lucene/core/src/java/org/apache/lucene/store/BufferedIndexInput.java - lucene-solr - Git at Google

 /*
  * Licensed to the Apache Software Foundation (ASF) under one or more
  * contributor license agreements.  See the NOTICE file distributed with
  * this work for additional information regarding copyright ownership.
  * The ASF licenses this file to You under the Apache License, Version 2.0
  * (the "License"); you may not use this file except in compliance with
  * the License.  You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 package org.apache.lucene.store;


 import java.io.EOFException;
 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;

 /** Base implementation class for buffered {@link IndexInput}. */
 public abstract class BufferedIndexInput extends IndexInput implements RandomAccessInput {

   private static final ByteBuffer EMPTY_BYTEBUFFER = ByteBuffer.allocate(0);

   /** Default buffer size set to {@value #BUFFER_SIZE}. */
   public static final int BUFFER_SIZE = 1024;

   /** Minimum buffer size allowed */
   public static final int MIN_BUFFER_SIZE = 8;

   // The normal read buffer size defaults to 1024, but
   // increasing this during merging seems to yield
   // performance gains.  However we don't want to increase
   // it too much because there are quite a few
   // BufferedIndexInputs created during merging.  See
   // LUCENE-888 for details.
   /**
    * A buffer size for merges set to {@value #MERGE_BUFFER_SIZE}.
    */
   public static final int MERGE_BUFFER_SIZE = 4096;

   private int bufferSize = BUFFER_SIZE;

   private ByteBuffer buffer = EMPTY_BYTEBUFFER;

   private long bufferStart = 0;       // position in file of buffer

   @Override
   public final byte readByte() throws IOException {
     if (buffer.hasRemaining() == false) {
       refill();
     }
     return buffer.get();
   }

   public BufferedIndexInput(String resourceDesc) {
     this(resourceDesc, BUFFER_SIZE);
   }

   public BufferedIndexInput(String resourceDesc, IOContext context) {
     this(resourceDesc, bufferSize(context));
   }

   /** Inits BufferedIndexInput with a specific bufferSize */
   public BufferedIndexInput(String resourceDesc, int bufferSize) {
     super(resourceDesc);
     checkBufferSize(bufferSize);
     this.bufferSize = bufferSize;
   }

   /** Change the buffer size used by this IndexInput */
   public final void setBufferSize(int newSize) {
     assert buffer == EMPTY_BYTEBUFFER || bufferSize == buffer.capacity(): "buffer=" + buffer + " bufferSize=" + bufferSize + " buffer.length=" + (buffer != null ? buffer.capacity() : 0);
     if (newSize != bufferSize) {
       checkBufferSize(newSize);
       bufferSize = newSize;
       if (buffer != EMPTY_BYTEBUFFER) {
         // Resize the existing buffer and carefully save as
         // many bytes as possible starting from the current
         // bufferPosition
         ByteBuffer newBuffer = ByteBuffer.allocate(newSize);
         assert newBuffer.order() == ByteOrder.BIG_ENDIAN;
         if (buffer.remaining() > newBuffer.capacity()) {
           buffer.limit(buffer.position() + newBuffer.capacity());
         }
         assert buffer.remaining() <= newBuffer.capacity();
         newBuffer.put(buffer);
         newBuffer.flip();
         buffer = newBuffer;
       }
     }
   }

   /** Returns buffer size.  @see #setBufferSize */
   public final int getBufferSize() {
     return bufferSize;
   }

   private void checkBufferSize(int bufferSize) {
     if (bufferSize < MIN_BUFFER_SIZE)
       throw new IllegalArgumentException("bufferSize must be at least MIN_BUFFER_SIZE (got " + bufferSize + ")");
   }

   @Override
   public final void readBytes(byte[] b, int offset, int len) throws IOException {
     readBytes(b, offset, len, true);
   }

