtain HashFunction instances, and other static hashing-related utilities.

A comparison of the various hash functions can be found here.

Since:

11.0

Author:

Kevin Bourrillion, Dimitris Andreou, Kurt Alfred Kluever

Method Summary

Modifier and Type	Method and Description
static HashFunction	adler32() Returns a hash function implementing the Adler-32 checksum algorithm (32 hash bits) by delegating to the Adler32 Checksum.
static com.google.common.hash.HashCode	combineOrdered(com.google.common.hash.HashCode first, com.google.common.hash.HashCode second)
static com.google.common.hash.HashCode	combineOrdered(com.google.common.hash.HashCode first, com.google.common.hash.HashCode second, com.google.common.hash.HashCode third)
static com.google.common.hash.HashCode	combineOrdered(Iterable<com.google.common.hash.HashCode> hashCodes) 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.
static com.google.common.hash.HashCode	combineUnordered(com.google.common.hash.HashCode first, com.google.common.hash.HashCode second)
static com.google.common.hash.HashCode	combineUnordered(com.google.common.hash.HashCode first, com.google.common.hash.HashCode second, com.google.common.hash.HashCode third)
static com.google.common.hash.HashCode	combineUnordered(Iterable<com.google.common.hash.HashCode> hashCodes) 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 unordered fashion.
static HashFunction	concatenating(HashFunction first, HashFunction second)
static HashFunction	concatenating(HashFunction first, HashFunction second, HashFunction third)
static HashFunction	concatenating(Iterable<HashFunction> hashFunctions) Returns a hash function which computes its hash code by concatenating the hash codes of the underlying hash functions together.
static int	consistentHash(com.google.common.hash.HashCode hashCode, int buckets) Assigns to hashCode a "bucket" in the range [0, buckets), in a uniform manner that minimizes the need for remapping as buckets grows.
static int	consistentHash(long input, int buckets) Assigns to input a "bucket" in the range [0, buckets), in a uniform manner that minimizes the need for remapping as buckets grows.
static HashFunction	crc32() Returns a hash function implementing the CRC-32 checksum algorithm (32 hash bits) by delegating to the CRC32 Checksum.
static HashFunction	crc32c() Returns a hash function implementing the CRC32C checksum algorithm (32 hash bits) as described by RFC 3720, Section 12.1.
static HashFunction	farmHashFingerprint64() Returns a hash function implementing FarmHash's Fingerprint64, an open-source algorithm.
static HashFunction	goodFastHash(int minimumBits) Returns a general-purpose, temporary-use, non-cryptographic hash function.
static HashFunction	hmacMd5(byte[] key) Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the MD5 (128 hash bits) hash function and a SecretSpecKey created from the given byte array and the MD5 algorithm.
static HashFunction	hmacMd5(Key key) Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the MD5 (128 hash bits) hash function and the given secret key.
static HashFunction	hmacSha1(byte[] key) Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-1 (160 hash bits) hash function and a SecretSpecKey created from the given byte array and the SHA-1 algorithm.
static HashFunction	hmacSha1(Key key) Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-1 (160 hash bits) hash function and the given secret key.
static HashFunction	hmacSha256(byte[] key) Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-256 (256 hash bits) hash function and a SecretSpecKey created from the given byte array and the SHA-256 algorithm.
static HashFunction	hmacSha256(Key key) Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-256 (256 hash bits) hash function and the given secret key.
static HashFunction	hmacSha512(byte[] key) Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-512 (512 hash bits) hash function and a SecretSpecKey created from the given byte array and the SHA-512 algorithm.
static HashFunction	hmacSha512(Key key) Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-512 (512 hash bits) hash function and the given secret key.
static HashFunction	md5() Deprecated. If you must interoperate with a system that requires MD5, then use this method, despite its deprecation. But if you can choose your hash function, avoid MD5, which is neither fast nor secure. As of January 2017, we suggest: For security: sha256() or a higher-level API. For speed: goodFastHash(int), though see its docs for caveats.
static HashFunction	murmur3_128() Returns a hash function implementing the 128-bit murmur3 algorithm, x64 variant (little-endian variant), using a seed value of zero.
static HashFunction	murmur3_128(int seed) Returns a hash function implementing the 128-bit murmur3 algorithm, x64 variant (little-endian variant), using the given seed value.
static HashFunction	murmur3_32() Returns a hash function implementing the 32-bit murmur3 algorithm, x86 variant (little-endian variant), using a seed value of zero.
static HashFunction	murmur3_32(int seed) Returns a hash function implementing the 32-bit murmur3 algorithm, x86 variant (little-endian variant), using the given seed value.
static HashFunction	sha1() Deprecated. If you must interoperate with a system that requires SHA-1, then use this method, despite its deprecation. But if you can choose your hash function, avoid SHA-1, which is neither fast nor secure. As of January 2017, we suggest: For security: sha256() or a higher-level API. For speed: goodFastHash(int), though see its docs for caveats.
static HashFunction	sha256() Returns a hash function implementing the SHA-256 algorithm (256 hash bits) by delegating to the SHA-256 MessageDigest.
static HashFunction	sha384() Returns a hash function implementing the SHA-384 algorithm (384 hash bits) by delegating to the SHA-384 MessageDigest.
static HashFunction	sha512() Returns a hash function implementing the SHA-512 algorithm (512 hash bits) by delegating to the SHA-512 MessageDigest.
static HashFunction	sipHash24() Returns a hash function implementing the 64-bit SipHash-2-4 algorithm using a seed value of k = 00 01 02 ....
static HashFunction	sipHash24(long k0, long k1) Returns a hash function implementing the 64-bit SipHash-2-4 algorithm using the given seed.

