Package it.unimi.dsi.bits

Class LongArrayBitVector

java.lang.Object
java.util.AbstractCollection<Boolean>
it.unimi.dsi.fastutil.booleans.AbstractBooleanCollection
it.unimi.dsi.fastutil.booleans.AbstractBooleanBigList
it.unimi.dsi.bits.AbstractBitVector
it.unimi.dsi.bits.LongArrayBitVector
All Implemented Interfaces:
BitVector, BigList<Boolean>, BooleanBigList, BooleanCollection, BooleanIterable, BooleanStack, Size64, Stack<Boolean>, Serializable, Cloneable, Comparable<BigList<? extends Boolean>>, Iterable<Boolean>, Collection<Boolean>, RandomAccess
public class LongArrayBitVector extends AbstractBitVector implements Cloneable, Serializable
A bit vector implementation based on arrays of longs.

The main goal of this class is to be fast and flexible. It implements a lightweight, fast, open, optimized, reuse-oriented version of bit vectors. Instances of this class represent a bit vector using an array of longs that is enlarged as needed when new entries are created (using LongArrays.grow(long[], int, int)), but is never made smaller (even on a clear()). Use trim() for that purpose.

Besides usual methods for setting and getting bits, this class provides views that make it possible to access comfortably the bit vector in different ways: for instance, asLongBigList(int) provide access as a list of longs, whereas AbstractBitVector.asLongSet() provides access in setwise form.

When enlarging the underlying array (e.g., for append(long, int) operations or add operations on the big list view), or when invoking ensureCapacity(long), this class calls LongArrays.grow(long[], int, int), which could enlarge the array more than expected. On the contrary, length(long) (and the corresponding method in the big list view) sizes the underlying array in an exact manner.

Bit numbering follows the right-to-left convention: bit k (counted from the right) of word w is bit 64w + k of the overall bit vector.

If CHECKS is true at compile time, boundary checks for all bit operations will be compiled in. For maximum speed, you may want to recompile this class with CHECKS set to false. CHECKS is public, so you can check from your code whether you're being provided a version with checks or not. In any case, many checks happen when you enable assertions.

Warning: A few optional methods have still to be implemented (e.g., adding an element at an arbitrary position using the list view).

Warning: In some cases, you might want to cache locally the result of bits() to speed up computations on immutable bit vectors (this is what happens, for instance, in static ranking structures). This class, however, does its own serialization of the bit vector: as a result, all cached references to the result of bits() must be marked as transient and rebuilt at deserialization time, or you will end up saving the bits twice.

See Also:

  • Field Details

    • LOG2_BITS_PER_WORD

      public static final int LOG2_BITS_PER_WORD

    • BITS_PER_WORD

      @Deprecated public static final int BITS_PER_WORD
      Deprecated.
      Please use Long.SIZE.
      See Also:

    • WORD_MASK

      @Deprecated public static final int WORD_MASK
      Deprecated.
      Please use ~-Long.SIZE.
      See Also:

    • LAST_BIT

      public static final int LAST_BIT
      See Also:

    • ALL_ONES

      public static final long ALL_ONES
      See Also:

    • LAST_BIT_MASK

      public static final long LAST_BIT_MASK
      See Also:

    • CHECKS

      public static final boolean CHECKS
      Whether this class has been compiled with index checks or not.
      See Also:

    • length

      protected long length
      The number of bits in this vector.

    • bits

      protected transient long[] bits
      The backing array of this vector. Bit 0 of the first element contains bit 0 of the bit vector, bit 0 of the second element contains bit Long.SIZE of the bit vector and so on.

  • Constructor Details

    • LongArrayBitVector

      protected LongArrayBitVector(long capacity)

  • Method Details

    • words

      public static final int words(long size)
      Returns the number of words that are necessary to hold the given number of bits.
      Parameters:
      size - a number of bits.
      Returns:
      the number of words that are necessary to hold the given number of bits.

    • word

      public static final int word(long index)
      Returns the index of the word that holds a bit of specified index.
      Parameters:
      index - the index of a bit, or -1.
      Returns:
      the index of the word that holds the bit of given index, or -1 if index is -1.

