BitIndexPointer (Terrier Information Retrieval Platform 5.5 API)

All Superinterfaces:

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

All Known Implementing Classes:

BasicDocumentIndexEntry, BasicLexiconEntry, DocumentIndexEntry, FieldDocumentIndexEntry, FieldLexiconEntry, MultiDocumentEntry, NonIncrementalDocumentIndexEntry, SimpleBitIndexPointer, SimpleDocumentIndexEntry, Tr3BlockFieldLexiconEntry, Tr3BlockLexiconEntry, Tr4BasicLexiconEntry, Tr4FieldLexiconEntry
```
public interface BitIndexPointer
extends BitFilePosition, org.apache.hadoop.io.Writable, Pointer
```
A Pointer specialisation for some PostingIndex structures. It has all the methods of a Pointer. However, some implementations (e.g. BitPostingIndex) supports a "file number" attribute, which allows a single index data 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 practice, the "file number" is recorded in 5 spare bits of the "bit" byte, so valid "file numbers" are 0 - 31 (see MAX_FILE_ID).

Since:

3.0

Author:

Craig Macdonald

Field Summary

Fields
Modifier and Type	Field	Description
`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

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`byte`	`getFileNumber()`	Returns the file number (byte value in the 0-31 range)
`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.terrier.structures.Pointer
getNumberOfEntries, pointerToString, setNumberOfEntries, setPointer

Methods inherited from interface org.apache.hadoop.io.Writable
readFields, write

- 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 - the pointer to use to set the byte offset, bit offset and file number parameters.
  - setFileNumber
```
void setFileNumber(byte fileId)
```
    Set the file number.
    
    Parameters:
    
    fileId - the file number.
  - getFileNumber
```
byte getFileNumber()
```
    Returns the file number (byte value in the 0-31 range)
    
    Returns:
    
    the file number (byte value in the 0-31 range)