bitstreamhpindexreader.c

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				positionsToReadToReachCurrentPosition += count;
				if ( COOKIES ) positionsToReadToReachCurrentPosition++;
			}
			count = -1;
			positionsUnread = true;
			return currentDocument;
		}

		/**
		 * Reads the entire skip tower for the current position. This method assumes that the tower
		 * has been passed over sequentially, and correpondingly sets {@link #lastPositionsIncrement}
		 * to the number of positions bits of the last quantum.
		 */
		private void readTower() throws IOException {
			lastPositionsIncrement = maxh >= 0 ? positionsBitSkip[ 0 ] : 0;
			if ( DEBUG ) System.err.println( this + ": Setting lastPositionsIncrement to " + lastPositionsIncrement + " in readTower()" );
			readTower( -1 );
			if ( DEBUG ) System.err.println( this + ": Incrementing positionsBitsOffset by " + lastPositionsIncrement + " in readTower()" );
			// TODO: this should be moved into readTower(int)
			positionsBitsOffset += lastPositionsIncrement;
		}

		/**
		 * Reads the skip tower for the current position, possibly skipping part of the tower.
		 * 
		 * <P>Note that this method will update {@link #state} only if it reads the entire tower,
		 * otherwise the state remains {@link #BEFORE_TOWER}.
		 * 
		 * @param pointer the tower will be read up to the first entry smaller than or equal to this
		 * pointer; use -1 to guarantee that the entire tower will be read.
		 */
		private void readTower( final int pointer ) throws IOException {
			int i, j, k, cacheOffset, cache, towerLength = 0;
			long bitsAtTowerStart = 0;
			boolean truncated = false;
			if ( ASSERTS ) assert numberOfDocumentRecord % quantum == 0;
			if ( ASSERTS && state != BEFORE_TOWER ) throw new IllegalStateException( "readTower() called in state " + state );
			cacheOffset = ( numberOfDocumentRecord & wModuloMask );
			k = cacheOffset >> quantumDivisionShift;
			if ( ASSERTS && k == 0 ) { // Invalidate current tower data
				it.unimi.dsi.fastutil.ints.IntArrays.fill( pointerSkip, Integer.MAX_VALUE );
				it.unimi.dsi.fastutil.longs.LongArrays.fill( bitSkip, Integer.MAX_VALUE );
				it.unimi.dsi.fastutil.longs.LongArrays.fill( positionsBitSkip, Integer.MAX_VALUE );
			}
			// Compute the height of the current skip tower.
			s = ( k == 0 ) ? height : Fast.leastSignificantBit( k );
			cache = frequency - w * ( numberOfDocumentRecord >> wDivisionShift );
			if ( cache < w ) {
				maxh = Fast.mostSignificantBit( ( cache >> quantumDivisionShift ) - k );
				if ( maxh < s ) {
					s = maxh;
					truncated = true;
				}
				else truncated = false;
			}
			else {
				cache = w;
				maxh = height;
				truncated = k == 0;
			}
			// assert w == cache || k == 0 || lastMaxh == Fast.mostSignificantBit( k ^ (
			// cache/quantum ) ) : lastMaxh +","+ (Fast.mostSignificantBit( k ^ ( cache/quantum )
			// ));
			i = s;
			if ( s >= 0 ) {
				if ( k == 0 ) {
					if ( quantumBitLength < 0 ) {
						quantumBitLength = ibs.readDelta();
						positionsQuantumBitLength = ibs.readDelta();
						entryBitLength = ibs.readDelta();
					}
					else {
						quantumBitLength += Fast.nat2int( ibs.readDelta() );
						positionsQuantumBitLength += Fast.nat2int( ibs.readDelta() );
						entryBitLength += Fast.nat2int( ibs.readDelta() );
