Index: lucene/src/test/org/apache/lucene/index/TestTermVectorsReader.java
===================================================================
--- lucene/src/test/org/apache/lucene/index/TestTermVectorsReader.java	(revision 1135329)
+++ lucene/src/test/org/apache/lucene/index/TestTermVectorsReader.java	(working copy)
@@ -390,8 +390,6 @@
       fail();
     } catch (IOException e) {
       // expected exception
-    } catch (IllegalArgumentException e) {
-      // mmapdir will give us this from java.nio.Buffer.position()
     } finally {
       reader.close();
     }
@@ -402,8 +400,6 @@
       fail();
     } catch (IOException e) {
       // expected exception
-    } catch (IllegalArgumentException e) {
-      // mmapdir will give us this from java.nio.Buffer.position()
     } finally {
       reader.close();
     }
Index: lucene/src/test/org/apache/lucene/store/TestMultiMMap.java
===================================================================
--- lucene/src/test/org/apache/lucene/store/TestMultiMMap.java	(revision 1135329)
+++ lucene/src/test/org/apache/lucene/store/TestMultiMMap.java	(working copy)
@@ -25,6 +25,7 @@
 import org.apache.lucene.document.Field;
 import org.apache.lucene.index.IndexReader;
 import org.apache.lucene.index.RandomIndexWriter;
+import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.LuceneTestCase;
 import org.apache.lucene.util._TestUtil;
 
@@ -40,11 +41,70 @@
   
   @Override
   public void setUp() throws Exception {
-      super.setUp();
-      workDir = _TestUtil.getTempDir("TestMultiMMap");
-      workDir.mkdirs();
+    super.setUp();
+    assumeTrue("test requires a jre that supports unmapping", MMapDirectory.UNMAP_SUPPORTED);
+    workDir = _TestUtil.getTempDir("TestMultiMMap");
+    workDir.mkdirs();
   }
+
+  public void testSeekZero() throws Exception {
+    for (int i = 0; i < 31; i++) {
+      MMapDirectory mmapDir = new MMapDirectory(_TestUtil.getTempDir("testSeekZero"));
+      mmapDir.setMaxChunkSize(1<<i);
+      IndexOutput io = mmapDir.createOutput("zeroBytes");
+      io.close();
+      IndexInput ii = mmapDir.openInput("zeroBytes");
+      ii.seek(0L);
+      ii.close();
+      mmapDir.close();
+    }
+  }
   