    • sameWord

      public static final boolean sameWord(long index0, long index1)
      Returns true if the two bit indices point at the same word.
      Parameters:
      index0 - the index of a bit, or -1.
      index1 - the index of a bit, or -1.
      Returns:
      true if the two indices point at the same word.

    • bits

      public static final long bits(int word)
      Returns the number of bits in the given number of words.
      Parameters:
      word - a word position.
      Returns:
      Long.SIZE * word.

    • round

      public static final boolean round(long index)
      Returns true if the argument is a multiple of Long.SIZE.
      Parameters:
      index - the index of a bit, or -1.
      Returns:
      true if index is a multiple of Long.SIZE.

    • bit

      public static final int bit(long index)
      Returns the inside-word index of the bit that would hold the bit of specified index.

      Note that bit 0 is positioned in word 0, index 0, bit 1 in word 0, index 1, …, bit BITS_PER_WORD in word 0, index 0, bit Long.SIZE + 1 in word 1, index 1, and so on.

      Parameters:
      index - the index of a bit.
      Returns:
      the inside-word index of the bit that would hold the bit of specified index.

    • mask

      public static final long mask(long index)
      Returns a mask having a 1 exactly at the bit bit(index).
      Parameters:
      index - the index of a bit
      Returns:
      a mask having a 1 exactly at the bit bit(index).

    • getInstance

      public static LongArrayBitVector getInstance(long capacity)
      Creates a new empty bit vector of given capacity. The resulting vector will be able to contain capacity bits without reallocations of the backing array.

      Note that this constructor creates an empty bit vector. If you want a cleared bit vector of a specified size, please use the ofLength(long) factory method.

      Parameters:
      capacity - the capacity (in bits) of the new bit vector.
      Returns:
      a new bit vector of given capacity.

    • getInstance

      public static LongArrayBitVector getInstance()
      Creates a new empty bit vector. No allocation is actually performed.
      Returns:
      a new bit vector with no capacity.

    • ofLength

      public static LongArrayBitVector ofLength(long length)
      Creates a new empty bit vector of given length.
      Parameters:
      length - the size (in bits) of the new bit vector.

    • of

      public static LongArrayBitVector of(int... bit)
      Creates a new bit vector with given bits.
      Parameters:
      bit - a list of bits that will be set in the newly created bit vector.

    • bits

      public long[] bits()
      Description copied from interface: BitVector
      Returns the bits in this bit vector as an array of longs, not to be modified.
      Specified by:
      bits in interface BitVector
      Overrides:
      bits in class AbstractBitVector
      Returns:
      an array of longs whose first BitVector.length() bits contain the bits of this bit vector. The array cannot be modified.

    • length

      public long length()
      Description copied from interface: BitVector
      Returns the number of bits in this bit vector.

      If the number of bits in this bit vector is smaller than or equal to Integer.MAX_VALUE, this method is semantically equivalent to List.size(). In any case, this method is semantically equivalent to Size64.size64(), but it is prefererred.

      Specified by:
      length in interface BitVector
      Returns:
      the number of bits in this bit vector.

    • ensureCapacity

      public LongArrayBitVector ensureCapacity(long numBits)
      Ensures that this bit vector can hold the specified number of bits.

      This method uses LongArrays.grow(long[], int, int) to ensure that there is enough space for the given number of bits. As a consequence, the actual length of the long array allocated might be larger than expected.

      Parameters:
      numBits - the number of bits that this vector must be able to contain.
      Returns:
      this bit vector.

    • length

      public LongArrayBitVector length(long newLength)
      Description copied from interface: BitVector
      Sets the number of bits in this bit vector.

      It is expected that this method will try to allocate exactly the necessary space.

      If the argument fits an integer, this method has the same side effects of BooleanList.size(int). In any case, this method has the same side effects of BigList.size(long), but it is preferred, as it has the advantage of returning this bit vector, thus making it possible to chain methods.