   @Override
   public final void readBytes(byte[] b, int offset, int len, boolean useBuffer) throws IOException {
     int available = buffer.remaining();
     if(len <= available){
       // the buffer contains enough data to satisfy this request
       if(len>0) // to allow b to be null if len is 0...
         buffer.get(b, offset, len);
     } else {
       // the buffer does not have enough data. First serve all we've got.
       if(available > 0){
         buffer.get(b, offset, available);
         offset += available;
         len -= available;
       }
       // and now, read the remaining 'len' bytes:
       if (useBuffer && len<bufferSize){
         // If the amount left to read is small enough, and
         // we are allowed to use our buffer, do it in the usual
         // buffered way: fill the buffer and copy from it:
         refill();
         if(buffer.remaining()<len){
           // Throw an exception when refill() could not read len bytes:
           buffer.get(b, offset, buffer.remaining());
           throw new EOFException("read past EOF: " + this);
         } else {
           buffer.get(b, offset, len);
         }
       } else {
         // The amount left to read is larger than the buffer
         // or we've been asked to not use our buffer -
         // there's no performance reason not to read it all
         // at once. Note that unlike the previous code of
         // this function, there is no need to do a seek
         // here, because there's no need to reread what we
         // had in the buffer.
         long after = bufferStart+buffer.position()+len;
         if(after > length())
           throw new EOFException("read past EOF: " + this);
         readInternal(ByteBuffer.wrap(b, offset, len));
         bufferStart = after;
         buffer.limit(0);  // trigger refill() on read
       }
     }
   }

   @Override
   public final short readShort() throws IOException {
     if (Short.BYTES <= buffer.remaining()) {
       return buffer.getShort();
     } else {
       return super.readShort();
     }
   }

   @Override
   public final int readInt() throws IOException {
     if (Integer.BYTES <= buffer.remaining()) {
       return buffer.getInt();
     } else {
       return super.readInt();
     }
   }

   @Override
   public final long readLong() throws IOException {
     if (Long.BYTES <= buffer.remaining()) {
       return buffer.getLong();
     } else {
       return super.readLong();
     }
   }

   @Override
   public final int readVInt() throws IOException {
     if (5 <= buffer.remaining()) {
       byte b = buffer.get();
       if (b >= 0) return b;
       int i = b & 0x7F;
       b = buffer.get();
       i |= (b & 0x7F) << 7;
       if (b >= 0) return i;
       b = buffer.get();
       i |= (b & 0x7F) << 14;
       if (b >= 0) return i;
       b = buffer.get();
       i |= (b & 0x7F) << 21;
       if (b >= 0) return i;
       b = buffer.get();
       // Warning: the next ands use 0x0F / 0xF0 - beware copy/paste errors:
       i |= (b & 0x0F) << 28;
       if ((b & 0xF0) == 0) return i;
       throw new IOException("Invalid vInt detected (too many bits)");
     } else {
       return super.readVInt();
     }
   }

   @Override
   public final long readVLong() throws IOException {
     if (9 <= buffer.remaining()) {
       byte b = buffer.get();
       if (b >= 0) return b;
       long i = b & 0x7FL;
       b = buffer.get();
       i |= (b & 0x7FL) << 7;
       if (b >= 0) return i;
       b = buffer.get();
       i |= (b & 0x7FL) << 14;
       if (b >= 0) return i;
       b = buffer.get();
       i |= (b & 0x7FL) << 21;
       if (b >= 0) return i;
       b = buffer.get();
       i |= (b & 0x7FL) << 28;
       if (b >= 0) return i;
       b = buffer.get();
       i |= (b & 0x7FL) << 35;
       if (b >= 0) return i;
       b = buffer.get();
       i |= (b & 0x7FL) << 42;
       if (b >= 0) return i;
       b = buffer.get();
       i |= (b & 0x7FL) << 49;
       if (b >= 0) return i;
       b = buffer.get();
       i |= (b & 0x7FL) << 56;
       if (b >= 0) return i;
       throw new IOException("Invalid vLong detected (negative values disallowed)");
     } else {
       return super.readVLong();
     }
   }