+  public void testSeekEnd() throws Exception {
+    for (int i = 0; i < 17; i++) {
+      MMapDirectory mmapDir = new MMapDirectory(_TestUtil.getTempDir("testSeekEnd"));
+      mmapDir.setMaxChunkSize(1<<i);
+      IndexOutput io = mmapDir.createOutput("bytes");
+      byte bytes[] = new byte[1<<i];
+      random.nextBytes(bytes);
+      io.writeBytes(bytes, bytes.length);
+      io.close();
+      IndexInput ii = mmapDir.openInput("bytes");
+      byte actual[] = new byte[1<<i];
+      ii.readBytes(actual, 0, actual.length);
+      assertEquals(new BytesRef(bytes), new BytesRef(actual));
+      ii.seek(1<<i);
+      ii.close();
+      mmapDir.close();
+    }
+  }
+  
+  public void testSeeking() throws Exception {
+    for (int i = 0; i < 10; i++) {
+      MMapDirectory mmapDir = new MMapDirectory(_TestUtil.getTempDir("testSeeking"));
+      mmapDir.setMaxChunkSize(1<<i);
+      IndexOutput io = mmapDir.createOutput("bytes");
+      byte bytes[] = new byte[1<<(i+1)]; // make sure we switch buffers
+      random.nextBytes(bytes);
+      io.writeBytes(bytes, bytes.length);
+      io.close();
+      IndexInput ii = mmapDir.openInput("bytes");
+      byte actual[] = new byte[1<<(i+1)]; // first read all bytes
+      ii.readBytes(actual, 0, actual.length);
+      assertEquals(new BytesRef(bytes), new BytesRef(actual));
+      for (int sliceStart = 0; sliceStart < bytes.length; sliceStart++) {
+        for (int sliceLength = 0; sliceLength < bytes.length - sliceStart; sliceLength++) {
+          byte slice[] = new byte[sliceLength];
+          ii.seek(sliceStart);
+          ii.readBytes(slice, 0, slice.length);
+          assertEquals(new BytesRef(bytes, sliceStart, sliceLength), new BytesRef(slice));
+        }
+      }
+      ii.close();
+      mmapDir.close();
+    }
+  }
+  
   public void testRandomChunkSizes() throws Exception {
     int num = atLeast(10);
     for (int i = 0; i < num; i++)
@@ -55,11 +115,12 @@
     File path = _TestUtil.createTempFile("mmap" + chunkSize, "tmp", workDir);
     path.delete();
     path.mkdirs();
-    MMapDirectory dir = new MMapDirectory(path);
-    dir.setMaxChunkSize(chunkSize);
+    MMapDirectory mmapDir = new MMapDirectory(path);
+    mmapDir.setMaxChunkSize(chunkSize);
     // we will map a lot, try to turn on the unmap hack
     if (MMapDirectory.UNMAP_SUPPORTED)
-      dir.setUseUnmap(true);
+      mmapDir.setUseUnmap(true);
+    MockDirectoryWrapper dir = new MockDirectoryWrapper(random, mmapDir);
     RandomIndexWriter writer = new RandomIndexWriter(random, dir, newIndexWriterConfig(TEST_VERSION_CURRENT, new MockAnalyzer(random)).setMergePolicy(newLogMergePolicy()));
     Document doc = new Document();
     Field docid = newField("docid", "0", Field.Store.YES, Field.Index.NOT_ANALYZED);
Index: lucene/src/java/org/apache/lucene/store/MMapDirectory.java
===================================================================
--- lucene/src/java/org/apache/lucene/store/MMapDirectory.java	(revision 1135329)
+++ lucene/src/java/org/apache/lucene/store/MMapDirectory.java	(working copy)
@@ -79,8 +79,8 @@
  */
 public class MMapDirectory extends FSDirectory {
   private boolean useUnmapHack = UNMAP_SUPPORTED;
-  public static final int DEFAULT_MAX_BUFF = Constants.JRE_IS_64BIT ? Integer.MAX_VALUE : (256 * 1024 * 1024);
-  private int maxBBuf = DEFAULT_MAX_BUFF;
+  public static final int DEFAULT_MAX_BUFF = Constants.JRE_IS_64BIT ? (1 << 30) : (1 << 28);
+  private int power;
 
   /** Create a new MMapDirectory for the named location.
    *
@@ -91,6 +91,7 @@
    */
   public MMapDirectory(File path, LockFactory lockFactory) throws IOException {
     super(path, lockFactory);
+    setMaxChunkSize(DEFAULT_MAX_BUFF);
   }
 
   /** Create a new MMapDirectory for the named location and {@link NativeFSLockFactory}.
@@ -100,6 +101,7 @@
    */
   public MMapDirectory(File path) throws IOException {
     super(path, null);
+    setMaxChunkSize(DEFAULT_MAX_BUFF);
   }
 
   /**
@@ -180,23 +182,27 @@
    * Especially on 32 bit platform, the address space can be very fragmented,
    * so large index files cannot be mapped.
    * Using a lower chunk size makes the directory implementation a little
-   * bit slower (as the correct chunk must be resolved on each seek)
+   * bit slower (as the correct chunk may be resolved on lots of seeks)
    * but the chance is higher that mmap does not fail. On 64 bit
-   * Java platforms, this parameter should always be {@link Integer#MAX_VALUE},
+   * Java platforms, this parameter should always be {@code 1 << 30},
    * as the address space is big enough.
+   * <b>Please note:</b> This method always rounds down the chunk size
+   * to a power of 2.
    */
-  public void setMaxChunkSize(final int maxBBuf) {
+  public final void setMaxChunkSize(final int maxBBuf) {
     if (maxBBuf<=0)
       throw new IllegalArgumentException("Maximum chunk size for mmap must be >0");
-    this.maxBBuf=maxBBuf;
+    //System.out.println("Requested buf size: "+maxBBuf);
+    this.power = 31 - Integer.numberOfLeadingZeros(maxBBuf);
+    //System.out.println("Got buf size: "+getMaxChunkSize());
   }
   