      Specified by:
      length in interface BitVector
      Overrides:
      length in class AbstractBitVector
      Parameters:
      newLength - the new length in bits for this bit vector.
      Returns:
      this bit vector.

    • fill

      public void fill(boolean value)
      Description copied from interface: BitVector
      Sets all bits this bit vector to the given boolean value (optional operation).
      Specified by:
      fill in interface BitVector
      Overrides:
      fill in class AbstractBitVector
      Parameters:
      value - the value (true or false).

    • fill

      public void fill(long from, long to, boolean value)
      Description copied from interface: BitVector
      Fills a range of bits in this bit vector (optional operation).
      Specified by:
      fill in interface BitVector
      Overrides:
      fill in class AbstractBitVector
      Parameters:
      from - the first index (inclusive).
      to - the last index (not inclusive).
      value - the value (true or false).

    • flip

      public void flip()
      Description copied from interface: BitVector
      Flips all bits in this bit vector (optional operation).
      Specified by:
      flip in interface BitVector
      Overrides:
      flip in class AbstractBitVector

    • flip

      public void flip(long from, long to)
      Description copied from interface: BitVector
      Flips a range of bits in this bit vector (optional operation).
      Specified by:
      flip in interface BitVector
      Overrides:
      flip in class AbstractBitVector
      Parameters:
      from - the first index (inclusive).
      to - the last index (not inclusive).

    • trim

      public boolean trim()
      Reduces as must as possible the size of the backing array.
      Returns:
      true if some trimming was actually necessary.

    • clear

      public void clear()
      Sets the size of this bit vector to 0.

      Note that this method does not try to reallocate that backing array. If you want to force that behaviour, call trim() afterwards.

      Specified by:
      clear in interface Collection<Boolean>
      Overrides:
      clear in class AbstractBitVector

    • copy

      public LongArrayBitVector copy(long from, long to)
      Description copied from interface: BitVector
      Returns a copy of a part of this bit vector.
      Specified by:
      copy in interface BitVector
      Overrides:
      copy in class AbstractBitVector
      Parameters:
      from - the starting bit, inclusive.
      to - the ending bit, not inclusive.
      Returns:
      a copy of the part of this bit vector going from bit from (inclusive) to bit to (not inclusive)

    • copy

      public LongArrayBitVector copy()
      Description copied from interface: BitVector
      Returns a copy of this bit vector.
      Specified by:
      copy in interface BitVector
      Overrides:
      copy in class AbstractBitVector
      Returns:
      a copy of this bit vector.

    • fast

      public LongArrayBitVector fast()
      Returns this bit vector.
      Specified by:
      fast in interface BitVector
      Overrides:
      fast in class AbstractBitVector
      Returns:
      this bit vector.

    • copy

      public static LongArrayBitVector copy(BitVector bv)
      Returns a copy of the given bit vector.

      This method uses BitVector.getLong(long, long) on Long.SIZE boundaries to copy at high speed.

      Parameters:
      bv - a bit vector.
      Returns:
      an instance of this class containing a copy of the given vector.

    • getBoolean

      public boolean getBoolean(long index)
      Specified by:
      getBoolean in interface BooleanBigList

    • set

      public boolean set(long index, boolean value)
      Specified by:
      set in interface BooleanBigList
      Overrides:
      set in class AbstractBitVector

    • set

      public void set(long index)
      Description copied from interface: BitVector
      Sets a bit in this bit vector (optional operation).
      Specified by:
      set in interface BitVector
      Overrides:
      set in class AbstractBitVector
      Parameters:
      index - the index of a bit.

    • clear

      public void clear(long index)
      Description copied from interface: BitVector
      Clears a bit in this bit vector (optional operation).
      Specified by:
      clear in interface BitVector
      Overrides:
      clear in class AbstractBitVector
      Parameters:
      index - the index of a bit.