   @Override
   public final byte readByte(long pos) throws IOException {
     long index = pos - bufferStart;
     if (index < 0 || index >= buffer.limit()) {
       bufferStart = pos;
       buffer.limit(0);  // trigger refill() on read
       seekInternal(pos);
       refill();
       index = 0;
     }
     return buffer.get((int) index);
   }

   @Override
   public final short readShort(long pos) throws IOException {
     long index = pos - bufferStart;
     if (index < 0 || index >= buffer.limit()-1) {
       bufferStart = pos;
       buffer.limit(0);  // trigger refill() on read
       seekInternal(pos);
       refill();
       index = 0;
     }
     return buffer.getShort((int) index);
   }

   @Override
   public final int readInt(long pos) throws IOException {
     long index = pos - bufferStart;
     if (index < 0 || index >= buffer.limit()-3) {
       bufferStart = pos;
       buffer.limit(0);  // trigger refill() on read
       seekInternal(pos);
       refill();
       index = 0;
     }
     return buffer.getInt((int) index);
   }

   @Override
   public final long readLong(long pos) throws IOException {
     long index = pos - bufferStart;
     if (index < 0 || index >= buffer.limit()-7) {
       bufferStart = pos;
       buffer.limit(0);  // trigger refill() on read
       seekInternal(pos);
       refill();
       index = 0;
     }
     return buffer.getLong((int) index);
   }

   private void refill() throws IOException {
     long start = bufferStart + buffer.position();
     long end = start + bufferSize;
     if (end > length())  // don't read past EOF
       end = length();
     int newLength = (int)(end - start);
     if (newLength <= 0)
       throw new EOFException("read past EOF: " + this);

     if (buffer == EMPTY_BYTEBUFFER) {
       buffer = ByteBuffer.allocate(bufferSize);  // allocate buffer lazily
       seekInternal(bufferStart);
     }
     buffer.position(0);
     buffer.limit(newLength);
     bufferStart = start;
     readInternal(buffer);
     // Make sure sub classes don't mess up with the buffer.
     assert buffer.order() == ByteOrder.BIG_ENDIAN : buffer.order();
     assert buffer.remaining() == 0 : "should have thrown EOFException";
     assert buffer.position() == newLength;
     buffer.flip();
   }

   /** Expert: implements buffer refill.  Reads bytes from the current position
    * in the input.
    * @param b the buffer to read bytes into
    */
   protected abstract void readInternal(ByteBuffer b) throws IOException;

   @Override
   public final long getFilePointer() { return bufferStart + buffer.position(); }

   @Override
   public final void seek(long pos) throws IOException {
     if (pos >= bufferStart && pos < (bufferStart + buffer.limit()))
       buffer.position((int)(pos - bufferStart));  // seek within buffer
     else {
       bufferStart = pos;
       buffer.limit(0);  // trigger refill() on read
       seekInternal(pos);
     }
   }

   /** Expert: implements seek.  Sets current position in this file, where the
    * next {@link #readInternal(ByteBuffer)} will occur.
    * @see #readInternal(ByteBuffer)
    */
   protected abstract void seekInternal(long pos) throws IOException;

   @Override
   public BufferedIndexInput clone() {
     BufferedIndexInput clone = (BufferedIndexInput)super.clone();

     clone.buffer = EMPTY_BYTEBUFFER;
     clone.bufferStart = getFilePointer();

     return clone;
   }

   @Override
   public IndexInput slice(String sliceDescription, long offset, long length) throws IOException {
     return wrap(sliceDescription, this, offset, length);
   }

   /**
    * Returns default buffer sizes for the given {@link IOContext}
    */
   public static int bufferSize(IOContext context) {
     switch (context.context) {
     case MERGE:
       return MERGE_BUFFER_SIZE;
     default:
       return BUFFER_SIZE;
     }
   }