   /**
    * Returns the current mmap chunk size.
    * @see #setMaxChunkSize
    */
-  public int getMaxChunkSize() {
-    return maxBBuf;
+  public final int getMaxChunkSize() {
+    return 1 << power;
   }
 
   /** Creates an IndexInput for the file with the given name. */
@@ -206,149 +212,54 @@
     File f = new File(getDirectory(), name);
     RandomAccessFile raf = new RandomAccessFile(f, "r");
     try {
-      return (raf.length() <= maxBBuf)
-             ? (IndexInput) new MMapIndexInput(raf)
-             : (IndexInput) new MultiMMapIndexInput(raf, maxBBuf);
+      return new MMapIndexInput(raf, power);
     } finally {
       raf.close();
     }
   }
 
-  private class MMapIndexInput extends IndexInput {
-
-    private ByteBuffer buffer;
-    private final long length;
-    private boolean isClone = false;
-
-    private MMapIndexInput(RandomAccessFile raf) throws IOException {
-        this.length = raf.length();
-        this.buffer = raf.getChannel().map(MapMode.READ_ONLY, 0, length);
-    }
-
-    @Override
-    public byte readByte() throws IOException {
-      try {
-        return buffer.get();
-      } catch (BufferUnderflowException e) {
-        throw new IOException("read past EOF");
-      }
-    }
-
-    @Override
-    public void readBytes(byte[] b, int offset, int len) throws IOException {
-      try {
-        buffer.get(b, offset, len);
-      } catch (BufferUnderflowException e) {
-        throw new IOException("read past EOF");
-      }
-    }
-    
-    @Override
-    public short readShort() throws IOException {
-      try {
-        return buffer.getShort();
-      } catch (BufferUnderflowException e) {
-        throw new IOException("read past EOF");
-      }
-    }
-
-    @Override
-    public int readInt() throws IOException {
-      try {
-        return buffer.getInt();
-      } catch (BufferUnderflowException e) {
-        throw new IOException("read past EOF");
-      }
-    }
-
-    @Override
-    public long readLong() throws IOException {
-      try {
-        return buffer.getLong();
-      } catch (BufferUnderflowException e) {
-        throw new IOException("read past EOF");
-      }
-    }
-    
-    @Override
-    public long getFilePointer() {
-      return buffer.position();
-    }
-
-    @Override
-    public void seek(long pos) throws IOException {
-      buffer.position((int)pos);
-    }
-
-    @Override
-    public long length() {
-      return length;
-    }
-
-    @Override
-    public Object clone() {
-      if (buffer == null)
-        throw new AlreadyClosedException("MMapIndexInput already closed");
-      MMapIndexInput clone = (MMapIndexInput)super.clone();
-      clone.isClone = true;
-      clone.buffer = buffer.duplicate();
-      return clone;
-    }
-
-    @Override
-    public void close() throws IOException {
-      // unmap the buffer (if enabled) and at least unset it for GC
-      try {
-        if (isClone || buffer == null) return;
-        cleanMapping(buffer);
-      } finally {
-        buffer = null;
-      }
-    }
-  }
-
   // Because Java's ByteBuffer uses an int to address the
   // values, it's necessary to access a file >
   // Integer.MAX_VALUE in size using multiple byte buffers.
-  private class MultiMMapIndexInput extends IndexInput {
+  private final class MMapIndexInput extends IndexInput {
   
     private ByteBuffer[] buffers;
   
-    private final long length;
+    private final long length, mask, maxBufSize;
+    private final int power;
   
     private int curBufIndex;
-    private final int maxBufSize;
   
     private ByteBuffer curBuf; // redundant for speed: buffers[curBufIndex]
   
     private boolean isClone = false;
     
-    public MultiMMapIndexInput(RandomAccessFile raf, int maxBufSize)
-      throws IOException {
+    MMapIndexInput(RandomAccessFile raf, int power) throws IOException {
       this.length = raf.length();
-      this.maxBufSize = maxBufSize;
+      this.power = power;
+      this.maxBufSize = 1L << power;
+      this.mask = maxBufSize - 1L;
       
