Package org.apache.commons.collections4.bloomfilter

Class BitMaps

java.lang.Object
org.apache.commons.collections4.bloomfilter.BitMaps
public class BitMaps extends Object
Contains functions to convert int indices into Bloom filter bit positions and visa versa.

The functions view an array of longs as a collection of bit maps each containing 64 bits. The bits are arranged in memory as a little-endian long value. This matches the requirements of the BitMapExtractor interface.

Since:
4.5.0-M2

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    private static final int
    DIVIDE_BY_64
    A bit shift to apply to an integer to divided by 64 (2^6).

  • Constructor Summary

    Constructors
    Modifier
    Constructor
    Description
    private
    BitMaps()
    Do not instantiate.

  • Method Summary

    Modifier and Type
    Method
    Description
    static boolean
    contains(long[] bitMaps, int bitIndex)
    Checks if the specified index bit is enabled in the array of bit maps.
    static long
    getLongBit(int bitIndex)
    Gets the filter bit mask for the specified bit index assuming the filter is using 64-bit longs to store bits starting at index 0.
    static int
    getLongIndex(int bitIndex)
    Gets the filter index for the specified bit index assuming the filter is using 64-bit longs to store bits starting at index 0.
    static int
    mod(long dividend, int divisor)
    Performs a modulus calculation on an unsigned long and a positive integer divisor.
    (package private) static long[]
    newBitMap(int numberOfBits)
    Creates a new bitmap for the number of bit maps (longs) required for the numberOfBits parameter.
    (package private) static long[]
    newBitMap(Shape shape)
    Creates a new bitmap for given shape parameter.
    static int
    numberOfBitMaps(int numberOfBits)
    Calculates the number of bit maps (longs) required for the numberOfBits parameter.
    (package private) static int
    numberOfBitMaps(Shape shape)
    Calculates the number of bit maps (longs) required for the shape parameter.
    static void
    set(long[] bitMaps, int bitIndex)
    Sets the bit in the bit maps.

    Methods inherited from class java.lang.Object

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

  • Field Details

    • DIVIDE_BY_64

      private static final int DIVIDE_BY_64
      A bit shift to apply to an integer to divided by 64 (2^6).
      See Also:

  • Constructor Details

    • BitMaps

      private BitMaps()
      Do not instantiate.

  • Method Details

    • contains

      public static boolean contains(long[] bitMaps, int bitIndex)
      Checks if the specified index bit is enabled in the array of bit maps.

      If the bit specified by bitIndex is not in the bit map false is returned.

      Parameters:
      bitMaps - The array of bit maps.
      bitIndex - the index of the bit to locate.
      Returns:
      true if the bit is enabled, false otherwise.
      Throws:
      IndexOutOfBoundsException - if bitIndex specifies a bit not in the range being tracked.

    • getLongBit

      public static long getLongBit(int bitIndex)
      Gets the filter bit mask for the specified bit index assuming the filter is using 64-bit longs to store bits starting at index 0. The returned value is a long with only 1 bit set.

      The index is assumed to be positive. For a positive index the result will match 1L << (bitIndex % 64).

      If the input is negative the behavior is not defined.

      Parameters:
      bitIndex - the bit index (assumed to be positive)
      Returns:
      the filter bit

    • getLongIndex

      public static int getLongIndex(int bitIndex)
      Gets the filter index for the specified bit index assuming the filter is using 64-bit longs to store bits starting at index 0.

      The index is assumed to be positive. For a positive index the result will match bitIndex / 64.

      The divide is performed using bit shifts. If the input is negative the behavior is not defined.

      Parameters:
      bitIndex - the bit index (assumed to be positive)
      Returns:
      the index of the bit map in an array of bit maps.

    • mod

      public static int mod(long dividend, int divisor)
      Performs a modulus calculation on an unsigned long and a positive integer divisor.

      This method computes the same result as Long.remainderUnsigned(long, long) but assumes that the divisor is an integer in the range 1 to 231 - 1 inclusive, that is a strictly positive integer size.

      If the divisor is negative the behavior is not defined.

      Parameters:
      dividend - an unsigned long value to calculate the modulus of.
      divisor - the divisor for the modulus calculation, must be strictly positive.
      Returns:
      the remainder or modulus value.
      Throws:
      ArithmeticException - if the divisor is zero
      See Also:

    • newBitMap

      static long[] newBitMap(int numberOfBits)
      Creates a new bitmap for the number of bit maps (longs) required for the numberOfBits parameter.

      If the input is negative the behavior is not defined.

      Parameters:
      numberOfBits - the number of bits to store in the array of bit maps.
      Returns:
      a new bitmap.

    • newBitMap

      static long[] newBitMap(Shape shape)
      Creates a new bitmap for given shape parameter.
      Parameters:
      shape - the shape.
      Returns:
      a new bitmap.

    • numberOfBitMaps

      public static int numberOfBitMaps(int numberOfBits)
      Calculates the number of bit maps (longs) required for the numberOfBits parameter.

      If the input is negative the behavior is not defined.

      Parameters:
      numberOfBits - the number of bits to store in the array of bit maps.
      Returns:
      the number of bit maps necessary.

    • numberOfBitMaps

      static int numberOfBitMaps(Shape shape)
      Calculates the number of bit maps (longs) required for the shape parameter.
      Parameters:
      shape - the shape.
      Returns:
      the number of bit maps necessary.

    • set

      public static void set(long[] bitMaps, int bitIndex)
      Sets the bit in the bit maps.

      Does not perform range checking

      Parameters:
      bitMaps - The array of bit maps.
      bitIndex - the index of the bit to set.
      Throws:
      IndexOutOfBoundsException - if bitIndex specifies a bit not in the range being tracked.