Package org.apache.commons.numbers.arrays

Class BitIndexUpdatingInterval

java.lang.Object

org.apache.commons.numbers.arrays.BitIndexUpdatingInterval

All Implemented Interfaces:

UpdatingInterval

final class BitIndexUpdatingInterval
extends java.lang.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 long[]	data	Bit indexes.
private static int	DIVIDE_BY_64	A bit shift to apply to an integer to divided by 64 (2^6).
private int	left	Left bound of the support.
private static long	LONG_MASK	All 64-bits bits set.
private int	offset	Index offset.
private int	right	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	left()	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	previousIndex(int k)	Returns the index of the first bit that is set to true that occurs on or before the specified starting index.
int	right()	The end (inclusive) of the interval.
(package private) void	set(int bitIndex)	Sets the bit at the specified index to true.
UpdatingInterval	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 Detail

LONG_MASK

private static final long LONG_MASK

All 64-bits bits set.

See Also:

Constant Field Values

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:

Constant Field Values

data

private final long[] data

Bit indexes.

offset

private final int offset

Index offset.

left

private int left

Left bound of the support.

right

private int right

Right bound of the support.

Constructor Detail

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 Detail

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