-      if (maxBufSize <= 0)
-        throw new IllegalArgumentException("Non positive maxBufSize: "
-                                           + maxBufSize);
+      if (power < 0 || power > 30)
+        throw new IllegalArgumentException("Invalid power for buffer size: " + power);
       
-      if ((length / maxBufSize) > Integer.MAX_VALUE)
-        throw new IllegalArgumentException
-          ("RandomAccessFile too big for maximum buffer size: "
-           + raf.toString());
+      if ((length >>> power) >= Integer.MAX_VALUE)
+        throw new IllegalArgumentException("RandomAccessFile too big for maximum buffer size: " + raf.toString());
       
-      int nrBuffers = (int) (length / maxBufSize);
-      if (((long) nrBuffers * maxBufSize) <= length) nrBuffers++;
+      // we always allocate one more buffer, the last one may be a 0 byte one
+      final int nrBuffers = (int) (length >>> power) + 1;
       
+      //System.out.println("Length="+length+", Power=" + power + ", Mask=" + mask + ", nrBuffers=" + nrBuffers);
+      
       this.buffers = new ByteBuffer[nrBuffers];
       
-      long bufferStart = 0;
+      long bufferStart = 0L;
       FileChannel rafc = raf.getChannel();
       for (int bufNr = 0; bufNr < nrBuffers; bufNr++) { 
         int bufSize = (length > (bufferStart + maxBufSize))
-          ? maxBufSize
+          ? (int) maxBufSize
           : (int) (length - bufferStart);
-        this.buffers[bufNr] = rafc.map(MapMode.READ_ONLY,bufferStart,bufSize);
+        this.buffers[bufNr] = rafc.map(MapMode.READ_ONLY, bufferStart, bufSize);
         bufferStart += bufSize;
       }
       seek(0L);
@@ -364,6 +275,8 @@
           throw new IOException("read past EOF");
         curBuf = buffers[curBufIndex];
         curBuf.position(0);
+        if (!curBuf.hasRemaining())
+          throw new IOException("read past EOF");
         return curBuf.get();
       }
     }
@@ -418,15 +331,28 @@
     
     @Override
     public long getFilePointer() {
-      return ((long) curBufIndex * maxBufSize) + curBuf.position();
+      return (((long) curBufIndex) << power) + curBuf.position();
     }
   
     @Override
     public void seek(long pos) throws IOException {
-      curBufIndex = (int) (pos / maxBufSize);
-      curBuf = buffers[curBufIndex];
-      int bufOffset = (int) (pos - ((long) curBufIndex * maxBufSize));
-      curBuf.position(bufOffset);
+      // we use >> here to preserve negative, so we will catch AIOOBE:
+      final int bi = (int) (pos >> power);
+      try {
+        final ByteBuffer b = buffers[bi];
+        b.position((int) (pos & mask));
+        // write values, on exception all is unchanged
+        this.curBufIndex = bi;
+        this.curBuf = b;
+      } catch (ArrayIndexOutOfBoundsException aioobe) {
+        if (pos < 0L)
+          throw new IllegalArgumentException("Seeking to negative position");
+        throw new IOException("seek past EOF");
+      } catch (IllegalArgumentException iae) {
+        if (pos < 0L)
+          throw new IllegalArgumentException("Seeking to negative position");
+        throw new IOException("seek past EOF");
+      }
     }
   
     @Override
@@ -437,8 +363,8 @@
     @Override
     public Object clone() {
       if (buffers == null)
-        throw new AlreadyClosedException("MultiMMapIndexInput already closed");
-      MultiMMapIndexInput clone = (MultiMMapIndexInput)super.clone();
+        throw new AlreadyClosedException("MMapIndexInput already closed");
+      final MMapIndexInput clone = (MMapIndexInput)super.clone();
       clone.isClone = true;
       clone.buffers = new ByteBuffer[buffers.length];
       // Since most clones will use only one buffer, duplicate() could also be
@@ -449,9 +375,7 @@
       try {
         clone.seek(getFilePointer());
       } catch(IOException ioe) {
-        RuntimeException newException = new RuntimeException(ioe);
-        newException.initCause(ioe);
-        throw newException;
+        throw new RuntimeException("Should never happen", ioe);
       }
       return clone;
     }