org.apache.arrow.memory.util.hash

Class MurmurHasher

java.lang.Object

org.apache.arrow.memory.util.hash.MurmurHasher

All Implemented Interfaces:

ArrowBufHasher

public class MurmurHasher
extends Object
implements ArrowBufHasher

Implementation of the Murmur hashing algorithm. Details of the algorithm can be found in https://en.wikipedia.org/wiki/MurmurHash

Murmur hashing is computationally expensive, as it involves several integer multiplications. However, the produced hash codes have good quality in the sense that they are uniformly distributed in the universe.

Therefore, this algorithm is suitable for scenarios where uniform hashing is desired (e.g. in an open addressing hash table/hash set).

Constructor Summary

Constructors

Constructor and Description
MurmurHasher() Creates a default Murmur hasher, with seed 0.
MurmurHasher(int seed) Creates a Murmur hasher.

Method Summary

Modifier and Type	Method and Description
static int	combineHashCode(int currentHashCode, int intValue) Combine the current hash code and a new int value to calculate a new hash code.
boolean	equals(Object o)
static int	finalizeHashCode(int hashCode, int length) Finalizing the hash code.
int	hashCode()
int	hashCode(ArrowBuf buf, int offset, int length) Calculates the hash code for a memory region.
static int	hashCode(ArrowBuf buf, int offset, int length, int seed) Calculates the hash code for a memory region.
int	hashCode(long address, int length) Calculates the hash code for a memory region.
static int	hashCode(long address, int length, int seed) Calculates the hash code for a memory region.

Methods inherited from class java.lang.Object

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

Constructor Detail

MurmurHasher

public MurmurHasher()

Creates a default Murmur hasher, with seed 0.

MurmurHasher

public MurmurHasher(int seed)

Creates a Murmur hasher.

Parameters:

seed - the seed for the hasher.

Method Detail

hashCode

public int hashCode(long address,
                    int length)

Description copied from interface: ArrowBufHasher

Calculates the hash code for a memory region.

Specified by:

hashCode in interface ArrowBufHasher

Parameters:

address - start address of the memory region.

length - length of the memory region.

Returns:

the hash code.

hashCode

public int hashCode(ArrowBuf buf,
                    int offset,
                    int length)

Description copied from interface: ArrowBufHasher

Calculates the hash code for a memory region.

Specified by:

hashCode in interface ArrowBufHasher

Parameters:

buf - the buffer for the memory region.

offset - offset within the buffer for the memory region.

length - length of the memory region.

Returns:

the hash code.

hashCode

public static int hashCode(ArrowBuf buf,
                           int offset,
                           int length,
                           int seed)

Calculates the hash code for a memory region.

Parameters:

buf - the buffer for the memory region.

offset - offset within the buffer for the memory region.

length - length of the memory region.

seed - the seed.

Returns:

the hash code.

hashCode

public static int hashCode(long address,
                           int length,
                           int seed)

Calculates the hash code for a memory region.

Parameters:

address - start address of the memory region.

length - length of the memory region.

seed - the seed.

Returns:

the hash code.

combineHashCode

public static int combineHashCode(int currentHashCode,
                                  int intValue)

Combine the current hash code and a new int value to calculate a new hash code.

Parameters:

currentHashCode - the current hash code.

intValue - the new int value.

Returns:

the new hah code.

finalizeHashCode

public static int finalizeHashCode(int hashCode,
                                   int length)

Finalizing the hash code.

Parameters:

hashCode - the current hash code.

length - the length of the memory region.

Returns:

the finalized hash code.

equals

public boolean equals(Object o)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object