    • add

      public void add(long index, boolean value)
      Specified by:
      add in interface BooleanBigList
      Overrides:
      add in class AbstractBitVector

    • removeBoolean

      public boolean removeBoolean(long index)
      Specified by:
      removeBoolean in interface BooleanBigList
      Overrides:
      removeBoolean in class AbstractBitVector

    • append

      public LongArrayBitVector append(long value, int width)
      Description copied from interface: BitVector
      Appends the less significant bits of a long integer to this bit vector.
      Specified by:
      append in interface BitVector
      Overrides:
      append in class AbstractBitVector
      Parameters:
      value - a value to be appended
      width - the number of less significant bits to be added to this bit vector.
      Returns:
      this bit vector.

    • getLong

      public long getLong(long from, long to)
      Description copied from interface: BitVector
      Returns the specified bit range as a long.

      Note that bit 0 of the returned long will be bit from of this bit vector.

      Implementations are invited to provide high-speed implementations for the case in which from is a multiple of Long.SIZE and to is from + Long.SIZE (or less, in case the vector length is exceeded). This behaviour make it possible to implement high-speed hashing, copies, etc.

      Specified by:
      getLong in interface BitVector
      Overrides:
      getLong in class AbstractBitVector
      Parameters:
      from - the starting bit (inclusive).
      to - the ending bit (exclusive).
      Returns:
      the long value contained in the specified bits.

    • count

      public long count()
      Description copied from interface: BitVector
      Counts the number of bits set to true in this bit vector.
      Specified by:
      count in interface BitVector
      Overrides:
      count in class AbstractBitVector
      Returns:
      the number of bits set to true in this bit vector.

    • nextOne

      public long nextOne(long index)
      Description copied from interface: BitVector
      Returns the position of the first bit set at of after the given position.
      Specified by:
      nextOne in interface BitVector
      Overrides:
      nextOne in class AbstractBitVector
      Parameters:
      index - a bit position.
      Returns:
      the position of the first bit set at or after position index, or -1 if no such bit exists.

    • previousOne

      public long previousOne(long index)
      Description copied from interface: BitVector
      Returns the position of the first bit set strictly before the given position.
      Specified by:
      previousOne in interface BitVector
      Overrides:
      previousOne in class AbstractBitVector
      Parameters:
      index - a bit position.
      Returns:
      the position of the first bit set strictly before position index, or -1 if no such bit exists.

    • nextZero

      public long nextZero(long index)
      Description copied from interface: BitVector
      Returns the position of the first bit unset after the given position.
      Specified by:
      nextZero in interface BitVector
      Overrides:
      nextZero in class AbstractBitVector
      Parameters:
      index - a bit position.
      Returns:
      the first bit unset after position index (inclusive), or -1 if no such bit exists.

    • previousZero

      public long previousZero(long index)
      Description copied from interface: BitVector
      Returns the position of the first bit unset before or at the given position.
      Specified by:
      previousZero in interface BitVector
      Overrides:
      previousZero in class AbstractBitVector
      Parameters:
      index - a bit position.
      Returns:
      the first bit unset before or at the given position, or -1 if no such bit exists.

    • longestCommonPrefixLength

      public long longestCommonPrefixLength(BitVector v)
      Description copied from interface: BitVector
      Returns the length of the greatest common prefix between this and the specified bit vector.
      Specified by:
      longestCommonPrefixLength in interface BitVector
      Overrides:
      longestCommonPrefixLength in class AbstractBitVector
      Parameters:
      v - a bit vector.
      Returns:
      the length of the greatest common prefix.

    • longestCommonPrefixLength

      public long longestCommonPrefixLength(LongArrayBitVector v)

    • and

      public BitVector and(BitVector v)
      Description copied from interface: BitVector
      Performs a logical and between this bit vector and another one, leaving the result in this vector.
      Specified by:
      and in interface BitVector
      Overrides:
      and in class AbstractBitVector
      Parameters:
      v - a bit vector.
      Returns:
      this bit vector.

    • or

      public BitVector or(BitVector v)
      Description copied from interface: BitVector
      Performs a logical or between this bit vector and another one, leaving the result in this bit vector.
      Specified by:
      or in interface BitVector
      Overrides:
      or in class AbstractBitVector
      Parameters:
      v - a bit vector.
      Returns:
      this bit vector.

