Package com.google.common.hash

Class FarmHashFingerprint64

java.lang.Object

com.google.common.hash.AbstractHashFunction

com.google.common.hash.AbstractNonStreamingHashFunction

com.google.common.hash.FarmHashFingerprint64

All Implemented Interfaces:

HashFunction

final class FarmHashFingerprint64
extends AbstractNonStreamingHashFunction

Implementation of FarmHash Fingerprint64, an open-source fingerprinting algorithm for strings.

Its speed is comparable to CityHash64, and its quality of hashing is at least as good.

Note to maintainers: This implementation relies on signed arithmetic being bit-wise equivalent to unsigned arithmetic in all cases except:

• comparisons (signed values can be negative)
• division (avoided here)
• shifting (right shift must be unsigned)

Field Summary

Fields

Modifier and Type	Field	Description
(package private) static HashFunction	FARMHASH_FINGERPRINT_64
private static long	K0
private static long	K1
private static long	K2

Constructor Summary

Constructors

Constructor	Description
FarmHashFingerprint64()

Method Summary

Modifier and Type	Method	Description
int	bits()	Returns the number of bits (a multiple of 32) that each hash code produced by this hash function has.
(package private) static long	fingerprint(byte[] bytes, int offset, int length)
HashCode	hashBytes(byte[] input, int off, int len)	Shortcut for newHasher().putBytes(input, off, len).hash().
private static long	hashLength0to16(byte[] bytes, int offset, int length)
private static long	hashLength16(long u, long v, long mul)
private static long	hashLength17to32(byte[] bytes, int offset, int length)
private static long	hashLength33To64(byte[] bytes, int offset, int length)
private static long	hashLength65Plus(byte[] bytes, int offset, int length)
private static long	shiftMix(long val)
java.lang.String	toString()
private static void	weakHashLength32WithSeeds(byte[] bytes, int offset, long seedA, long seedB, long[] output)	Computes intermediate hash of 32 bytes of byte array from the given offset.

Methods inherited from class com.google.common.hash.AbstractNonStreamingHashFunction

hashBytes, hashInt, hashLong, hashString, hashUnencodedChars, newHasher, newHasher

Methods inherited from class com.google.common.hash.AbstractHashFunction

hashBytes, hashObject

Methods inherited from class java.lang.Object

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

Field Detail

FARMHASH_FINGERPRINT_64

static final HashFunction FARMHASH_FINGERPRINT_64

K0

private static final long K0

See Also:

Constant Field Values

K1

private static final long K1

See Also:

Constant Field Values

K2

private static final long K2

See Also:

Constant Field Values

Constructor Detail

FarmHashFingerprint64

FarmHashFingerprint64()

Method Detail

hashBytes

public HashCode hashBytes(byte[] input,
                          int off,
                          int len)

Description copied from interface: HashFunction

Shortcut for newHasher().putBytes(input, off, len).hash(). The implementation might perform better than its longhand equivalent, but should not perform worse.

Specified by:

hashBytes in interface HashFunction

Specified by:

hashBytes in class AbstractNonStreamingHashFunction

bits

public int bits()

Description copied from interface: HashFunction

Returns the number of bits (a multiple of 32) that each hash code produced by this hash function has.

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

fingerprint

static long fingerprint(byte[] bytes,
                        int offset,
                        int length)

shiftMix

private static long shiftMix(long val)

hashLength16

private static long hashLength16(long u,
                                 long v,
                                 long mul)

weakHashLength32WithSeeds

private static void weakHashLength32WithSeeds(byte[] bytes,
                                              int offset,
                                              long seedA,
                                              long seedB,
                                              long[] output)

Computes intermediate hash of 32 bytes of byte array from the given offset. Results are returned in the output array because when we last measured, this was 12% faster than allocating new arrays every time.

hashLength0to16

private static long hashLength0to16(byte[] bytes,
                                    int offset,
                                    int length)

hashLength17to32

private static long hashLength17to32(byte[] bytes,
                                     int offset,
                                     int length)

hashLength33To64

private static long hashLength33To64(byte[] bytes,
                                     int offset,
                                     int length)

hashLength65Plus

private static long hashLength65Plus(byte[] bytes,
                                     int offset,
                                     int length)