284 lines
12 KiB
C++
284 lines
12 KiB
C++
/*
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**********************************************************************
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* Copyright (C) 1999 Alan Liu and others. All rights reserved.
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**********************************************************************
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* Date Name Description
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* 10/22/99 alan Creation. This is an internal header; it
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* shall not be exported.
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**********************************************************************
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*/
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#ifndef RBBI_BLD_H
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#define RBBI_BLD_H
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#include "rbbi.h"
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#include "uniset.h"
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#include "uvector.h"
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//=======================================================================
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// RuleBasedBreakIterator.Builder
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//=======================================================================
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/**
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* The Builder class has the job of constructing a RuleBasedBreakIterator from a
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* textual description. A Builder is constructed by RuleBasedBreakIterator's
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* constructor, which uses it to construct the iterator itself and then throws it
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* away.
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* <p>The construction logic is separated out into its own class for two primary
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* reasons:
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* <ul><li>The construction logic is quite complicated and large. Separating it
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* out into its own class means the code must only be loaded into memory while a
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* RuleBasedBreakIterator is being constructed, and can be purged after that.
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* <li>There is a fair amount of state that must be maintained throughout the
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* construction process that is not needed by the iterator after construction.
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* Separating this state out into another class prevents all of the functions that
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* construct the iterator from having to have really long parameter lists,
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* (hopefully) contributing to readability and maintainability.</ul>
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* <p>It'd be really nice if this could be an independent class rather than an
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* inner class, because that would shorten the source file considerably, but
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* making Builder an inner class of RuleBasedBreakIterator allows it direct access
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* to RuleBasedBreakIterator's private members, which saves us from having to
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* provide some kind of "back door" to the Builder class that could then also be
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* used by other classes.
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*/
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class RuleBasedBreakIteratorBuilder {
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protected:
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/**
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* A temporary holding place used for calculating the character categories.
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* This object contains UnicodeSet objects.
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*/
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UVector categories;
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/**
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* A table used to map parts of regexp text to lists of character categories,
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* rather than having to figure them out from scratch each time
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*/
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Hashtable expressions;
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/**
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* A temporary holding place for the list of ignore characters
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*/
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UnicodeSet ignoreChars;
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/**
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* A temporary holding place where the forward state table is built
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*/
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UVector tempStateTable;
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/**
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* A list of all the states that have to be filled in with transitions to the
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* next state that is created. Used when building the state table from the
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* regular expressions.
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*/
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UVector decisionPointList;
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/**
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* A UStack for holding decision point lists. This is used to handle nested
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* parentheses and braces in regexps.
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*/
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UStack decisionPointStack;
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/**
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* A list of states that loop back on themselves. Used to handle .*?
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*/
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UVector loopingStates;
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/**
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* Looping states actually have to be backfilled later in the process
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* than everything else. This is where a the list of states to backfill
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* is accumulated. This is also used to handle .*?
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*/
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UVector statesToBackfill;
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/**
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* A list mapping pairs of state numbers for states that are to be combined
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* to the state number of the state representing their combination. Used
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* in the process of making the state table deterministic to prevent
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* infinite recursion.
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*/
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UVector mergeList;
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/**
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* A flag that is used to indicate when the list of looping states can
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* be reset.
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*/
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bool_t clearLoopingStates;
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public:
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/**
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* No special construction is required for the Builder.
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*/
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RuleBasedBreakIteratorBuilder();
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/**
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* This is the main function for setting up the BreakIterator's tables. It
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* just UVectors different parts of the job off to other functions.
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*/
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virtual void buildBreakIterator();
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private:
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/**
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* Thus function has three main purposes:
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* <ul><li>Perform general syntax checking on the description, so the rest of the
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* build code can assume that it's parsing a legal description.
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* <li>Split the description into separate rules
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* <li>Perform variable-name substitutions (so that no one else sees variable names)
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* </ul>
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*/
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virtual UVector buildRuleList(UnicodeString description);
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protected:
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/**
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* This function performs variable-name substitutions. First it does syntax
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* checking on the variable-name definition. If it's syntactically valid, it
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* then goes through the remainder of the description and does a simple
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* find-and-replace of the variable name with its text. (The variable text
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* must be enclosed in either [] or () for this to work.)
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*/
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virtual UnicodeString processSubstitution(UnicodeString substitutionRule, UnicodeString description,
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int32_t startPos);
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/**
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* This function defines a protocol for handling substitution names that
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* are "special," i.e., that have some property beyond just being
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* substitutions. At the RuleBasedBreakIterator level, we have one
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* special substitution name, "<ignore>". Subclasses can override this
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* function to add more. Any special processing that has to go on beyond
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* that which is done by the normal substitution-processing code is done
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* here.
