219 lines
8.8 KiB
C++
219 lines
8.8 KiB
C++
/*
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**********************************************************************
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* Copyright (C) 1999-2000 IBM Corp. All rights reserved.
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**********************************************************************
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* Date Name Description
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* 12/1/99 rgillam Complete port from Java.
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* 01/13/2000 helena Added UErrorCode to ctors.
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**********************************************************************
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*/
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#ifndef DBBI_H
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#define DBBI_H
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#include "unicode/rbbi.h"
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/* forward declaration */
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class DictionaryBasedBreakIteratorTables;
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/**
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* A subclass of RuleBasedBreakIterator that adds the ability to use a dictionary
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* to further subdivide ranges of text beyond what is possible using just the
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* state-table-based algorithm. This is necessary, for example, to handle
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* word and line breaking in Thai, which doesn't use spaces between words. The
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* state-table-based algorithm used by RuleBasedBreakIterator is used to divide
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* up text as far as possible, and then contiguous ranges of letters are
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* repeatedly compared against a list of known words (i.e., the dictionary)
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* to divide them up into words.
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*
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* DictionaryBasedBreakIterator uses the same rule language as RuleBasedBreakIterator,
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* but adds one more special substitution name: <dictionary>. This substitution
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* name is used to identify characters in words in the dictionary. The idea is that
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* if the iterator passes over a chunk of text that includes two or more characters
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* in a row that are included in <dictionary>, it goes back through that range and
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* derives additional break positions (if possible) using the dictionary.
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*
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* DictionaryBasedBreakIterator is also constructed with the filename of a dictionary
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* file. It follows a prescribed search path to locate the dictionary (right now,
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* it looks for it in /com/ibm/text/resources in each directory in the classpath,
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* and won't find it in JAR files, but this location is likely to change). The
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* dictionary file is in a serialized binary format. We have a very primitive (and
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* slow) BuildDictionaryFile utility for creating dictionary files, but aren't
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* currently making it public. Contact us for help.
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* <p>
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* <b> NOTE </b> The DictionaryBasedIterator class is still under development. The
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* APIs are not in stable condition yet.
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*/
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class U_I18N_API DictionaryBasedBreakIterator : public RuleBasedBreakIterator {
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private:
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/**
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* a temporary hiding place for the number of dictionary characters in the
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* last range passed over by next()
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*/
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int32_t dictionaryCharCount;
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/**
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* when a range of characters is divided up using the dictionary, the break
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* positions that are discovered are stored here, preventing us from having
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* to use either the dictionary or the state table again until the iterator
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* leaves this range of text
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*/
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int32_t* cachedBreakPositions;
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/**
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* The number of elements in cachedBreakPositions
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*/
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int32_t numCachedBreakPositions;
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/**
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* if cachedBreakPositions is not null, this indicates which item in the
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* cache the current iteration position refers to
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*/
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int32_t positionInCache;
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/**
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* Class ID
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*/
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static char fgClassID;
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public:
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/**=======================================================================
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* Create a dictionary based break boundary detection iterator.
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* @param tablesImage The location for the dictionary to be loaded into memory
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* @param dictionaryFilename The name of the dictionary file
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* @param status the error code status
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* @return A dictionary based break detection iterator. The UErrorCode& status
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* parameter is used to return status information to the user.
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* To check whether the construction succeeded or not, you should check
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* the value of U_SUCCESS(err). If you wish more detailed information, you
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* can check for informational error results which still indicate success. For example,
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* U_FILE_ACCESS_ERROR will be returned if the file does not exist.
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* The caller owns the returned object and is responsible for deleting it.
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======================================================================= */
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DictionaryBasedBreakIterator(const void* tablesImage, char* dictionaryFilename, UErrorCode& status);
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//=======================================================================
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// boilerplate
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//=======================================================================
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/**
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* Destructor
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*/
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virtual ~DictionaryBasedBreakIterator();
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/**
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* Assignment operator. Sets this iterator to have the same behavior,
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* and iterate over the same text, as the one passed in.
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*/
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DictionaryBasedBreakIterator& operator=(const DictionaryBasedBreakIterator& that);
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/**
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* Returns a newly-constructed RuleBasedBreakIterator with the same
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* behavior, and iterating over the same text, as this one.
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*/
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virtual BreakIterator* clone(void) const;
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//=======================================================================
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// BreakIterator overrides
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//=======================================================================
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/**
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* Advances the iterator backwards, to the last boundary preceding this one.
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* @return The position of the last boundary position preceding this one.
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*/
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virtual int32_t previous(void);
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/**
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* Sets the iterator to refer to the first boundary position following
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* the specified position.
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* @offset The position from which to begin searching for a break position.
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* @return The position of the first break after the current position.
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*/
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virtual int32_t following(int32_t offset);
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/**
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* Sets the iterator to refer to the last boundary position before the
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* specified position.
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* @offset The position to begin searching for a break from.
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* @return The position of the last boundary before the starting position.
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*/
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virtual int32_t preceding(int32_t offset);
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/**
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* Returns a unique class ID POLYMORPHICALLY. Pure virtual override.
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* This method is to implement a simple version of RTTI, since not all
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* C++ compilers support genuine RTTI. Polymorphic operator==() and
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* clone() methods call this method.
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*
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* @return The class ID for this object. All objects of a
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* given class have the same class ID. Objects of
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* other classes have different class IDs.
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*/
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virtual UClassID getDynamicClassID(void) const;
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/**
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* Returns the class ID for this class. This is useful only for
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* comparing to a return value from getDynamicClassID(). For example:
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*
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* Base* polymorphic_pointer = createPolymorphicObject();
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* if (polymorphic_pointer->getDynamicClassID() ==
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* Derived::getStaticClassID()) ...
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*
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* @return The class ID for all objects of this class.
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*/
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static UClassID getStaticClassID(void);
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protected:
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//=======================================================================
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// implementation
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//=======================================================================
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/**
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* This method is the actual implementation of the next() method. All iteration
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* vectors through here. This method initializes the state machine to state 1
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* and advances through the text character by character until we reach the end
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* of the text or the state machine transitions to state 0. We update our return
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* value every time the state machine passes through a possible end state.
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*/
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virtual int32_t handleNext(void);
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/**
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* dumps the cache of break positions (usually in response to a change in
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* position of some sort)
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*/
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virtual void reset(void);
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private:
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/**
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* This is the function that actually implements the dictionary-based
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* algorithm. Given the endpoints of a range of text, it uses the
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* dictionary to determine the positions of any boundaries in this
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* range. It stores all the boundary positions it discovers in
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* cachedBreakPositions so that we only have to do this work once
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* for each time we enter the range.
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*/
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void divideUpDictionaryRange(int32_t startPos, int32_t endPos);
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/**
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* Used by the tables object to increment the count of dictionary characters
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* during iteration
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*/
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void bumpDictionaryCharCount(void);
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friend class DictionaryBasedBreakIteratorTables;
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};
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inline UClassID DictionaryBasedBreakIterator::getDynamicClassID(void) const {
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return RuleBasedBreakIterator::getStaticClassID();
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}
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inline UClassID DictionaryBasedBreakIterator::getStaticClassID(void) {
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return (UClassID)(&fgClassID);
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}
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inline void DictionaryBasedBreakIterator::bumpDictionaryCharCount(void) {
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++dictionaryCharCount;
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}
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#endif
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