Methods inherited from class java.lang.Object

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

Method Detail

goodFastHash

public static HashFunction goodFastHash(int minimumBits)

Returns a general-purpose, temporary-use, non-cryptographic hash function. The algorithm the returned function implements is unspecified and subject to change without notice.

Warning: a new random seed for these functions is chosen each time the Hashing class is loaded. Do not use this method if hash codes may escape the current process in any way, for example being sent over RPC, or saved to disk.

Repeated calls to this method on the same loaded Hashing class, using the same value for minimumBits, will return identically-behaving HashFunction instances.

Parameters:

minimumBits - a positive integer (can be arbitrarily large)

Returns:

a hash function, described above, that produces hash codes of length minimumBits or greater

murmur3_32

public static HashFunction murmur3_32(int seed)

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).

Parameters:

seed -

Returns:

murmur3_32

public static HashFunction murmur3_32()

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).

Returns:

murmur3_128

public static HashFunction murmur3_128(int seed)

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).

Parameters:

seed -

Returns:

murmur3_128

public static HashFunction murmur3_128()

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).

Returns:

sipHash24

public static HashFunction sipHash24()

Returns a hash function implementing the 64-bit SipHash-2-4 algorithm using a seed value of k = 00 01 02 ....

Returns:

Since:

15.0

sipHash24

public static HashFunction sipHash24(long k0,
                                     long k1)

Returns a hash function implementing the 64-bit SipHash-2-4 algorithm using the given seed.

Parameters:

k0 -

k1 -

Returns:

Since:

15.0

md5

@Deprecated
public static HashFunction md5()

Deprecated. If you must interoperate with a system that requires MD5, then use this method, despite its deprecation. But if you can choose your hash function, avoid MD5, which is neither fast nor secure. As of January 2017, we suggest:

• For security: sha256() or a higher-level API.
• For speed: goodFastHash(int), though see its docs for caveats.

Returns a hash function implementing the MD5 hash algorithm (128 hash bits).

sha1

@Deprecated
public static HashFunction sha1()

Deprecated. If you must interoperate with a system that requires SHA-1, then use this method, despite its deprecation. But if you can choose your hash function, avoid SHA-1, which is neither fast nor secure. As of January 2017, we suggest:

• For security: sha256() or a higher-level API.
• For speed: goodFastHash(int), though see its docs for caveats.

Returns a hash function implementing the SHA-1 algorithm (160 hash bits).

sha256

public static HashFunction sha256()

Returns a hash function implementing the SHA-256 algorithm (256 hash bits) by delegating to the SHA-256 MessageDigest.

Returns:

sha384

public static HashFunction sha384()

Returns a hash function implementing the SHA-384 algorithm (384 hash bits) by delegating to the SHA-384 MessageDigest.