    • xor

      public BitVector xor(BitVector v)
      Description copied from interface: BitVector
      Performs a logical xor between this bit vector and another one, leaving the result in this vector.
      Specified by:
      xor in interface BitVector
      Overrides:
      xor in class AbstractBitVector
      Parameters:
      v - a bit vector.
      Returns:
      this bit vector.

    • wrap

      public static LongArrayBitVector wrap(long[] array, long size)
      Wraps the given array of longs in a bit vector for the given number of bits.

      Note that all bits in array beyond that of index size must be unset, or an exception will be thrown.

      Parameters:
      array - an array of longs.
      size - the number of bits of the newly created bit vector.
      Returns:
      a bit vector of size size using array as backing array.

    • wrap

      public static LongArrayBitVector wrap(long[] array)
      Wraps the given array of longs in a bit vector.
      Parameters:
      array - an array of longs.
      Returns:
      a bit vector of size array.length * Long.SIZE using array as backing array.

    • clone

      public LongArrayBitVector clone() throws CloneNotSupportedException
      Returns a cloned copy of this bit vector.

      This method is functionally equivalent to copy(), except that copy() trims the backing array.

      Overrides:
      clone in class Object
      Returns:
      a copy of this bit vector.
      Throws:
      CloneNotSupportedException

    • replace

      public LongArrayBitVector replace(LongArrayBitVector bv)

    • replace

      public LongArrayBitVector replace(BitVector bv)
      Description copied from class: AbstractBitVector
      Replaces the content of this bit vector with another bit vector.
      Specified by:
      replace in interface BitVector
      Overrides:
      replace in class AbstractBitVector
      Parameters:
      bv - a bit vector.
      Returns:
      this bit vector.

    • hashCode

      public int hashCode()
      Description copied from interface: BitVector
      Returns a hash code for this bit vector.

      Hash codes for bit vectors are defined as follows: 

       final long length = length();
 long fullLength = length & -Long.SIZE;
 long h = 0x9e3779b97f4a7c13L ^ length;
 for(long i = 0; i < fullLength; i += Long.SIZE) h ^= (h << 5) + getLong(i, i + Long.SIZE) + (h >>> 2);
 if (length != fullLength) h ^= (h << 5) + getLong(fullLength, length) + (h >>> 2);
 (int)((h >>> 32) ^ h);

      The last value is the hash code of the bit vector. This hashing is based on shift-add-xor hashing (M.V. Ramakrishna and Justin Zobel, “Performance in practice of string hashing functions”, Proc. of the Fifth International Conference on Database Systems for Advanced Applications, 1997, pages 215−223).

      The returned value is not a high-quality hash such as Jenkins's, but it can be computed very quickly; in any case, 32 bits are too few for a high-quality hash to be used in large-scale applications.

      Important: all bit vector implementations are required to return the value defined here. The simplest way to obtain this result is to subclass AbstractBitVector.

      Specified by:
      hashCode in interface BitVector
      Specified by:
      hashCode in interface Collection<Boolean>
      Overrides:
      hashCode in class AbstractBitVector
      Returns:
      a hash code for this bit vector.

    • equals

      public boolean equals(Object o)
      Specified by:
      equals in interface Collection<Boolean>
      Overrides:
      equals in class AbstractBitVector

    • equals

      public boolean equals(LongArrayBitVector v)

    • equals

      public boolean equals(LongArrayBitVector v, long start, long end)

    • asLongBigList

      public LongBigList asLongBigList(int width)
      Description copied from interface: BitVector
      Returns a view of this bit vector as a list of nonnegative integers of specified width.

      More formally, getLong(p) will return the nonnegative integer defined by the bits starting at p * width (bit 0, inclusive) and ending at (p + 1) * width (bit width − 1, exclusive).

      Specified by:
      asLongBigList in interface BitVector
      Overrides:
      asLongBigList in class AbstractBitVector
      Parameters:
      width - a bit width.
      Returns:
      a view of this bit vector as a list of nonnegative integers of specified width.