   /**
    * Wraps a portion of another IndexInput with buffering.
    * <p><b>Please note:</b> This is in most cases ineffective, because it may double buffer!
    */
   public static BufferedIndexInput wrap(String sliceDescription, IndexInput other, long offset, long length) {
     return new SlicedIndexInput(sliceDescription, other, offset, length);
   }

   /**
    * Implementation of an IndexInput that reads from a portion of a file.
    */
   private static final class SlicedIndexInput extends BufferedIndexInput {
     IndexInput base;
     long fileOffset;
     long length;

     SlicedIndexInput(String sliceDescription, IndexInput base, long offset, long length) {
       super((sliceDescription == null) ? base.toString() : (base.toString() + " [slice=" + sliceDescription + "]"), BufferedIndexInput.BUFFER_SIZE);
       if (offset < 0 || length < 0 || offset + length > base.length()) {
         throw new IllegalArgumentException("slice() " + sliceDescription + " out of bounds: "  + base);
       }
       this.base = base.clone();
       this.fileOffset = offset;
       this.length = length;
     }

     @Override
     public SlicedIndexInput clone() {
       SlicedIndexInput clone = (SlicedIndexInput)super.clone();
       clone.base = base.clone();
       clone.fileOffset = fileOffset;
       clone.length = length;
       return clone;
     }

     @Override
     protected void readInternal(ByteBuffer b) throws IOException {
       long start = getFilePointer();
       if (start + b.remaining() > length) {
         throw new EOFException("read past EOF: " + this);
       }
       base.seek(fileOffset + start);
       base.readBytes(b.array(), b.position(), b.remaining());
       b.position(b.position() + b.remaining());
     }

     @Override
     protected void seekInternal(long pos) {}

     @Override
     public void close() throws IOException {
       base.close();
     }

     @Override
     public long length() {
       return length;
     }
   }
 }
	/*
	* Licensed to the Apache Software Foundation (ASF) under one or more
	* contributor license agreements. See the NOTICE file distributed with
	* this work for additional information regarding copyright ownership.
	* The ASF licenses this file to You under the Apache License, Version 2.0
	* (the "License"); you may not use this file except in compliance with
	* the License. You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/
	package org.apache.lucene.store;


	import java.io.EOFException;
	import java.io.IOException;
	import java.nio.ByteBuffer;
	import java.nio.ByteOrder;

	/** Base implementation class for buffered {@link IndexInput}. */
	public abstract class BufferedIndexInput extends IndexInput implements RandomAccessInput {

	private static final ByteBuffer EMPTY_BYTEBUFFER = ByteBuffer.allocate(0);

	/** Default buffer size set to {@value #BUFFER_SIZE}. */
	public static final int BUFFER_SIZE = 1024;

	/** Minimum buffer size allowed */
	public static final int MIN_BUFFER_SIZE = 8;

	// The normal read buffer size defaults to 1024, but
	// increasing this during merging seems to yield
	// performance gains. However we don't want to increase
	// it too much because there are quite a few
	// BufferedIndexInputs created during merging. See
	// LUCENE-888 for details.
	/**
	* A buffer size for merges set to {@value #MERGE_BUFFER_SIZE}.
	*/
	public static final int MERGE_BUFFER_SIZE = 4096;

	private int bufferSize = BUFFER_SIZE;

	private ByteBuffer buffer = EMPTY_BYTEBUFFER;

	private long bufferStart = 0; // position in file of buffer

	@Override
	public final byte readByte() throws IOException {
	if (buffer.hasRemaining() == false) {
	refill();
	}
	return buffer.get();
	}

	public BufferedIndexInput(String resourceDesc) {
	this(resourceDesc, BUFFER_SIZE);
	}

	public BufferedIndexInput(String resourceDesc, IOContext context) {
	this(resourceDesc, bufferSize(context));
	}