Returns:

Since:

19.0

sha512

public static HashFunction sha512()

Returns a hash function implementing the SHA-512 algorithm (512 hash bits) by delegating to the SHA-512 MessageDigest.

Returns:

hmacMd5

public static HashFunction hmacMd5(Key key)

Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the MD5 (128 hash bits) hash function and the given secret key.

Parameters:

key - the secret key

Returns:

Throws:

IllegalArgumentException - if the given key is inappropriate for initializing this MAC

Since:

20.0

hmacMd5

public static HashFunction hmacMd5(byte[] key)

Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the MD5 (128 hash bits) hash function and a SecretSpecKey created from the given byte array and the MD5 algorithm.

Parameters:

key - the key material of the secret key

Returns:

Since:

20.0

hmacSha1

public static HashFunction hmacSha1(Key key)

Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-1 (160 hash bits) hash function and the given secret key.

Parameters:

key - the secret key

Returns:

Throws:

IllegalArgumentException - if the given key is inappropriate for initializing this MAC

Since:

20.0

hmacSha1

public static HashFunction hmacSha1(byte[] key)

Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-1 (160 hash bits) hash function and a SecretSpecKey created from the given byte array and the SHA-1 algorithm.

Parameters:

key - the key material of the secret key

Returns:

Since:

20.0

hmacSha256

public static HashFunction hmacSha256(Key key)

Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-256 (256 hash bits) hash function and the given secret key.

Parameters:

key - the secret key

Returns:

Throws:

IllegalArgumentException - if the given key is inappropriate for initializing this MAC

Since:

20.0

hmacSha256

public static HashFunction hmacSha256(byte[] key)

Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-256 (256 hash bits) hash function and a SecretSpecKey created from the given byte array and the SHA-256 algorithm.

Parameters:

key - the key material of the secret key

Returns:

Since:

20.0

hmacSha512

public static HashFunction hmacSha512(Key key)

Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-512 (512 hash bits) hash function and the given secret key.

Parameters:

key - the secret key

Returns:

Throws:

IllegalArgumentException - if the given key is inappropriate for initializing this MAC

Since:

20.0

hmacSha512

public static HashFunction hmacSha512(byte[] key)

Returns a hash function implementing the Message Authentication Code (MAC) algorithm, using the SHA-512 (512 hash bits) hash function and a SecretSpecKey created from the given byte array and the SHA-512 algorithm.

Parameters:

key - the key material of the secret key

Returns:

Since:

20.0

crc32c

public static HashFunction crc32c()

Returns a hash function implementing the CRC32C checksum algorithm (32 hash bits) as described by RFC 3720, Section 12.1.

Returns:

Since:

18.0

crc32

public static HashFunction crc32()

Returns a hash function implementing the CRC-32 checksum algorithm (32 hash bits) by delegating to the CRC32 Checksum.

To get the long value equivalent to Checksum.getValue() for a HashCode produced by this function, use HashCode.padToLong().

Returns:

Since:

14.0

adler32

public static HashFunction adler32()

Returns a hash function implementing the Adler-32 checksum algorithm (32 hash bits) by delegating to the Adler32 Checksum.

To get the long value equivalent to Checksum.getValue() for a HashCode produced by this function, use HashCode.padToLong().

Returns:

Since:

14.0

farmHashFingerprint64

public static HashFunction farmHashFingerprint64()

Returns a hash function implementing FarmHash's Fingerprint64, an open-source algorithm.

This is designed for generating persistent fingerprints of strings. It isn't cryptographically secure, but it produces a high-quality hash with fewer collisions than some alternatives we've used in the past. FarmHashFingerprints generated using this are byte-wise identical to those created using the C++ version, but note that this uses unsigned integers (see UnsignedInts). Comparisons between the two should take this into account.

Returns:

Since:

20.0

concatenating

public static HashFunction concatenating(HashFunction first,
                                         HashFunction second)

Parameters:

first -

second -

Returns:

concatenating

public static HashFunction concatenating(HashFunction first,
                                         HashFunction second,
                                         HashFunction third)

Parameters:

first -

second -

third -

Returns:

concatenating

public static HashFunction concatenating(Iterable<HashFunction> hashFunctions)

Returns a hash function which computes its hash code by concatenating the hash codes of the underlying hash functions together. This can be useful if you need to generate hash codes of a specific length.