					}
					if ( DEBUG ) System.err.println( "{" + this + "} quantum bit length=" + quantumBitLength + " positions quantum bit length=" + positionsQuantumBitLength + " entry bit length=" + entryBitLength );
				}
				if ( DEBUG ) System.err.println( "{" + this + "} Reading tower; pointer=" + pointer + " maxh=" + maxh + " s=" + s );
				if ( s > 0 ) {
					towerLength = entryBitLength * ( s + 1 ) + Fast.nat2int( ibs.readDelta() );
					if ( DEBUG ) System.err.println( "{" + this + "} Tower length=" + towerLength );
				}
				// We store the number of bits read at the start of the tower (just after the
				// length).
				bitsAtTowerStart = ibs.readBits();
				if ( truncated ) {
					if ( DEBUG ) System.err.println( "{" + this + "} Truncated--reading tops" );
					// We read the tower top.
					pointerSkip[ s ] = Fast.nat2int( ibs.readGolomb( towerTopB[ s ], towerTopLog2B[ s ] ) ) + pointerPrediction[ s ];
					bitSkip[ s ] = quantumBitLength * ( 1 << s ) + entryBitLength * ( ( 1 << s + 1 ) - s - 2 ) + Fast.nat2int( ibs.readLongDelta() );
					positionsBitSkip[ s ] = positionsQuantumBitLength * ( 1 << s ) + Fast.nat2int( ibs.readLongDelta() );
				}
				else {
					// We copy the tower top from the lowest inherited entry suitably updated.
					pointerSkip[ s ] = pointerSkip[ s + 1 ] - ( currentDocument - pointerAtLastSkipTower );
					bitSkip[ s ] = bitSkip[ s + 1 ] - ( bitsAtTowerStart - readBitsAtLastSkipTower ) - towerLength;
					// TODO: note that we could use the same method for pointers and bit skips!
					positionsBitSkip[ s ] = positionsBitSkip[ s + 1 ] - positionsBitSkip[ s ];
					if ( ASSERTS ) assert positionsBitSkip[ s ] > 0 : positionsBitSkip[ s ] + " <= " + 0;
				}
				// We read the remaining part of the tower, at least until we point after pointer.
				if ( currentDocument + pointerSkip[ i ] > pointer ) {
					for ( i = s - 1; i >= 0; i-- ) {
						pointerSkip[ i ] = Fast.nat2int( ibs.readGolomb( towerLowerB[ i ], towerLowerLog2B[ i ] ) ) + pointerSkip[ i + 1 ] / 2;
						bitSkip[ i ] = ( bitSkip[ i + 1 ] - entryBitLength * ( i + 1 ) ) / 2 - Fast.nat2int( ibs.readLongDelta() );
						positionsBitSkip[ i ] = positionsBitSkip[ i + 1 ] / 2 - Fast.nat2int( ibs.readLongDelta() );
						if ( DEBUG && currentDocument + pointerSkip[ i ] <= pointer ) System.err.println( "{" + this + "} stopping reading at i=" + i + " as currentDocument (" + currentDocument
								+ ") plus pointer skip (" + pointerSkip[ i ] + ") is smaller than or equal target (" + pointer + ")" );
						if ( currentDocument + pointerSkip[ i ] <= pointer ) break;
					}
				}
			}
			/*
			 * If we did not read the entire tower, we need to fix the skips we read (as they are
			 * offsets from the *end* of the tower) and moreover we must make unusable the rest of
			 * the tower (for asserts).
			 */
			if ( i > 0 ) {
				final long fix = ibs.readBits() - bitsAtTowerStart;
				for ( j = s; j >= i; j-- )
					bitSkip[ j ] += towerLength - fix;
				if ( ASSERTS ) for ( ; j >= 0; j-- )
					pointerSkip[ j ] = Integer.MAX_VALUE;
			}
			else state = BEFORE_COUNT;
			// We update the inherited tower.
			final long deltaBits = ibs.readBits() - readBitsAtLastSkipTower;
			final int deltaPointers = currentDocument - pointerAtLastSkipTower;

