dfa.java

ANTLR(ANother Tool for Language Recognition)它是这样的一种工具

package org.antlr.runtime;

/** A DFA implemented as a set of transition tables.
 *
 *  Any state that has a semantic predicate edge is special; those states
 *  are generated with if-then-else structures in a specialStateTransition()
 *  which is generated by cyclicDFA template.
 *
 *  There are at most 32767 states (16-bit signed short).
 *  Could get away with byte sometimes but would have to generate different
 *  types and the simulation code too.  For a point of reference, the Java
 *  lexer's Tokens rule DFA has 326 states roughly.
 */
public class DFA {
	protected short[] eot;
	protected short[] eof;
	protected char[] min;
    protected char[] max;
    protected short[] accept;
    protected short[] special;
    protected short[][] transition;

	protected int decisionNumber;

	/** Which recognizer encloses this DFA?  Needed to check backtracking */
	protected BaseRecognizer recognizer;

	public static final boolean debug = false;

	/** From the input stream, predict what alternative will succeed
	 *  using this DFA (representing the covering regular approximation
	 *  to the underlying CFL).  Return an alternative number 1..n.  Throw
	 *  an exception upon error.
	 */
	public int predict(IntStream input)
		throws RecognitionException
	{
		int mark = input.mark();
		int s = 0; // we always start at s0
		try {
			while ( true ) {
				if ( debug ) System.err.println("DFA "+decisionNumber+" state "+s+" LA(1)="+(char)input.LA(1)+"("+input.LA(1)+")");
				int specialState = special[s];
				if ( specialState>=0 ) {
					if ( debug ) System.err.println("DFA "+decisionNumber+
						" state "+s+" is special state "+specialState);
					s = specialStateTransition(specialState);
					input.consume();
					continue;
				}
				if ( accept[s] >= 1 ) {
					if ( debug ) System.err.println("accept; predict "+accept[s]+" from state "+s);
					return accept[s];
				}
				// look for a normal char transition
				char c = (char)input.LA(1); // -1 == \uFFFF, all tokens fit in 65000 space
				if (c>=min[s] && c<=max[s]) {
					int snext = transition[s][c-min[s]]; // move to next state
					if ( snext < 0 ) {
						// was in range but not a normal transition
						// must check EOT, which is like the else clause.
						// eot[s]>=0 indicates that an EOT edge goes to another
						// state.
						if ( eot[s]>=0 ) {  // EOT Transition to accept state?
							if ( debug ) System.err.println("EOT transition");
							s = eot[s];
							input.consume();
							// TODO: I had this as return accept[eot[s]]
							// which assumed here that the EOT edge always
							// went to an accept...faster to do this, but
							// what about predicated edges coming from EOT
							// target?
							continue;
						}
						noViableAlt(s,input);
						return 0;
					}
					s = snext;
					input.consume();
					continue;
				}
				if ( eot[s]>=0 ) {  // EOT Transition?
					if ( debug ) System.err.println("EOT transition");
					s = eot[s];
					input.consume();
					continue;
				}
				if ( c==(char)Token.EOF && eof[s]>=0 ) {  // EOF Transition to accept state?
					if ( debug ) System.err.println("accept via EOF; predict "+accept[eof[s]]+" from "+eof[s]);
					return accept[eof[s]];
				}
				// not in range and not EOF/EOT, must be invalid symbol
				if ( debug ) {
					System.err.println("min["+s+"]="+min[s]);
					System.err.println("max["+s+"]="+max[s]);
					System.err.println("eot["+s+"]="+eot[s]);
					System.err.println("eof["+s+"]="+eof[s]);
					for (int p=0; p<transition[s].length; p++) {
						System.err.print(transition[s][p]+" ");
					}
					System.err.println();
				}
				noViableAlt(s,input);
				return 0;
			}
		}
		finally {
			input.rewind(mark);
		}
	}

	protected void noViableAlt(int s, IntStream input) throws NoViableAltException {
		if (recognizer.backtracking>0) {
			recognizer.failed=true;
			return;
		}
		NoViableAltException nvae =
			new NoViableAltException(getDescription(),
									 decisionNumber,
									 s,
									 input);
		error(nvae);
		throw nvae;
	}

	/** A hook for debugging interface */
	protected void error(NoViableAltException nvae) { ; }

	public int specialStateTransition(int s) throws NoViableAltException {
		return -1;
	}

	public String getDescription() {
		return "n/a";
	}

	/** Given a String that has a run-length-encoding of some unsigned shorts
	 *  like "\1\2\3\9", convert to short[] {2,9,9,9}.  We do this to avoid
	 *  static short[] which generates so much init code that the class won't
	 *  compile. :(
	 */
	public static short[] unpackEncodedString(String encodedString) {
		// walk first to find how big it is.
		int size = 0;
		for (int i=0; i<encodedString.length(); i+=2) {
			size += encodedString.charAt(i);
		}
		short[] data = new short[size];
		int di = 0;
		for (int i=0; i<encodedString.length(); i+=2) {
			char n = encodedString.charAt(i);
			char v = encodedString.charAt(i+1);
			// add v n times to data
			for (int j=1; j<=n; j++) {
				data[di++] = (short)v;
			}
		}
		return data;
	}

	/** Hideous duplication of code, but I need different typed arrays out :( */
	public static char[] unpackEncodedStringToUnsignedChars(String encodedString) {
		// walk first to find how big it is.
		int size = 0;
		for (int i=0; i<encodedString.length(); i+=2) {
			size += encodedString.charAt(i);
		}
		char[] data = new char[size];
		int di = 0;
		for (int i=0; i<encodedString.length(); i+=2) {
			char n = encodedString.charAt(i);
			char v = encodedString.charAt(i+1);
			// add v n times to data
			for (int j=1; j<=n; j++) {
				data[di++] = v;
			}
		}
		return data;
	}

	public int specialTransition(int state, int symbol) {
		return 0;
	}
}