org.jscience.linguistics.search
Class ShiftOr

java.lang.Object
  org.jscience.linguistics.search.StringSearch
      org.jscience.linguistics.search.ShiftOr

Direct Known Subclasses:

ShiftOrClasses, ShiftOrWildcards

public class ShiftOr
extends StringSearch

An implementation of the Shift-Or algorithm by Ricardo Baeza-Yates and Gaston Gonnet as outlined in "A New Approach to Text Searching" (appeared in Proceedings of the 12th International Conference on Research and Development in Datum Retrieval). The Shift-Or algorithm is a bit-parallel algorithm.

The Shift-Or algorithm is not the fastest and by itself slower than String's indexOf method. It's usefulness comes from it's ability to support character classes and searching with errors at the same speed.

It's searchChars(char[],int,int,char[],Object) method is extremely slow in the Sun Java Virtual Machines. If possible, the searchBytes(byte[],int,int,byte[],Object) methods should be preferred. Because the main loop is also used by the ShiftOrWildcards class, the implementation cannot skip forward until the first character matches (as in the original algorithm).

This implementation currently limited to at most 31 characters because Java has no unsigned int type. An implementation that used long has proved to take twice the amount of time.

 Preprocessing: O(n + ∑) time

 Searching    : O(mn / log n) (worst case and average)

See Also:

ftp://sunsite.dcc.uchile.cl/pub/users/rbaeza/papers/CACM92.ps.gz , http://citeseer.nj.nec.com/50265.html , ShiftOrWildcards, ShiftOrClasses, ShiftOrMismatches

Nested Class Summary

Nested classes/interfaces inherited from class org.jscience.linguistics.search.StringSearch

StringSearch.Dispatch, StringSearch.ReflectionDispatch

Field Summary

Fields inherited from class org.jscience.linguistics.search.StringSearch

activeDispatch, useNative

Constructor Summary

ShiftOr()
Constructor for ShiftOr.

Method Summary

java.lang.Object	processBytes(byte[] pattern) Pre-processing of the pattern.
java.lang.Object	processChars(char[] pattern) Pre-processing of the pattern.
int	searchBytes(byte[] text, int textStart, int textEnd, byte[] pattern, java.lang.Object processed) Returns the position in the text at which the pattern was found.
int	searchChars(char[] text, int textStart, int textEnd, char[] pattern, java.lang.Object processed) Returns the index of the pattern in the text using the pre-processed Object.

Methods inherited from class org.jscience.linguistics.search.StringSearch

createCharIntMap, createCharIntMap, equals, hashCode, index, processString, searchBytes, searchBytes, searchBytes, searchBytes, searchBytes, searchChars, searchChars, searchChars, searchChars, searchChars, searchString, searchString, searchString, searchString, searchString, searchString, toString, toStringBuffer, usesNative, usesReflection

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

ShiftOr

public ShiftOr()

Constructor for ShiftOr. Note that it is not required to create multiple instances.

Method Detail

processBytes

public java.lang.Object processBytes(byte[] pattern)

Pre-processing of the pattern. The pattern may not exceed 31 bytes in length. If it does, only it's first 31 bytes are processed which might lead to unexpected results. Returns an int array.

Specified by:

processBytes in class StringSearch

Parameters:

pattern - the byte array containing the pattern, may not be null

Returns:

an Object

See Also:

StringSearch.processBytes(byte[])

processChars

public java.lang.Object processChars(char[] pattern)

Pre-processing of the pattern. The pattern may not exceed 31 characters in length. If it does, only it's first 31 characters are processed which might lead to unexpected results. Returns a CharIntMap.

Specified by:

processChars in class StringSearch

Parameters:

pattern - the pattern

Returns:

an Object

See Also:

StringSearch.processChars(char[])

searchBytes

public int searchBytes(byte[] text,
                       int textStart,
                       int textEnd,
                       byte[] pattern,
                       java.lang.Object processed)

Description copied from class: StringSearch

Returns the position in the text at which the pattern was found. Returns -1 if the pattern was not found.

Specified by:

searchBytes in class StringSearch

Parameters:

text - text the byte array containing the text, may not be null

textStart - at which position in the text the comparing should start

textEnd - at which position in the text comparing should stop

pattern - the pattern to search for, may not be null

processed - an Object as returned from StringSearch.processBytes(byte[]), may not be null

Returns:

the position in the text or -1 if the pattern was not found

See Also:

StringSearch.searchBytes(byte[], int,int,byte[],java.lang.Object)

searchChars

public int searchChars(char[] text,
                       int textStart,
                       int textEnd,
                       char[] pattern,
                       java.lang.Object processed)

Description copied from class: StringSearch

Returns the index of the pattern in the text using the pre-processed Object. Returns -1 if the pattern was not found.

Specified by:

searchChars in class StringSearch

Parameters:

text - the String containing the text, may not be null

textStart - at which position in the text the comparing should start

textEnd - at which position in the text comparing should stop

pattern - the pattern to search for, may not be null

processed - an Object as returned from StringSearch.processChars(char[]) or StringSearch.processString(String), may not be null

Returns:

the position in the text or -1 if the pattern was not found

See Also:

StringSearch.searchChars(char[], int,int,char[],Object)