	/** Inits BufferedIndexInput with a specific bufferSize */
	public BufferedIndexInput(String resourceDesc, int bufferSize) {
	super(resourceDesc);
	checkBufferSize(bufferSize);
	this.bufferSize = bufferSize;
	}

	/** Change the buffer size used by this IndexInput */
	public final void setBufferSize(int newSize) {
	assert buffer == EMPTY_BYTEBUFFER \|\| bufferSize == buffer.capacity(): "buffer=" + buffer + " bufferSize=" + bufferSize + " buffer.length=" + (buffer != null ? buffer.capacity() : 0);
	if (newSize != bufferSize) {
	checkBufferSize(newSize);
	bufferSize = newSize;
	if (buffer != EMPTY_BYTEBUFFER) {
	// Resize the existing buffer and carefully save as
	// many bytes as possible starting from the current
	// bufferPosition
	ByteBuffer newBuffer = ByteBuffer.allocate(newSize);
	assert newBuffer.order() == ByteOrder.BIG_ENDIAN;
	if (buffer.remaining() > newBuffer.capacity()) {
	buffer.limit(buffer.position() + newBuffer.capacity());
	}
	assert buffer.remaining() <= newBuffer.capacity();
	newBuffer.put(buffer);
	newBuffer.flip();
	buffer = newBuffer;
	}
	}
	}

	/** Returns buffer size. @see #setBufferSize */
	public final int getBufferSize() {
	return bufferSize;
	}

	private void checkBufferSize(int bufferSize) {
	if (bufferSize < MIN_BUFFER_SIZE)
	throw new IllegalArgumentException("bufferSize must be at least MIN_BUFFER_SIZE (got " + bufferSize + ")");
	}

	@Override
	public final void readBytes(byte[] b, int offset, int len) throws IOException {
	readBytes(b, offset, len, true);
	}

	@Override
	public final void readBytes(byte[] b, int offset, int len, boolean useBuffer) throws IOException {
	int available = buffer.remaining();
	if(len <= available){
	// the buffer contains enough data to satisfy this request
	if(len>0) // to allow b to be null if len is 0...
	buffer.get(b, offset, len);
	} else {
	// the buffer does not have enough data. First serve all we've got.
	if(available > 0){
	buffer.get(b, offset, available);
	offset += available;
	len -= available;
	}
	// and now, read the remaining 'len' bytes:
	if (useBuffer && len<bufferSize){
	// If the amount left to read is small enough, and
	// we are allowed to use our buffer, do it in the usual
	// buffered way: fill the buffer and copy from it:
	refill();
	if(buffer.remaining()<len){
	// Throw an exception when refill() could not read len bytes:
	buffer.get(b, offset, buffer.remaining());
	throw new EOFException("read past EOF: " + this);
	} else {
	buffer.get(b, offset, len);
	}
	} else {
	// The amount left to read is larger than the buffer
	// or we've been asked to not use our buffer -
	// there's no performance reason not to read it all
	// at once. Note that unlike the previous code of
	// this function, there is no need to do a seek
	// here, because there's no need to reread what we
	// had in the buffer.
	long after = bufferStart+buffer.position()+len;
	if(after > length())
	throw new EOFException("read past EOF: " + this);
	readInternal(ByteBuffer.wrap(b, offset, len));
	bufferStart = after;
	buffer.limit(0); // trigger refill() on read
	}
	}
	}

	@Override
	public final short readShort() throws IOException {
	if (Short.BYTES <= buffer.remaining()) {
	return buffer.getShort();
	} else {
	return super.readShort();
	}
	}

	@Override
	public final int readInt() throws IOException {
	if (Integer.BYTES <= buffer.remaining()) {
	return buffer.getInt();
	} else {
	return super.readInt();
	}
	}

	@Override
	public final long readLong() throws IOException {
	if (Long.BYTES <= buffer.remaining()) {
	return buffer.getLong();
	} else {
	return super.readLong();
	}
	}

