Package org.apache.commons.collections4.bloomfilter

Class BitMaps

  • public class BitMaps
extends java.lang.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

    • Method Summary

      All Methods Static Methods Concrete Methods 
      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.
      static int numberOfBitMaps​(int numberOfBits)
      Calculates the number of bit maps (longs) required for the numberOfBits 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

    • Method Detail

      • 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:
        java.lang.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:
        java.lang.ArithmeticException - if the divisor is zero
        See Also:
        Long.remainderUnsigned(long, long)

      • 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.

      • 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:
        java.lang.IndexOutOfBoundsException - if bitIndex specifies a bit not in the range being tracked.