persistence.antlr.InputBuffer Maven / Gradle / Ivy
package persistence.antlr;
/* ANTLR Translator Generator
* Project led by Terence Parr at http://www.jGuru.com
* Software rights: http://www.antlr.org/license.html
*
*/
// SAS: Added this class to genericise the input buffers for scanners
// This allows a scanner to use a binary (FileInputStream) or
// text (FileReader) stream of data; the generated scanner
// subclass will define the input stream
// There are two subclasses to this: CharBuffer and ByteBuffer
import java.io.IOException;
/**A Stream of characters fed to the lexer from a InputStream that can
* be rewound via mark()/rewind() methods.
*
* A dynamic array is used to buffer up all the input characters. Normally,
* "k" characters are stored in the buffer. More characters may be stored during
* guess mode (testing syntactic predicate), or when LT(i>k) is referenced.
* Consumption of characters is deferred. In other words, reading the next
* character is not done by conume(), but deferred until needed by LA or LT.
*
*
* @see persistence.antlr.CharQueue
*/
public abstract class InputBuffer {
// Number of active markers
protected int nMarkers = 0;
// Additional offset used when markers are active
protected int markerOffset = 0;
// Number of calls to consume() since last LA() or LT() call
protected int numToConsume = 0;
// Circular queue
protected CharQueue queue;
/** Create an input buffer */
public InputBuffer() {
queue = new CharQueue(1);
}
/** This method updates the state of the input buffer so that
* the text matched since the most recent mark() is no longer
* held by the buffer. So, you either do a mark/rewind for
* failed predicate or mark/commit to keep on parsing without
* rewinding the input.
*/
public void commit() {
nMarkers--;
}
/** Mark another character for deferred consumption */
public void consume() {
numToConsume++;
}
/** Ensure that the input buffer is sufficiently full */
public abstract void fill(int amount) throws CharStreamException;
public String getLAChars() {
StringBuffer la = new StringBuffer();
for (int i = markerOffset; i < queue.nbrEntries; i++)
la.append(queue.elementAt(i));
return la.toString();
}
public String getMarkedChars() {
StringBuffer marked = new StringBuffer();
for (int i = 0; i < markerOffset; i++)
marked.append(queue.elementAt(i));
return marked.toString();
}
public boolean isMarked() {
return (nMarkers != 0);
}
/** Get a lookahead character */
public char LA(int i) throws CharStreamException {
fill(i);
return queue.elementAt(markerOffset + i - 1);
}
/**Return an integer marker that can be used to rewind the buffer to
* its current state.
*/
public int mark() {
syncConsume();
nMarkers++;
return markerOffset;
}
/**Rewind the character buffer to a marker.
* @param mark Marker returned previously from mark()
*/
public void rewind(int mark) {
syncConsume();
markerOffset = mark;
nMarkers--;
}
/** Reset the input buffer
*/
public void reset() {
nMarkers = 0;
markerOffset = 0;
numToConsume = 0;
queue.reset();
}
/** Sync up deferred consumption */
protected void syncConsume() {
while (numToConsume > 0) {
if (nMarkers > 0) {
// guess mode -- leave leading characters and bump offset.
markerOffset++;
}
else {
// normal mode -- remove first character
queue.removeFirst();
}
numToConsume--;
}
}
}