source: trunk/yao/share/antlr-2.7.7/lib/cpp/antlr/TokenBuffer.hpp @ 1

#ifndef INC_TokenBuffer_hpp__
#define INC_TokenBuffer_hpp__

/* ANTLR Translator Generator
 * Project led by Terence Parr at http://www.jGuru.com
 * Software rights: http://www.antlr.org/license.html
 *
 * $Id: //depot/code/org.antlr/release/antlr-2.7.7/lib/cpp/antlr/TokenBuffer.hpp#2 $
 */

#include <antlr/config.hpp>
#include <antlr/TokenStream.hpp>
#include <antlr/CircularQueue.hpp>

#ifdef ANTLR_CXX_SUPPORTS_NAMESPACE
namespace antlr {
#endif

/**A Stream of Token objects fed to the parser from a TokenStream that can
 * be rewound via mark()/rewind() methods.
 * <p>
 * A dynamic array is used to buffer up all the input tokens.  Normally,
 * "k" tokens are stored in the buffer.  More tokens may be stored during
 * guess mode (testing syntactic predicate), or when LT(i>k) is referenced.
 * Consumption of tokens is deferred.  In other words, reading the next
 * token is not done by conume(), but deferred until needed by LA or LT.
 * <p>
 *
 * @todo: see if we can integrate this one with InputBuffer into one template
 * or so.
 *
 * @see antlr.Token
 * @see antlr.TokenStream
 * @see antlr.TokenQueue
 */
class ANTLR_API TokenBuffer {
public:
        /** Create a token buffer */
        TokenBuffer(TokenStream& input_);
        virtual ~TokenBuffer();

        /// Reset the input buffer to empty state
        inline void reset( void )
        {
                nMarkers = 0;
                markerOffset = 0;
                numToConsume = 0;
                queue.clear();
        }

        /** Get a lookahead token value */
        int LA( unsigned int i );

        /** Get a lookahead token */
        RefToken LT( unsigned int i );

        /** Return an integer marker that can be used to rewind the buffer to
         * its current state.
         */
        unsigned int mark();

        /**Rewind the token buffer to a marker.
         * @param mark Marker returned previously from mark()
         */
        void rewind(unsigned int mark);

        /** Mark another token for deferred consumption */
        inline void consume()
        {
                numToConsume++;
        }

        /// Return the number of entries in the TokenBuffer
        virtual unsigned int entries() const;

private:
        /** Ensure that the token buffer is sufficiently full */
        void fill(unsigned int amount);
        /** Sync up deferred consumption */
        void syncConsume();

protected:
        /// Token source
        TokenStream& input;

        /// Number of active markers
        unsigned int nMarkers;

        /// Additional offset used when markers are active
        unsigned int markerOffset;

        /// Number of calls to consume() since last LA() or LT() call
        unsigned int numToConsume;

        /// Circular queue with Tokens
        CircularQueue<RefToken> queue;

private:
        TokenBuffer(const TokenBuffer& other);
        const TokenBuffer& operator=(const TokenBuffer& other);
};

/** Sync up deferred consumption */
inline void TokenBuffer::syncConsume()
{
        if (numToConsume > 0)
        {
                if (nMarkers > 0)
                        markerOffset += numToConsume;
                else
                        queue.removeItems( numToConsume );

                numToConsume = 0;
        }
}

#ifdef ANTLR_CXX_SUPPORTS_NAMESPACE
}
#endif

#endif //INC_TokenBuffer_hpp__