			if ( ASSERTS ) assert lastPositionsIncrement >= 0 : lastPositionsIncrement + " < " + 0;

			for ( j = Fast.mostSignificantBit( k ^ ( cache >> quantumDivisionShift ) ); j >= s + 1; j-- ) {
				bitSkip[ j ] -= deltaBits;
				positionsBitSkip[ j ] -= lastPositionsIncrement;
				pointerSkip[ j ] -= deltaPointers;
			}

			readBitsAtLastSkipTower = ibs.readBits();
			pointerAtLastSkipTower = currentDocument;
			lowest = i < 0 ? 0 : i;

			if ( DEBUG ) {
				System.err.println( "{" + this + "} " + "Computed skip tower (lowest: " + lowest + ") for document record number " + numberOfDocumentRecord + " (pointer " + currentDocument + ") from " + Math.max( i, 0 ) + ": " );
				System.err.print( "% " );
				for ( j = 0; j <= s; j++ )
					System.err.print( pointerSkip[ j ] + ":" + bitSkip[ j ] + ":" + positionsBitSkip[ j ] + " " );
				System.err.print( " [" );
				for ( ; j <= height; j++ )
					System.err.print( pointerSkip[ j ] + ":" + bitSkip[ j ] + ":" + positionsBitSkip[ j ] + " " );
				System.err.print( "]" );
				System.err.println();
			}

			if ( ASSERTS ) {
				for ( j = Fast.mostSignificantBit( k ^ ( cache >> quantumDivisionShift ) ); j >= s + 1; j-- ) {
					assert positionsBitSkip[ j ] >= 0 : "positionsBitSkip[" + j + "] = " + positionsBitSkip[ j ]  + " < " + 0;
					assert positionsBitSkip[ j ] >= positionsBitSkip[ j - 1 ] : 
						"positionsBitSkip[" + j + "] = " + positionsBitSkip[ j ]  + " < " + positionsBitSkip[ j - 1 ] + " = positionsBitSkip[" + ( j - 1 ) + "]";
				}
			}

		}


		public int skipTo( final int p ) throws IOException {
			if ( DEBUG ) System.err.println( this + ".skipTo(" + p + ") [currentDocument=" + currentDocument + ", numberOfDocumentRecord=" + numberOfDocumentRecord + ", positionsBitsOffset=" + positionsBitsOffset + "]" );
			// If we are just at the start of a list, let us read the first pointer.
			if ( numberOfDocumentRecord == -1 ) nextDocument(); // TODO: shouldn't we just read the
																// tower?
			if ( currentDocument >= p ) {
				if ( DEBUG ) System.err.println( this + ": No skip necessary, returning " + currentDocument );
				return currentDocument;
			}
			if ( state == BEFORE_TOWER ) {
				lastPositionsIncrement = maxh >= 0 ? positionsBitSkip[ 0 ] : 0;
				readTower( p );
				if ( DEBUG ) System.err.println( this + ": Incrementing positionsBitsOffset by " + lastPositionsIncrement + " in skipTo() initial phase" );
				positionsBitsOffset += lastPositionsIncrement;
			}

