Class HashCommon

Method Summary
Modifier and TypeMethodDescriptionstatic int
arraySize
(int expected, float f) Returns the least power of two smaller than or equal to 2^{30} and larger than or equal toMath.ceil(expected / f)
.static long
bigArraySize
(long expected, float f) Returns the least power of two larger than or equal toMath.ceil(expected / f)
.static int
double2int
(double d) Returns the hash code that would be returned byDouble.hashCode()
.static int
float2int
(float f) Returns the hash code that would be returned byFloat.hashCode()
.static int
invMix
(int x) The inverse ofmix(int)
.static long
invMix
(long x) The inverse ofmix(long)
.static int
long2int
(long l) Returns the hash code that would be returned byLong.hashCode()
.static int
maxFill
(int n, float f) Returns the maximum number of entries that can be filled before rehashing.static long
maxFill
(long n, float f) Returns the maximum number of entries that can be filled before rehashing.static int
mix
(int x) Quickly mixes the bits of an integer.static long
mix
(long x) Quickly mixes the bits of a long integer.static int
murmurHash3
(int x) Avalanches the bits of an integer by applying the finalisation step of MurmurHash3.static long
murmurHash3
(long x) Avalanches the bits of a long integer by applying the finalisation step of MurmurHash3.static int
nextPowerOfTwo
(int x) Returns the least power of two greater than or equal to the specified value.static long
nextPowerOfTwo
(long x) Returns the least power of two greater than or equal to the specified value.

Method Details

murmurHash3
public static int murmurHash3(int x) Avalanches the bits of an integer by applying the finalisation step of MurmurHash3.This method implements the finalisation step of Austin Appleby's MurmurHash3. Its purpose is to avalanche the bits of the argument to within 0.25% bias.
 Parameters:
x
 an integer. Returns:
 a hash value with good avalanching properties.

murmurHash3
public static long murmurHash3(long x) Avalanches the bits of a long integer by applying the finalisation step of MurmurHash3.This method implements the finalisation step of Austin Appleby's MurmurHash3. Its purpose is to avalanche the bits of the argument to within 0.25% bias.
 Parameters:
x
 a long integer. Returns:
 a hash value with good avalanching properties.

mix
public static int mix(int x) Quickly mixes the bits of an integer.This method mixes the bits of the argument by multiplying by the golden ratio and xorshifting the result. It is borrowed from Koloboke, and it has slightly worse behaviour than
murmurHash3(int)
(in openaddressing hash tables the average number of probes is slightly larger), but it's much faster. Parameters:
x
 an integer. Returns:
 a hash value obtained by mixing the bits of
x
.  See Also:

invMix
public static int invMix(int x) The inverse ofmix(int)
. This method is mainly useful to create unit tests. Parameters:
x
 an integer. Returns:
 a value that passed through
mix(int)
would givex
.

mix
public static long mix(long x) Quickly mixes the bits of a long integer.This method mixes the bits of the argument by multiplying by the golden ratio and xorshifting twice the result. It is borrowed from Koloboke, and it has slightly worse behaviour than
murmurHash3(long)
(in openaddressing hash tables the average number of probes is slightly larger), but it's much faster. Parameters:
x
 a long integer. Returns:
 a hash value obtained by mixing the bits of
x
.

invMix
public static long invMix(long x) The inverse ofmix(long)
. This method is mainly useful to create unit tests. Parameters:
x
 a long integer. Returns:
 a value that passed through
mix(long)
would givex
.

float2int
public static int float2int(float f) Returns the hash code that would be returned byFloat.hashCode()
. Parameters:
f
 a float. Returns:
 the same code as
new Float(f).hashCode()
.

double2int
public static int double2int(double d) Returns the hash code that would be returned byDouble.hashCode()
. Parameters:
d
 a double. Returns:
 the same code as
new Double(f).hashCode()
.

long2int
public static int long2int(long l) Returns the hash code that would be returned byLong.hashCode()
. Parameters:
l
 a long. Returns:
 the same code as
new Long(f).hashCode()
.

nextPowerOfTwo
public static int nextPowerOfTwo(int x) Returns the least power of two greater than or equal to the specified value.Note that this function will return 1 when the argument is 0.
 Parameters:
x
 an integer smaller than or equal to 2^{30}. Returns:
 the least power of two greater than or equal to the specified value.

nextPowerOfTwo
public static long nextPowerOfTwo(long x) Returns the least power of two greater than or equal to the specified value.Note that this function will return 1 when the argument is 0.
 Parameters:
x
 a long integer smaller than or equal to 2^{62}. Returns:
 the least power of two greater than or equal to the specified value.

maxFill
public static int maxFill(int n, float f) Returns the maximum number of entries that can be filled before rehashing. Parameters:
n
 the size of the backing array.f
 the load factor. Returns:
 the maximum number of entries before rehashing.

maxFill
public static long maxFill(long n, float f) Returns the maximum number of entries that can be filled before rehashing. Parameters:
n
 the size of the backing array.f
 the load factor. Returns:
 the maximum number of entries before rehashing.

arraySize
public static int arraySize(int expected, float f) Returns the least power of two smaller than or equal to 2^{30} and larger than or equal toMath.ceil(expected / f)
. Parameters:
expected
 the expected number of elements in a hash table.f
 the load factor. Returns:
 the minimum possible size for a backing array.
 Throws:
IllegalArgumentException
 if the necessary size is larger than 2^{30}.

bigArraySize
public static long bigArraySize(long expected, float f) Returns the least power of two larger than or equal toMath.ceil(expected / f)
. Parameters:
expected
 the expected number of elements in a hash table.f
 the load factor. Returns:
 the minimum possible size for a backing big array.