	@Override
	public final int readVInt() throws IOException {
	if (5 <= buffer.remaining()) {
	byte b = buffer.get();
	if (b >= 0) return b;
	int i = b & 0x7F;
	b = buffer.get();
	i \|= (b & 0x7F) << 7;
	if (b >= 0) return i;
	b = buffer.get();
	i \|= (b & 0x7F) << 14;
	if (b >= 0) return i;
	b = buffer.get();
	i \|= (b & 0x7F) << 21;
	if (b >= 0) return i;
	b = buffer.get();
	// Warning: the next ands use 0x0F / 0xF0 - beware copy/paste errors:
	i \|= (b & 0x0F) << 28;
	if ((b & 0xF0) == 0) return i;
	throw new IOException("Invalid vInt detected (too many bits)");
	} else {
	return super.readVInt();
	}
	}

	@Override
	public final long readVLong() throws IOException {
	if (9 <= buffer.remaining()) {
	byte b = buffer.get();
	if (b >= 0) return b;
	long i = b & 0x7FL;
	b = buffer.get();
	i \|= (b & 0x7FL) << 7;
	if (b >= 0) return i;
	b = buffer.get();
	i \|= (b & 0x7FL) << 14;
	if (b >= 0) return i;
	b = buffer.get();
	i \|= (b & 0x7FL) << 21;
	if (b >= 0) return i;
	b = buffer.get();
	i \|= (b & 0x7FL) << 28;
	if (b >= 0) return i;
	b = buffer.get();
	i \|= (b & 0x7FL) << 35;
	if (b >= 0) return i;
	b = buffer.get();
	i \|= (b & 0x7FL) << 42;
	if (b >= 0) return i;
	b = buffer.get();
	i \|= (b & 0x7FL) << 49;
	if (b >= 0) return i;
	b = buffer.get();
	i \|= (b & 0x7FL) << 56;
	if (b >= 0) return i;
	throw new IOException("Invalid vLong detected (negative values disallowed)");
	} else {
	return super.readVLong();
	}
	}

	@Override
	public final byte readByte(long pos) throws IOException {
	long index = pos - bufferStart;
	if (index < 0 \|\| index >= buffer.limit()) {
	bufferStart = pos;
	buffer.limit(0); // trigger refill() on read
	seekInternal(pos);
	refill();
	index = 0;
	}
	return buffer.get((int) index);
	}

	@Override
	public final short readShort(long pos) throws IOException {
	long index = pos - bufferStart;
	if (index < 0 \|\| index >= buffer.limit()-1) {
	bufferStart = pos;
	buffer.limit(0); // trigger refill() on read
	seekInternal(pos);
	refill();
	index = 0;
	}
	return buffer.getShort((int) index);
	}

	@Override
	public final int readInt(long pos) throws IOException {
	long index = pos - bufferStart;
	if (index < 0 \|\| index >= buffer.limit()-3) {
	bufferStart = pos;
	buffer.limit(0); // trigger refill() on read
	seekInternal(pos);
	refill();
	index = 0;
	}
	return buffer.getInt((int) index);
	}

	@Override
	public final long readLong(long pos) throws IOException {
	long index = pos - bufferStart;
	if (index < 0 \|\| index >= buffer.limit()-7) {
	bufferStart = pos;
	buffer.limit(0); // trigger refill() on read
	seekInternal(pos);
	refill();
	index = 0;
	}
	return buffer.getLong((int) index);
	}

	private void refill() throws IOException {
	long start = bufferStart + buffer.position();
	long end = start + bufferSize;
	if (end > length()) // don't read past EOF
	end = length();
	int newLength = (int)(end - start);
	if (newLength <= 0)
	throw new EOFException("read past EOF: " + this);

	if (buffer == EMPTY_BYTEBUFFER) {
	buffer = ByteBuffer.allocate(bufferSize); // allocate buffer lazily
	seekInternal(bufferStart);
	}
	buffer.position(0);
	buffer.limit(newLength);
	bufferStart = start;
	readInternal(buffer);
	// Make sure sub classes don't mess up with the buffer.
	assert buffer.order() == ByteOrder.BIG_ENDIAN : buffer.order();
	assert buffer.remaining() == 0 : "should have thrown EOFException";
	assert buffer.position() == newLength;
	buffer.flip();
	}

