Index: src/java/org/apache/lucene/store/BufferedIndexInput.java
===================================================================
--- src/java/org/apache/lucene/store/BufferedIndexInput.java	(revision 466973)
+++ src/java/org/apache/lucene/store/BufferedIndexInput.java	(working copy)
@@ -34,19 +34,37 @@
     return buffer[bufferPosition++];
   }
 
-  public void readBytes(byte[] b, int offset, int len)
-       throws IOException {
-    if (len < BUFFER_SIZE) {
-      for (int i = 0; i < len; i++)		  // read byte-by-byte
-	b[i + offset] = (byte)readByte();
-    } else {					  // read all-at-once
-      long start = getFilePointer();
-      seekInternal(start);
-      readInternal(b, offset, len);
-
-      bufferStart = start + len;		  // adjust stream variables
-      bufferPosition = 0;
-      bufferLength = 0;				  // trigger refill() on read
+  public void readBytes(byte[] b, int offset, int len) throws IOException {
+    if(len <= (bufferLength-bufferPosition)){
+      // the buffer contains enough data to satistfy this request
+      System.arraycopy(buffer, bufferPosition, b, offset, len);
+      bufferPosition+=len;
+    } else {
+      // the buffer does not have enough data. First serve all we've got.
+      int available = bufferLength - bufferPosition;
+      if(available > 0){
+        System.arraycopy(buffer, bufferPosition, b, offset, available);
+        offset += available;
+        len -= available;
+        bufferPosition += available;
+      }
+      // and now, read the remaining 'len' bytes:
+      if(len<BUFFER_SIZE){
+        // If the amount left to read is small enough, do it in the usual
+        // buffered way: fill the buffer and copy from it:
+        refill();
+        System.arraycopy(buffer, 0, b, offset, len);
+        bufferPosition=len;
+      } else {
+        // The amount left to read is larger than the 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.
+        readInternal(b, offset, len);
+        bufferStart += bufferPosition+len;   // adjust stream variables
+        bufferPosition = 0;
+        bufferLength = 0;                    // trigger refill() on read
+      }
     }
   }
 
Index: src/test/org/apache/lucene/store/TestBufferedIndexInput.java
===================================================================
--- src/test/org/apache/lucene/store/TestBufferedIndexInput.java	(revision 0)
+++ src/test/org/apache/lucene/store/TestBufferedIndexInput.java	(revision 0)
@@ -0,0 +1,83 @@
+package org.apache.lucene.store;
+
+import java.io.IOException;
+
+import junit.framework.TestCase;
+
+public class TestBufferedIndexInput extends TestCase {
+	// Call readByte() repeatedly, past the buffer boundary, and see that it
+	// is working as expected.
+	// Our input comes from a dynamically generated/ "file" - see
+	// MyBufferedIndexInput below.
+    public void testReadByte() throws Exception {
+    	MyBufferedIndexInput input = new MyBufferedIndexInput(); 
+    	for(int i=0; i<BufferedIndexInput.BUFFER_SIZE*10; i++){
+     		assertEquals(input.readByte(), byten(i));
+    	}
+    }
+ 
+	// Call readBytes() repeatedly, with various chunk sizes (from 1 byte to
+    // larger than the buffer size), and see that it returns the bytes we expect.
+	// Our input comes from a dynamically generated "file" -
+    // see MyBufferedIndexInput below.
+    public void testReadBytes() throws Exception {
+    	MyBufferedIndexInput input = new MyBufferedIndexInput();
+    	int pos=0;
+    	// gradually increasing size:
+    	for(int size=1; size<BufferedIndexInput.BUFFER_SIZE*10; size=size+size/200+1){
+    		checkReadBytes(input, size, pos);
+    		pos+=size;
+    	}
+    	// wildly fluctuating size:
+    	for(long i=0; i<1000; i++){
+    		// The following function generates a fluctuating (but repeatable)
+    		// size, sometimes small (<100) but sometimes large (>10000)
+    		int size1 = (int)( i%7 + 7*(i%5)+ 7*5*(i%3) + 5*5*3*(i%2));
+    		int size2 = (int)( i%11 + 11*(i%7)+ 11*7*(i%5) + 11*7*5*(i%3) + 11*7*5*3*(i%2) );
+    		int size = (i%3==0)?size2*10:size1; 
+    		checkReadBytes(input, size, pos);
+    		pos+=size;
+    	}
+    	// constant small size (7 bytes):
+    	for(int i=0; i<BufferedIndexInput.BUFFER_SIZE; i++){
+    		checkReadBytes(input, 7, pos);
+    		pos+=7;
+    	}
+    }
+   public void checkReadBytes(BufferedIndexInput input, int size, int pos) throws IOException{
+	   // Just to see that "offset" is treated properly in readBytes(), we
+	   // add an arbitrary offset at the beginning of the array
+	   int offset = size % 10; // arbitrary
+	   byte[] b = new byte[offset+size];
+	   input.readBytes(b, offset, size);
+	   for(int i=0; i<size; i++){
+		   assertEquals(b[offset+i], byten(pos+i));
+	   }
+   }
+
+    // byten emulates a file - byten(n) returns the n'th byte in that file.
+    // MyBufferedIndexInput reads this "file".
+    private static byte byten(long n){
+    	return (byte)(n*n%256);
+    }
+    private static class MyBufferedIndexInput extends BufferedIndexInput {
+    	long pos=0;
+		protected void readInternal(byte[] b, int offset, int length) throws IOException {
+			for(int i=offset; i<offset+length; i++)
+				b[i] = byten(pos++);
+		}
+
+		protected void seekInternal(long pos) throws IOException {
+			this.pos = pos;
+		}
+
+		public void close() throws IOException {
+		}
+
+		public long length() {
+			// an infinite file. Unfortunatelty, this length() is actually used
+			// in refill(), so we need to give it a real value
+			return Long.MAX_VALUE;
+		}
+    }
+}