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.

NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

Field Summary

static byte[]	nlzTable table of number of leading zeros in a byte
static byte[]	ntzTable table of number of trailing zeros in a byte

Method Summary

static boolean	isPowerOfTwo(int v) returns true if v is a power of two or zero
static boolean	isPowerOfTwo(long v) returns true if v is a power of two or zero
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 int	nlz(long x) Returns the number of leading zero bits.
static int	ntz(int val) Returns number of trailing zeros in a 32 bit int value.
static int	ntz(long val) Returns number of trailing zeros in a 64 bit long value.
static int	ntz2(long x) returns 0 based index of first set bit (only works for x!=0) This is an alternate implementation of ntz()
static int	ntz3(long x) returns 0 based index of first set bit This is an alternate implementation of ntz()
static long	pop_andnot(long[] A, long[] B, int wordOffset, int numWords) Returns the popcount or cardinality of A & ~B Neither array is modified.
static long	pop_array(long[] A, int wordOffset, int numWords) Returns the number of set bits in an array of longs.
static long	pop_intersect(long[] A, long[] B, int wordOffset, int numWords) Returns the popcount or cardinality of the two sets after an intersection.
static long	pop_union(long[] A, long[] B, int wordOffset, int numWords) Returns the popcount or cardinality of the union of two sets.
static long	pop_xor(long[] A, long[] B, int wordOffset, int numWords)
static int	pop(long x) Returns the number of bits set in the long

Methods inherited from class java.lang.Object

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

Field Detail

ntzTable

public static final byte[] ntzTable

table of number of trailing zeros in a byte

nlzTable

public static final byte[] nlzTable

table of number of leading zeros in a byte

Method Detail

pop

public static int pop(long x)

Returns the number of bits set in the long

pop_array

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

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

pop_intersect

public static long pop_intersect(long[] A,
                                 long[] B,
                                 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[] A,
                             long[] B,
                             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[] A,
                              long[] B,
                              int wordOffset,
                              int numWords)

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

pop_xor

public static long pop_xor(long[] A,
                           long[] B,
                           int wordOffset,
                           int numWords)

ntz

public static int ntz(long val)

Returns number of trailing zeros in a 64 bit long value.

ntz

public static int ntz(int val)

Returns number of trailing zeros in a 32 bit int value.

ntz2

public static int ntz2(long x)

returns 0 based index of first set bit (only works for x!=0)
This is an alternate implementation of ntz()

ntz3

public static int ntz3(long x)

returns 0 based index of first set bit
This is an alternate implementation of ntz()

nlz

public static int nlz(long x)

Returns the number of leading zero bits.

isPowerOfTwo

public static boolean isPowerOfTwo(int v)

returns true if v is a power of two or zero

isPowerOfTwo

public static boolean isPowerOfTwo(long v)

returns true if v is a power of two or zero

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