	/** Expert: implements buffer refill. Reads bytes from the current position
	* in the input.
	* @param b the buffer to read bytes into
	*/
	protected abstract void readInternal(ByteBuffer b) throws IOException;

	@Override
	public final long getFilePointer() { return bufferStart + buffer.position(); }

	@Override
	public final void seek(long pos) throws IOException {
	if (pos >= bufferStart && pos < (bufferStart + buffer.limit()))
	buffer.position((int)(pos - bufferStart)); // seek within buffer
	else {
	bufferStart = pos;
	buffer.limit(0); // trigger refill() on read
	seekInternal(pos);
	}
	}

	/** Expert: implements seek. Sets current position in this file, where the
	* next {@link #readInternal(ByteBuffer)} will occur.
	* @see #readInternal(ByteBuffer)
	*/
	protected abstract void seekInternal(long pos) throws IOException;

	@Override
	public BufferedIndexInput clone() {
	BufferedIndexInput clone = (BufferedIndexInput)super.clone();

	clone.buffer = EMPTY_BYTEBUFFER;
	clone.bufferStart = getFilePointer();

	return clone;
	}

	@Override
	public IndexInput slice(String sliceDescription, long offset, long length) throws IOException {
	return wrap(sliceDescription, this, offset, length);
	}

	/**
	* Returns default buffer sizes for the given {@link IOContext}
	*/
	public static int bufferSize(IOContext context) {
	switch (context.context) {
	case MERGE:
	return MERGE_BUFFER_SIZE;
	default:
	return BUFFER_SIZE;
	}
	}

	/**
	* Wraps a portion of another IndexInput with buffering.
	* <p><b>Please note:</b> This is in most cases ineffective, because it may double buffer!
	*/
	public static BufferedIndexInput wrap(String sliceDescription, IndexInput other, long offset, long length) {
	return new SlicedIndexInput(sliceDescription, other, offset, length);
	}

	/**
	* Implementation of an IndexInput that reads from a portion of a file.
	*/
	private static final class SlicedIndexInput extends BufferedIndexInput {
	IndexInput base;
	long fileOffset;
	long length;

	SlicedIndexInput(String sliceDescription, IndexInput base, long offset, long length) {
	super((sliceDescription == null) ? base.toString() : (base.toString() + " [slice=" + sliceDescription + "]"), BufferedIndexInput.BUFFER_SIZE);
	if (offset < 0 \|\| length < 0 \|\| offset + length > base.length()) {
	throw new IllegalArgumentException("slice() " + sliceDescription + " out of bounds: " + base);
	}
	this.base = base.clone();
	this.fileOffset = offset;
	this.length = length;
	}

	@Override
	public SlicedIndexInput clone() {
	SlicedIndexInput clone = (SlicedIndexInput)super.clone();
	clone.base = base.clone();
	clone.fileOffset = fileOffset;
	clone.length = length;
	return clone;
	}

	@Override
	protected void readInternal(ByteBuffer b) throws IOException {
	long start = getFilePointer();
	if (start + b.remaining() > length) {
	throw new EOFException("read past EOF: " + this);
	}
	base.seek(fileOffset + start);
	base.readBytes(b.array(), b.position(), b.remaining());
	b.position(b.position() + b.remaining());
	}

	@Override
	protected void seekInternal(long pos) {}

	@Override
	public void close() throws IOException {
	base.close();
	}

	@Override
	public long length() {
	return length;
	}
	}
	}