TokenBuffer.cpp

/* ANTLR Translator Generator
 * Project led by Terence Parr at http://www.jGuru.com
 * Software rights: http://www.antlr.org/license.html
 *
 * $Id$
 */
 
#include "antlr/TokenBuffer.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>
 *
 * @see antlr.Token
 * @see antlr.TokenStream
 * @see antlr.TokenQueue
 */
 
/** Create a token buffer */
TokenBuffer::TokenBuffer( TokenStream& inp )
: input(inp)
, nMarkers(0)
, markerOffset(0)
, numToConsume(0)
{
}
 
TokenBuffer::~TokenBuffer( void )
{
}
 
/** Ensure that the token buffer is sufficiently full */
void TokenBuffer::fill(unsigned int amount)
{
        syncConsume();
        // Fill the buffer sufficiently to hold needed tokens
        while (queue.entries() < (amount + markerOffset))
        {
                // Append the next token
                queue.append(input.nextToken());
        }
}
 
/** Get a lookahead token value */
int TokenBuffer::LA(unsigned int i)
{
        fill(i);
        return queue.elementAt(markerOffset+i-1)->getType();
}
 
/** Get a lookahead token */
RefToken TokenBuffer::LT(unsigned int i)
{
        fill(i);
        return queue.elementAt(markerOffset+i-1);
}
 
/** Return an integer marker that can be used to rewind the buffer to
 * its current state.
 */
unsigned int TokenBuffer::mark()
{
        syncConsume();
        nMarkers++;
        return markerOffset;
}
 
/**Rewind the token buffer to a marker.
 * @param mark Marker returned previously from mark()
 */
void TokenBuffer::rewind(unsigned int mark)
{
        syncConsume();
        markerOffset=mark;
        nMarkers--;
}
 
/// Get number of non-consumed tokens
unsigned int TokenBuffer::entries() const
{
        return queue.entries() - markerOffset;
}
 
#ifdef ANTLR_CXX_SUPPORTS_NAMESPACE
        }
#endif