			final int[] pointerSkip = this.pointerSkip;
			for ( ;; ) {
				if ( ASSERTS ) assert maxh < 0 || lowest > 0 || pointerSkip[ 0 ] != Integer.MAX_VALUE;
				// If on a defective quantum (no tower) or p is inside the current quantum (no
				// need to scan the tower) we bail out.
				if ( maxh < 0 || lowest == 0 && pointerAtLastSkipTower + pointerSkip[ 0 ] > p ) break;
				if ( DEBUG ) System.err.println( this + ": In for loop, currentDocument=" + currentDocument + ", maxh=" + maxh + ", numberOfDocumentRecord=" + numberOfDocumentRecord + ", p=" + p );
				final int cacheOffset = ( numberOfDocumentRecord & wModuloMask );
				final int k = cacheOffset >> quantumDivisionShift;
				final int top = Fast.mostSignificantBit( k ^ ( Math.min( w, frequency - numberOfDocumentRecord + cacheOffset ) >> quantumDivisionShift ) );
				int i;
				for ( i = lowest; i <= top; i++ ) {
					if ( ASSERTS && ( k & 1 << i ) != 0 ) assert pointerSkip[ i ] == pointerSkip[ i + 1 ];
					if ( ASSERTS ) assert pointerSkip[ i ] != Integer.MAX_VALUE : "Invalid pointer skip " + i + " (lowest=" + lowest + ", top=" + top + ")";
					if ( pointerAtLastSkipTower + pointerSkip[ i ] > p ) break;
				}
				if ( --i < 0 ) break;
				if ( ASSERTS ) assert i >= lowest : i + " < " + lowest;
				if ( DEBUG ) System.err.println( this + ": Safely after for with i=" + i + ", P[i]=" + pointerSkip[ i ] + ", A[i]=" + bitSkip[ i ] + ", B[i]=" + positionsBitSkip[ i ] );
				if ( DEBUG ) System.err.println( this + ": [" + ibs.readBits() + "] Skipping " + ( bitSkip[ i ] - ( ibs.readBits() - readBitsAtLastSkipTower ) ) + " bits ("
						+ ( ( ( k & -( 1 << i ) ) + ( 1 << i ) ) * quantum - cacheOffset ) + " records) to get to document pointer " + ( currentDocument + pointerSkip[ i ] ) );
				ibs.skip( bitSkip[ i ] - ( ibs.readBits() - readBitsAtLastSkipTower ) );
				/* We accumulate the number of bits that must be skipped in the positions stream to reach the position
				 * corresponding to the current tower. */
				if ( DEBUG ) System.err.println( this + ": Incrementing positionsBitsOffset by " + positionsBitSkip[ i ] + " (height " + i + ")" );
				lastPositionsIncrement = positionsBitSkip[ i ];
				positionsBitsOffset += lastPositionsIncrement;
				if ( ASSERTS && positionsLength != -1 ) assert positionsBitsOffset <= positionsLength : positionsBitsOffset + " > " + positionsLength;
				state = BEFORE_TOWER;
				currentDocument = pointerSkip[ i ] + pointerAtLastSkipTower;
				numberOfDocumentRecord += ( ( k & -( 1 << i ) ) + ( 1 << i ) ) * quantum - cacheOffset;
				// If we skipped beyond the end of the list, we invalidate the current document.
				if ( numberOfDocumentRecord == frequency ) {
					currentDocument = Integer.MAX_VALUE;
					positionsUnread = false;
					state = BEFORE_POINTER; // We are actually before a frequency, but we must
					// avoid that calls to nextDocument() read anything
				}
				else {
					positionsUnread = true;
					readTower( p ); // Note that if we are exactly on the destination pointer, we will read the entire tower.
				}

				count = -1; // We must invalidate count as readDocumentPointer() would do.
				positionsToReadToReachCurrentPosition = 0;
				if ( endOfList() ) {
					if ( DEBUG ) System.err.println( this + ".toSkip(): end-of-list, returning " + currentDocument + ", state=" + state );
					// Note that if p == Integer.MAX_VALUE, we are certainly beyond end-of-list
					return p == Integer.MAX_VALUE ? Integer.MAX_VALUE : currentDocument;
				}
			}
			if ( DEBUG ) System.err.println( this + ": Completing sequentially, currentDocument=" + currentDocument + ", numberOfDocumentRecord=" + numberOfDocumentRecord + ", p=" + p );
			while ( currentDocument < p ) {
				if ( DEBUG ) System.err.println( this + ": Skipping sequentially (second), currentDocument=" + currentDocument + ", numberOfDocumentRecord=" + numberOfDocumentRecord + ", p=" + p );
				if ( nextDocument() == -1 ) {
					if ( DEBUG ) System.err.println( this + ": end-of-list, returning MAX_VALUE" );
					return Integer.MAX_VALUE;
				}
			}
			if ( DEBUG ) System.err.println( this + ".toSkip(): Returning " + currentDocument );
			return currentDocument;
		}

