org.apache.lucene.util

Class BroadWord

java.lang.Object

org.apache.lucene.util.BroadWord

public final class BroadWord
extends Object

Methods and constants inspired by the article "Broadword Implementation of Rank/Select Queries" by Sebastiano Vigna, January 30, 2012:

• algorithm 1: bitCount(long), count of set bits in a long
• algorithm 2: select(long, int), selection of a set bit in a long,
• bytewise signed smaller <₈ operator: smallerUpTo7_8(long,long).
• shortwise signed smaller <₁₆ operator: smallerUpto15_16(long,long).
• some of the Lk and Hk constants that are used by the above: L8 L8_L, H8 H8_L, L9 L9_L, L16 L16_Land H16 H8_L.

Field Summary

Fields

Modifier and Type	Field and Description
static long	H16_L
static long	H8_L Hk = Lk << (k-1) .
static long	L16_L
static long	L8_L Lk denotes the constant whose ones are in position 0, k, 2k, .
static long	L9_L

Method Summary

Modifier and Type	Method and Description
static long	notEquals0_8(long x) An unsigned bytewise not equals 0 operator.
static int	select(long x, int r) Select a 1-bit from a long.
static int	selectNaive(long x, int r) Naive implementation of select(long,int), using Long.numberOfTrailingZeros(long) repetitively.
static long	smalleru_8(long x, long y) An unsigned bytewise smaller <8 operator.
static long	smallerUpto15_16(long x, long y) A bytewise smaller <16 operator.
static long	smallerUpTo7_8(long x, long y) A signed bytewise smaller <8 operator, for operands 0L<= x, y <=0x7L.

Methods inherited from class java.lang.Object

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

Field Detail

L8_L

public static final long L8_L

Lk denotes the constant whose ones are in position 0, k, 2k, . . . These contain the low bit of each group of k bits. The suffix _L indicates the long implementation.

See Also:

Constant Field Values

L9_L

public static final long L9_L

See Also:

Constant Field Values

L16_L

public static final long L16_L

See Also:

Constant Field Values

H8_L

public static final long H8_L

Hk = Lk << (k-1) . These contain the high bit of each group of k bits. The suffix _L indicates the long implementation.

See Also:

Constant Field Values

H16_L

public static final long H16_L

See Also:

Constant Field Values

Method Detail

select

public static int select(long x,
                         int r)

Select a 1-bit from a long.

Returns:

The index of the r-th 1 bit in x, or if no such bit exists, 72.

smallerUpTo7_8

public static long smallerUpTo7_8(long x,
                                  long y)

A signed bytewise smaller <₈ operator, for operands 0L<= x, y <=0x7L. This uses the following numbers of basic long operations: 1 or, 2 and, 2 xor, 1 minus, 1 not.

Returns:

A long with bits set in the H8_L positions corresponding to each input signed byte pair that compares smaller.

smalleru_8

public static long smalleru_8(long x,
                              long y)

An unsigned bytewise smaller <₈ operator. This uses the following numbers of basic long operations: 3 or, 2 and, 2 xor, 1 minus, 1 not.

Returns:

A long with bits set in the H8_L positions corresponding to each input unsigned byte pair that compares smaller.

notEquals0_8

public static long notEquals0_8(long x)

An unsigned bytewise not equals 0 operator. This uses the following numbers of basic long operations: 2 or, 1 and, 1 minus.

Returns:

A long with bits set in the H8_L positions corresponding to each unsigned byte that does not equal 0.

smallerUpto15_16

public static long smallerUpto15_16(long x,
                                    long y)

A bytewise smaller <₁₆ operator. This uses the following numbers of basic long operations: 1 or, 2 and, 2 xor, 1 minus, 1 not.

Returns:

A long with bits set in the H16_L positions corresponding to each input signed short pair that compares smaller.

selectNaive

public static int selectNaive(long x,
                              int r)

Naive implementation of select(long,int), using Long.numberOfTrailingZeros(long) repetitively. Works relatively fast for low ranks.

Returns:

The index of the r-th 1 bit in x, or if no such bit exists, 72.