org.exist.numbering
Class DLNBase

java.lang.Object
  org.exist.numbering.DLNBase

Direct Known Subclasses:

DLN

public class DLNBase
extends Object

Base class representing a node id in the form of a dynamic level number (DLN). See DLN. DLNBase handles the efficient binary encoding of node ids. Level values are stored consecutively, using a fixed prefix free encoding. The number of units to be used for encoding a single level value is dynamically adjusted. We start with one unit and use its n - 1 lower bits. If the number exceeds the lower bits, we add another unit and set the highest bit to 1. This process is repeated for larger numbers. As a result, the first 1 bits of a level id indicate the number of fixed-size units used for encoding a level id. We thus don't need separator bits between the units themselves.

Author:

wolf

Field Summary

static int[]	BIT_MASK
static int	BITS_PER_UNIT The default number of bits used per fixed size unit.

Constructor Summary

DLNBase()

DLNBase(byte prefixLen, DLNBase previous, short bitCnt, VariableByteInput is)

DLNBase(DLNBase dln)

DLNBase(int units, byte[] data, int startOffset)

DLNBase(short bitCnt, VariableByteInput is)

Method Summary

void	addLevelId(int levelId, boolean isSubLevel) Adds a new level to the node id, using levelId as initial value.
int	compareBits(DLNBase other, int bitCount)
String	debug()
void	decrementLevelId()
boolean	equals(DLNBase other)
static int	getLengthInBytes(int units, byte[] data, int startOffset)
int	getLevelCount(int startOffset) Returns the number of level in this id, which corresponds to the depth at which the node occurs within the node tree.
int	getLevelId(int startBit) Returns the id starting at offset.
int[]	getLevelIds() Return all level ids converted to int.
int	getSubLevelCount(int startOffset) Returns the number of sub-levels in the id starting at startOffset.
void	incrementLevelId() Increments the last level id by one.
boolean	isLevelSeparator(int index)
int	lastLevelOffset() Find the last level in the id and return its offset.
void	serialize(byte[] data, int offset)
void	setLevelId(int offset, int levelId) Set the level id which starts at offset to the given id value.
int	size() Returns the size of this id by counting the bytes used to encode it.
boolean	startsWith(DLNBase other) Checks if the current DLN starts with the same bit sequence as other.
String	toBitString()
static String	toBitString(byte b) Returns a string showing the bit representation of the given byte.
String	toString()
int	units() Returns the number of units currently used to encode the id.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

BITS_PER_UNIT

public static final int BITS_PER_UNIT

The default number of bits used per fixed size unit.

See Also:

Constant Field Values

BIT_MASK

public static final int[] BIT_MASK

Constructor Detail

DLNBase

public DLNBase()

DLNBase

public DLNBase(DLNBase dln)

DLNBase

public DLNBase(int units,
               byte[] data,
               int startOffset)

DLNBase

public DLNBase(short bitCnt,
               VariableByteInput is)
        throws IOException

Throws:

IOException

DLNBase

public DLNBase(byte prefixLen,
               DLNBase previous,
               short bitCnt,
               VariableByteInput is)
        throws IOException

Throws:

IOException

Method Detail

setLevelId

public void setLevelId(int offset,
                       int levelId)

Set the level id which starts at offset to the given id value.

Parameters:

offset -

levelId -

addLevelId

public void addLevelId(int levelId,
                       boolean isSubLevel)

Adds a new level to the node id, using levelId as initial value.

Parameters:

levelId - initial value

incrementLevelId

public void incrementLevelId()

Increments the last level id by one.

decrementLevelId

public void decrementLevelId()

getLevelId

public int getLevelId(int startBit)

Returns the id starting at offset.

Parameters:

startBit -

Returns:

the level id

units

public int units()

Returns the number of units currently used to encode the id. The size of a single unit is given by BITS_PER_UNIT.

Returns:

the number of units

size

public int size()

Returns the size of this id by counting the bytes used to encode it.

Returns:

the size in bytes

isLevelSeparator

public boolean isLevelSeparator(int index)

getLevelCount

public int getLevelCount(int startOffset)

Returns the number of level in this id, which corresponds to the depth at which the node occurs within the node tree.

Returns:

the number of levels in this id

getSubLevelCount

public int getSubLevelCount(int startOffset)

Returns the number of sub-levels in the id starting at startOffset. This is required to determine where a node can be inserted.

Parameters:

startOffset -

Returns:

number of sub-levels

getLevelIds

public int[] getLevelIds()

Return all level ids converted to int.

Returns:

all level ids in this node id.

lastLevelOffset

public int lastLevelOffset()

Find the last level in the id and return its offset.

Returns:

start-offset of the last level id.

serialize

public void serialize(byte[] data,
                      int offset)

getLengthInBytes

public static int getLengthInBytes(int units,
                                   byte[] data,
                                   int startOffset)

equals

public boolean equals(DLNBase other)

compareBits

public int compareBits(DLNBase other,
                       int bitCount)

startsWith

public boolean startsWith(DLNBase other)

Checks if the current DLN starts with the same bit sequence as other. This is used to test ancestor-descendant relationships.

Parameters:

other -

debug

public String debug()

toString

public String toString()

Overrides:

toString in class Object

toBitString

public String toBitString()

toBitString

public static final String toBitString(byte b)

Returns a string showing the bit representation of the given byte.

Parameters:

b - the byte to display

Returns:

string representation