		public void dispose() throws IOException {
			parent.close();
		}

		public boolean hasNext() {
			return !endOfList();
		}

		public int nextInt() {
			if ( !hasNext() ) throw new NoSuchElementException();
			try {
				return nextDocument();
			}
			catch ( IOException e ) {
				throw new RuntimeException( e );
			}
		}

		public String toString() {
			return index + " [" + term + "]";
		}

		/**
		 * An interval iterator returning the positions of the current document as singleton
		 * intervals.
		 */
		private final class IndexIntervalIterator extends AbstractObjectIterator<Interval> implements IntervalIterator {
			int pos = -1;

			public void reset() throws IOException {
				pos = -1;
				if ( positionsUnread ) updatePositionCache(); // This guarantees the position cache is ok
			}

			public void intervalTerms( final IntSet terms ) {
				terms.add( BitStreamHPIndexReaderIndexIterator.this.term );
			}

			public boolean hasNext() {
				return pos < count - 1;
			}

			public Interval next() {
				if ( !hasNext() ) throw new NoSuchElementException();
				return Interval.valueOf( positionCache[ ++pos ] );
			}

			public Interval nextInterval() {
				return pos < count - 1 ? Interval.valueOf( positionCache[ ++pos ] ) : null;
			}

			public int extent() {
				return 1;
			}

			public String toString() {
				return index + ": " + term + "[doc=" + currentDocument + ", count=" + count + ", pos=" + pos + "]";
			}
		};

		public Reference2ReferenceMap<Index, IntervalIterator> intervalIterators() throws IOException {
			intervalIterator();
			return singletonIntervalIterator;
		}

		public IntervalIterator intervalIterator() throws IOException {
			return intervalIterator( keyIndex );
		}

		public IntervalIterator intervalIterator( final Index index ) throws IOException {
			if ( ASSERTS ) ensureCurrentDocument();
			// TODO: this was if ( index != keyIndex || hasPayloads )
			if ( index != keyIndex ) return IntervalIterators.TRUE;
			if ( ASSERTS ) assert intervalIterator != null;
			intervalIterator.reset();
			return intervalIterator;
		}

		public ReferenceSet<Index> indices() {
			return index.singletonSet;
		}
	}

	private IndexIterator documents( final CharSequence term, final int termNumber ) throws IOException {
		indexIterator.term( term );
		indexIterator.position( termNumber );
		return indexIterator;
	}

	public IndexIterator documents( final int term ) throws IOException {
		return documents( null, term );
	}

	public IndexIterator documents( final CharSequence term ) throws IOException {
		if ( closed ) throw new IllegalStateException( "This " + getClass().getSimpleName() + " has been closed" );
		if ( index.termMap != null ) {
			final int termIndex = (int)index.termMap.getLong( term );
			if ( termIndex == -1 ) return index.emptyIndexIterator;
			return documents( term, termIndex );
		}
		throw new UnsupportedOperationException( "Index " + index + " has no term map" );
	}

	@Override
	public IndexIterator nextIterator() throws IOException {
		return indexIterator.advance();
	}

	public String toString() {
		return getClass().getSimpleName() + "[" + index + "]";
	}
	
	public void close() throws IOException {
		super.close();
		indexIterator.ibs.close();
		indexIterator.positions.close();
	}
}

#else
"Mismatch in specified directives. First of all, you must define CLASSNAME."
"Then, you must either just define GENERIC, or the full range of assertions"
"(#frequencies, #pointers, #counts, #positions)."
#endif