Package org.apache.lucene.util

Class BitUtil

java.lang.Object

org.apache.lucene.util.BitUtil

public final class BitUtil
extends Object

A variety of high efficiency bit twiddling routines.

Method Summary

Modifier and Type	Method	Description
static int	bitCount(byte b)	Return the number of bits sets in b.
static int	bitList(byte b)	Return the list of bits which are set in b encoded as followed: (i >>> (4 * n)) & 0x0F is the offset of the n-th set bit of the given byte plus one, or 0 if there are n or less bits set in the given byte.
static int	nextHighestPowerOfTwo(int v)	returns the next highest power of two, or the current value if it's already a power of two or zero
static long	nextHighestPowerOfTwo(long v)	returns the next highest power of two, or the current value if it's already a power of two or zero
static long	pop_andnot(long[] arr1, long[] arr2, int wordOffset, int numWords)	Returns the popcount or cardinality of A & ~B.
static long	pop_array(long[] arr, int wordOffset, int numWords)	Returns the number of set bits in an array of longs.
static long	pop_intersect(long[] arr1, long[] arr2, int wordOffset, int numWords)	Returns the popcount or cardinality of the two sets after an intersection.
static long	pop_union(long[] arr1, long[] arr2, int wordOffset, int numWords)	Returns the popcount or cardinality of the union of two sets.
static long	pop_xor(long[] arr1, long[] arr2, int wordOffset, int numWords)	Returns the popcount or cardinality of A ^ B Neither array is modified.

Methods inherited from class java.lang.Object

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

Method Detail

bitCount

public static int bitCount(byte b)

Return the number of bits sets in b.

bitList

public static int bitList(byte b)

Return the list of bits which are set in b encoded as followed: (i >>> (4 * n)) & 0x0F is the offset of the n-th set bit of the given byte plus one, or 0 if there are n or less bits set in the given byte. For example bitList(12) returns 0x43:

• 0x43 & 0x0F is 3, meaning the the first bit set is at offset 3-1 = 2,
• (0x43 >>> 4) & 0x0F is 4, meaning there is a second bit set at offset 4-1=3,
• (0x43 >>> 8) & 0x0F is 0, meaning there is no more bit set in this byte.

pop_array

public static long pop_array(long[] arr,
                             int wordOffset,
                             int numWords)

Returns the number of set bits in an array of longs.

pop_intersect

public static long pop_intersect(long[] arr1,
                                 long[] arr2,
                                 int wordOffset,
                                 int numWords)

Returns the popcount or cardinality of the two sets after an intersection. Neither array is modified.

pop_union

public static long pop_union(long[] arr1,
                             long[] arr2,
                             int wordOffset,
                             int numWords)

Returns the popcount or cardinality of the union of two sets. Neither array is modified.

pop_andnot

public static long pop_andnot(long[] arr1,
                              long[] arr2,
                              int wordOffset,
                              int numWords)

Returns the popcount or cardinality of A & ~B. Neither array is modified.

pop_xor

public static long pop_xor(long[] arr1,
                           long[] arr2,
                           int wordOffset,
                           int numWords)

Returns the popcount or cardinality of A ^ B Neither array is modified.

nextHighestPowerOfTwo

public static int nextHighestPowerOfTwo(int v)

returns the next highest power of two, or the current value if it's already a power of two or zero

nextHighestPowerOfTwo

public static long nextHighestPowerOfTwo(long v)

returns the next highest power of two, or the current value if it's already a power of two or zero