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*/
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virtual void handleSpecialSubstitution(UnicodeString replace, UnicodeString replaceWith,
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int32_t startPos, UnicodeString description);
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/**
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* This function builds the character category table. On entry,
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* tempRuleList is a UVector of break rules that has had variable names substituted.
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* On exit, the charCategoryTable data member has been initialized to hold the
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* character category table, and tempRuleList's rules have been munged to contain
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* character category numbers everywhere a literal character or a [] expression
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* originally occurred.
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*/
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virtual void buildCharCategories(UVector tempRuleList);
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private:
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/**
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* This is the function that builds the forward state table. Most of the real
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* work is done in parseRule(), which is called once for each rule in the
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* description.
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*/
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virtual void buildStateTable(UVector tempRuleList);
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/**
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* This is where most of the work really happens. This routine parses a single
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* rule in the rule description, adding and modifying states in the state
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* table according to the new expression. The state table is kept deterministic
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* throughout the whole operation, although some ugly postprocessing is needed
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* to handle the *? token.
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*/
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virtual void parseRule(UnicodeString rule, bool_t forward);
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/**
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* Update entries in the state table, and merge states when necessary to keep
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* the table deterministic.
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* @param rows The list of rows that need updating (the decision point list)
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* @param pendingChars A character category list, encoded in a String. This is the
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* list of the columns that need updating.
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* @param newValue Update the cells specfied above to contain this value
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*/
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virtual void updateStateTable(UVector rows,
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UnicodeString pendingChars,
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int16_t newValue);
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/**
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* The real work of making the state table deterministic happens here. This function
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* merges a state in the state table (specified by rowNum) with a state that is
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* passed in (newValues). The basic process is to copy the nonzero cells in newStates
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* into the state in the state table (we'll call that oldValues). If there's a
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* collision (i.e., if the same cell has a nonzero value in both states, and it's
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* not the SAME value), then we have to reconcile the collision. We do this by
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* creating a new state, adding it to the end of the state table, and using this
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* function recursively to merge the original two states into a single, combined
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* state. This process may happen recursively (i.e., each successive level may
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* involve collisions). To prevent infinite recursion, we keep a log of merge
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* operations. Any time we're merging two states we've merged before, we can just
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* supply the row number for the result of that merge operation rather than creating
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* a new state just like it.
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* @param rowNum The row number in the state table of the state to be updated
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* @param newValues The state to merge it with.
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* @param rowsBeingUpdated A copy of the list of rows passed to updateStateTable()
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* (itself a copy of the decision point list from parseRule()). Newly-created
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* states get added to the decision point list if their "parents" were on it.
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*/
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virtual void mergeStates(int32_t rowNum,
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int16_t* newValues,
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UVector rowsBeingUpdated);
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/**
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* The merge list is a list of pairs of rows that have been merged somewhere in
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* the process of building this state table, along with the row number of the
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* row containing the merged state. This function looks up a pair of row numbers
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* and returns the row number of the row they combine into. (It returns 0 if
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* this pair of rows isn't in the merge list.)
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*/
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virtual int32_t searchMergeList(int32_t a, int32_t b);
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/**
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* This function is used to update the list of current loooping states (i.e.,
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* states that are controlled by a *? construct). It backfills values from
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* the looping states into unpopulated cells of the states that are currently
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* marked for backfilling, and then updates the list of looping states to be
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* the new list
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* @param newLoopingStates The list of new looping states
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* @param endStates The list of states to treat as end states (states that
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* can exit the loop).
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*/
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virtual void setLoopingStates(UVector newLoopingStates, UVector endStates);
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/**
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* This removes "ending states" and states reachable from them from the
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* list of states to backfill.
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* @param The row number of the state to remove from the backfill list
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*/
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virtual void eliminateBackfillStates(int32_t baseState);
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/**
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* This function completes the backfilling process by actually doing the
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* backfilling on the states that are marked for it
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*/
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virtual void backfillLoopingStates();
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/**
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* This function completes the state-table-building process by doing several
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* postprocessing steps and copying everything into its final resting place
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* in the iterator itself
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* @param forward True if we're working on the forward state table
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*/
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virtual void finishBuildingStateTable(bool_t forward);
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/**
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* This function builds the backward state table from the forward state
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* table and any additional rules (identified by the ! on the front)
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* supplied in the description
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*/
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virtual void buildBackwardsStateTable(UVector tempRuleList);
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protected:
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/**
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* Throws an IllegalArgumentException representing a syntax error in the rule
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* description. The exception's message contains some debugging information.
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* @param message A message describing the problem
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* @param position The position in the description where the problem was
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* discovered
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* @param context The string containing the error
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*/
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virtual void error(UnicodeString message, int32_t position, UnicodeString context);
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};
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#endif
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