Class BitIndexUpdatingInterval

java.lang.Object
org.apache.commons.numbers.arrays.BitIndexUpdatingInterval
All Implemented Interfaces:
UpdatingInterval

final class BitIndexUpdatingInterval extends Object implements UpdatingInterval
An UpdatingInterval backed by a fixed size of bits.

This is a specialised class to implement a reduced API similar to a BitSet. It uses no bounds range checks and supports only the methods required to implement the UpdatingInterval API.

An offset is supported to allow the fixed size to cover a range of indices starting above 0 with the most efficient usage of storage.

See the BloomFilter code in Commons Collections for use of long[] data to store bits.

Since:
1.2
  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    private final long[]
    Bit indexes.
    private static final int
    A bit shift to apply to an integer to divided by 64 (2^6).
    private int
    Left bound of the support.
    private static final long
    All 64-bits bits set.
    private final int
    Index offset.
    private int
    Right bound of the support.
  • Constructor Summary

    Constructors
    Modifier
    Constructor
    Description
    (package private)
    BitIndexUpdatingInterval(int left, int right)
    Create an instance to store indices within the range [left, right].
    private
    BitIndexUpdatingInterval(long[] data, int offset, int left, int right)
    Create an instance with the range [left, right] and reusing the provided index data.
  • Method Summary

    Modifier and Type
    Method
    Description
    private 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.
    private 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.
    int
    The start (inclusive) of the interval.
    private int
    nextIndex(int k)
    Returns the index of the first bit that is set to true that occurs on or after the specified starting index.
    private int
    Returns the index of the first bit that is set to true that occurs on or before the specified starting index.
    int
    The end (inclusive) of the interval.
    (package private) void
    set(int bitIndex)
    Sets the bit at the specified index to true.
    splitLeft(int ka, int kb)
    Split the interval using two splitting indices.
    int
    updateLeft(int k)
    Update the left bound of the interval so k <= left.
    int
    updateRight(int k)
    Update the right bound of the interval so right <= k.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
  • Field Details

    • LONG_MASK

      private static final long LONG_MASK
      All 64-bits bits set.
      See Also:
    • 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:
    • data

      private final long[] data
      Bit indexes.
    • offset

      private final int offset
      Index offset.
    • left

      private int left
      Left bound of the support.
  • Constructor Details

    • BitIndexUpdatingInterval

      BitIndexUpdatingInterval(int left, int right)
      Create an instance to store indices within the range [left, right]. The range is not validated.
      Parameters:
      left - Lower bound (inclusive).
      right - Upper bound (inclusive).
    • BitIndexUpdatingInterval

      private BitIndexUpdatingInterval(long[] data, int offset, int left, int right)
      Create an instance with the range [left, right] and reusing the provided index data.
      Parameters:
      data - Data.
      offset - Index offset.
      left - Lower bound (inclusive).
      right - Upper bound (inclusive).
  • Method Details

    • getLongIndex

      private 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.
    • getLongBit

      private 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
    • set

      void set(int bitIndex)
      Sets the bit at the specified index to true.

      Warning: This has no range checks.

      Parameters:
      bitIndex - the bit index (assumed to be positive)
    • nextIndex

      private int nextIndex(int k)
      Returns the index of the first bit that is set to true that occurs on or after the specified starting index.

      Warning: This has no range checks. It is assumed that left <= k <= right, that is there is a set bit on or after k.

      Parameters:
      k - Index to start checking from (inclusive).
      Returns:
      the index of the next set bit
    • previousIndex

      private int previousIndex(int k)
      Returns the index of the first bit that is set to true that occurs on or before the specified starting index.

      Warning: This has no range checks. It is assumed that left <= k <= right, that is there is a set bit on or before k.

      Parameters:
      k - Index to start checking from (inclusive).
      Returns:
      the index of the previous set bit
    • left

      public int left()
      Description copied from interface: UpdatingInterval
      The start (inclusive) of the interval.
      Specified by:
      left in interface UpdatingInterval
      Returns:
      start of the interval
    • right

      public int right()
      Description copied from interface: UpdatingInterval
      The end (inclusive) of the interval.
      Specified by:
      right in interface UpdatingInterval
      Returns:
      end of the interval
    • updateLeft

      public int updateLeft(int k)
      Description copied from interface: UpdatingInterval
      Update the left bound of the interval so k <= left.

      Note: Requires left < k <= right, i.e. there exists a valid interval above the index.

      
       l-----------k----------r
                   |--> l
       
      Specified by:
      updateLeft in interface UpdatingInterval
      Parameters:
      k - Index to start checking from (inclusive).
      Returns:
      the new left
    • updateRight

      public int updateRight(int k)
      Description copied from interface: UpdatingInterval
      Update the right bound of the interval so right <= k.

      Note: Requires left <= k < right, i.e. there exists a valid interval below the index.

      
       l-----------k----------r
              r <--|
       
      Specified by:
      updateRight in interface UpdatingInterval
      Parameters:
      k - Index to start checking from (inclusive).
      Returns:
      the new right
    • splitLeft

      public UpdatingInterval splitLeft(int ka, int kb)
      Description copied from interface: UpdatingInterval
      Split the interval using two splitting indices. Returns the left interval that occurs before the specified split index ka, and updates the current interval left bound to after the specified split index kb.

      Note: Requires left < ka <= kb < right, i.e. there exists a valid interval both above and below the splitting indices.

      
       l-----------ka-kb----------r
            r1 <--|     |--> l1
      
       r1 < ka
       l1 > kb
       

      If ka <= left or kb >= right the result is undefined.

      Specified by:
      splitLeft in interface UpdatingInterval
      Parameters:
      ka - Split index.
      kb - Split index.
      Returns:
      the left interval