org.terrier.structures
Interface BitIndexPointer

All Superinterfaces:

BitFilePosition, Pointer, org.apache.hadoop.io.Writable

All Known Implementing Classes:

BasicDocumentIndexEntry, BasicLexiconEntry, BlockFieldLexiconEntry, BlockLexiconEntry, DocumentIndexEntry, FieldDocumentIndexEntry, FieldLexiconEntry, SimpleBitIndexPointer, SimpleDocumentIndexEntry

public interface BitIndexPointer
extends BitFilePosition, org.apache.hadoop.io.Writable, Pointer

A pointer implementation for BitPostingIndex structures. It has all the attrbutes of a Pointer. However, BitIndexPointer supports a FileNumber attribute, which allows a single Bit structure to be represented by several underlying files. Moreover, as this is a BitFilePosition, the offset is recorded in terms of bytes (a long) and bits (a byte). In practive, the FileNumber is recorded in 5 spare bits of the "bit" byte, so valid FileNumbers are 0-31 (MAX_FILE_ID).

Since:

3.0

Author:

Craig Macdonald

Field Summary

static byte	BIT_MASK amount to mask byte by to obtain bit offset
static byte	FILE_SHIFT amount to shift byte by to obtain file id
static byte	MAX_FILE_ID largest permissible file id using most implementations

Method Summary

byte	getFileNumber() Returns the file number: 0-32
void	setBitIndexPointer(BitIndexPointer pointer) Update this pointer to reflect the same values as the specified pointer
void	setFileNumber(byte fileId) Set the file number

Methods inherited from interface org.terrier.structures.BitFilePosition

getOffset, getOffsetBits, setOffset, setOffset

Methods inherited from interface org.apache.hadoop.io.Writable

readFields, write

Methods inherited from interface org.terrier.structures.Pointer

getNumberOfEntries, pointerToString, setNumberOfEntries, setPointer

Field Detail

MAX_FILE_ID

static final byte MAX_FILE_ID

largest permissible file id using most implementations

See Also:

Constant Field Values

BIT_MASK

static final byte BIT_MASK

amount to mask byte by to obtain bit offset

See Also:

Constant Field Values

FILE_SHIFT

static final byte FILE_SHIFT

amount to shift byte by to obtain file id

See Also:

Constant Field Values

Method Detail

setBitIndexPointer

void setBitIndexPointer(BitIndexPointer pointer)

Update this pointer to reflect the same values as the specified pointer

Parameters:

pointer - - pointer to use to set the offset, bit offset and file Id parameters.

setFileNumber

void setFileNumber(byte fileId)

Set the file number

getFileNumber

byte getFileNumber()

Returns the file number: 0-32