For example, if you need 1024-bit hash codes, you could join two sha512() hash functions together: Hashing.concatenating(Hashing.sha512(), Hashing.sha512()).

Parameters:

hashFunctions -

Returns:

Since:

19.0

combineOrdered

public static com.google.common.hash.HashCode combineOrdered(com.google.common.hash.HashCode first,
                                                             com.google.common.hash.HashCode second)

Parameters:

first -

second -

Returns:

combineOrdered

public static com.google.common.hash.HashCode combineOrdered(com.google.common.hash.HashCode first,
                                                             com.google.common.hash.HashCode second,
                                                             com.google.common.hash.HashCode third)

Parameters:

first -

second -

third -

Returns:

combineOrdered

public static com.google.common.hash.HashCode combineOrdered(Iterable<com.google.common.hash.HashCode> hashCodes)

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.

Parameters:

hashCodes -

Returns:

Throws:

IllegalArgumentException - if hashCodes is empty, or the hash codes do not all have the same bit length

combineUnordered

public static com.google.common.hash.HashCode combineUnordered(com.google.common.hash.HashCode first,
                                                               com.google.common.hash.HashCode second)

Parameters:

first -

second -

Returns:

combineUnordered

public static com.google.common.hash.HashCode combineUnordered(com.google.common.hash.HashCode first,
                                                               com.google.common.hash.HashCode second,
                                                               com.google.common.hash.HashCode third)

Parameters:

first -

second -

third -

Returns:

combineUnordered

public static com.google.common.hash.HashCode combineUnordered(Iterable<com.google.common.hash.HashCode> hashCodes)

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 unordered 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 some order.

Parameters:

hashCodes -

Returns:

Throws:

IllegalArgumentException - if hashCodes is empty, or the hash codes do not all have the same bit length

consistentHash

public static int consistentHash(com.google.common.hash.HashCode hashCode,
                                 int buckets)

Assigns to hashCode a "bucket" in the range [0, buckets), in a uniform manner that minimizes the need for remapping as buckets grows. That is, consistentHash(h, n) equals:

• n - 1, with approximate probability 1/n
• consistentHash(h, n - 1), otherwise (probability 1 - 1/n)

This method is suitable for the common use case of dividing work among buckets that meet the following conditions:

• You want to assign the same fraction of inputs to each bucket.
• When you reduce the number of buckets, you can accept that the most recently added buckets will be removed first. More concretely, if you are dividing traffic among tasks, you can decrease the number of tasks from 15 and 10, killing off the final 5 tasks, and consistentHash will handle it. If, however, you are dividing traffic among servers alpha, bravo, and charlie and you occasionally need to take each of the servers offline, consistentHash will be a poor fit: It provides no way for you to specify which of the three buckets is disappearing. Thus, if your buckets change from [alpha, bravo, charlie] to [bravo, charlie], it will assign all the old alpha traffic to bravo and all the old bravo traffic to charlie, rather than letting bravo keep its traffic.

See the Wikipedia article on consistent hashing for more information.

Parameters:

hashCode -

buckets -

Returns:

consistentHash

public static int consistentHash(long input,
                                 int buckets)

Assigns to input a "bucket" in the range [0, buckets), in a uniform manner that minimizes the need for remapping as buckets grows. That is, consistentHash(h, n) equals:

• n - 1, with approximate probability 1/n
• consistentHash(h, n - 1), otherwise (probability 1 - 1/n)

This method is suitable for the common use case of dividing work among buckets that meet the following conditions:

• You want to assign the same fraction of inputs to each bucket.
• When you reduce the number of buckets, you can accept that the most recently added buckets will be removed first. More concretely, if you are dividing traffic among tasks, you can decrease the number of tasks from 15 and 10, killing off the final 5 tasks, and consistentHash will handle it. If, however, you are dividing traffic among servers alpha, bravo, and charlie and you occasionally need to take each of the servers offline, consistentHash will be a poor fit: It provides no way for you to specify which of the three buckets is disappearing. Thus, if your buckets change from [alpha, bravo, charlie] to [bravo, charlie], it will assign all the old alpha traffic to bravo and all the old bravo traffic to charlie, rather than letting bravo keep its traffic.

See the Wikipedia article on consistent hashing for more information.

Parameters:

input -

buckets -

Returns: