1 /* 2 [The "BSD licence"] 3 Copyright (c) 2005-2008 Terence Parr 4 All rights reserved. 5 6 Redistribution and use in source and binary forms, with or without 7 modification, are permitted provided that the following conditions 8 are met: 9 1. Redistributions of source code must retain the above copyright 10 notice, this list of conditions and the following disclaimer. 11 2. Redistributions in binary form must reproduce the above copyright 12 notice, this list of conditions and the following disclaimer in the 13 documentation and/or other materials provided with the distribution. 14 3. The name of the author may not be used to endorse or promote products 15 derived from this software without specific prior written permission. 16 17 THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 18 IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 19 OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 20 IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 21 INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 22 NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23 DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24 THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 26 THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27 */ 28 package org.antlr.runtime.misc; 29 30 import java.util.List; 31 import java.util.ArrayList; 32 33 /** A lookahead queue that knows how to mark/release locations 34 * in the buffer for backtracking purposes. Any markers force the FastQueue 35 * superclass to keep all tokens until no more markers; then can reset 36 * to avoid growing a huge buffer. 37 */ 38 public abstract class LookaheadStream<T> extends FastQueue<T> { 39 public static final int UNINITIALIZED_EOF_ELEMENT_INDEX = Integer.MAX_VALUE; 40 41 /** Set to buffer index of eof when nextElement returns eof */ 42 protected int eofElementIndex = UNINITIALIZED_EOF_ELEMENT_INDEX; 43 44 /** Returned by nextElement upon end of stream; we add to buffer also */ 45 public T eof = null; 46 47 /** Track the last mark() call result value for use in rewind(). */ 48 protected int lastMarker; 49 50 /** tracks how deep mark() calls are nested */ 51 protected int markDepth = 0; 52 LookaheadStream(T eof)53 public LookaheadStream(T eof) { 54 this.eof = eof; 55 } 56 reset()57 public void reset() { 58 eofElementIndex = UNINITIALIZED_EOF_ELEMENT_INDEX; 59 super.reset(); 60 } 61 62 /** Implement nextElement to supply a stream of elements to this 63 * lookahead buffer. Return eof upon end of the stream we're pulling from. 64 */ 65 public abstract T nextElement(); 66 67 /** Get and remove first element in queue; override FastQueue.remove() */ remove()68 public T remove() { 69 T o = get(0); 70 p++; 71 // have we hit end of buffer and not backtracking? 72 if ( p == data.size() && markDepth==0 ) { 73 // if so, it's an opportunity to start filling at index 0 again 74 clear(); // size goes to 0, but retains memory 75 } 76 return o; 77 } 78 79 /** Make sure we have at least one element to remove, even if EOF */ consume()80 public void consume() { sync(1); remove(); } 81 82 /** Make sure we have 'need' elements from current position p. Last valid 83 * p index is data.size()-1. p+need-1 is the data index 'need' elements 84 * ahead. If we need 1 element, (p+1-1)==p must be < data.size(). 85 */ sync(int need)86 public void sync(int need) { 87 int n = (p+need-1) - data.size() + 1; // how many more elements we need? 88 if ( n > 0 ) fill(n); // out of elements? 89 } 90 91 /** add n elements to buffer */ fill(int n)92 public void fill(int n) { 93 for (int i=1; i<=n; i++) { 94 T o = nextElement(); 95 if ( o==eof ) { 96 data.add(eof); 97 eofElementIndex = data.size()-1; 98 } 99 else data.add(o); 100 } 101 } 102 103 //public boolean hasNext() { return eofElementIndex!=UNINITIALIZED_EOF_ELEMENT_INDEX; } 104 105 /** Size of entire stream is unknown; we only know buffer size from FastQueue */ size()106 public int size() { throw new UnsupportedOperationException("streams are of unknown size"); } 107 LT(int k)108 public Object LT(int k) { 109 if ( k==0 ) { 110 return null; 111 } 112 if ( k<0 ) { 113 return LB(-k); 114 } 115 //System.out.print("LT(p="+p+","+k+")="); 116 if ( (p+k-1) >= eofElementIndex ) { // move to super.LT 117 return eof; 118 } 119 sync(k); 120 return get(k-1); 121 } 122 123 /** Look backwards k nodes */ LB(int k)124 protected Object LB(int k) { 125 if ( k==0 ) { 126 return null; 127 } 128 if ( (p-k)<0 ) { 129 return null; 130 } 131 return get(-k); 132 } 133 getCurrentSymbol()134 public Object getCurrentSymbol() { return LT(1); } 135 index()136 public int index() { return p; } 137 mark()138 public int mark() { 139 markDepth++; 140 lastMarker = index(); 141 return lastMarker; 142 } 143 release(int marker)144 public void release(int marker) { 145 // no resources to release 146 } 147 rewind(int marker)148 public void rewind(int marker) { 149 markDepth--; 150 seek(marker); // assume marker is top 151 // release(marker); // waste of call; it does nothing in this class 152 } 153 rewind()154 public void rewind() { 155 seek(lastMarker); // rewind but do not release marker 156 } 157 158 /** Seek to a 0-indexed position within data buffer. Can't handle 159 * case where you seek beyond end of existing buffer. Normally used 160 * to seek backwards in the buffer. Does not force loading of nodes. 161 */ seek(int index)162 public void seek(int index) { p = index; } 163 }