private static IDictionary <string, FileEntry> ReadLegacyEntries(IndexInput stream, int firstInt)
        {
            IDictionary <string, FileEntry> entries = new Dictionary <string, FileEntry>();
            int  count;
            bool stripSegmentName;

            if (firstInt < CompoundFileWriter.FORMAT_PRE_VERSION)
            {
                if (firstInt < CompoundFileWriter.FORMAT_NO_SEGMENT_PREFIX)
                {
                    throw new CorruptIndexException("Incompatible format version: "
                                                    + firstInt + " expected >= " + CompoundFileWriter.FORMAT_NO_SEGMENT_PREFIX + " (resource: " + stream + ")");
                }
                // It's a post-3.1 index, read the count.
                count            = stream.ReadVInt32();
                stripSegmentName = false;
            }
            else
            {
                count            = firstInt;
                stripSegmentName = true;
            }

            // read the directory and init files
            long      streamLength = stream.Length;
            FileEntry entry        = null;

            for (int i = 0; i < count; i++)
            {
                long offset = stream.ReadInt64();
                if (offset < 0 || offset > streamLength)
                {
                    throw new CorruptIndexException("Invalid CFS entry offset: " + offset + " (resource: " + stream + ")");
                }
                string id = stream.ReadString();

                if (stripSegmentName)
                {
                    // Fix the id to not include the segment names. this is relevant for
                    // pre-3.1 indexes.
                    id = IndexFileNames.StripSegmentName(id);
                }

                if (entry != null)
                {
                    // set length of the previous entry
                    entry.Length = offset - entry.Offset;
                }

                entry        = new FileEntry();
                entry.Offset = offset;

                FileEntry previous = entries.Put(id, entry);
                if (previous != null)
                {
                    throw new CorruptIndexException("Duplicate cfs entry id=" + id + " in CFS: " + stream);
                }
            }

            // set the length of the final entry
            if (entry != null)
            {
                entry.Length = streamLength - entry.Offset;
            }

            return(entries);
        }
        /// <summary>
        /// Helper method that reads CFS entries from an input stream </summary>
        private static IDictionary <string, FileEntry> ReadEntries(IndexInputSlicer handle, Directory dir, string name)
        {
            IOException        priorE        = null;
            IndexInput         stream        = null;
            ChecksumIndexInput entriesStream = null;

            // read the first VInt. If it is negative, it's the version number
            // otherwise it's the count (pre-3.1 indexes)
            try
            {
                IDictionary <string, FileEntry> mapping;
#pragma warning disable 612, 618
                stream = handle.OpenFullSlice();
#pragma warning restore 612, 618
                int firstInt = stream.ReadVInt32();
                // impossible for 3.0 to have 63 files in a .cfs, CFS writer was not visible
                // and separate norms/etc are outside of cfs.
                if (firstInt == CODEC_MAGIC_BYTE1)
                {
                    sbyte secondByte = (sbyte)stream.ReadByte();
                    sbyte thirdByte  = (sbyte)stream.ReadByte();
                    sbyte fourthByte = (sbyte)stream.ReadByte();
                    if (secondByte != CODEC_MAGIC_BYTE2 || thirdByte != CODEC_MAGIC_BYTE3 || fourthByte != CODEC_MAGIC_BYTE4)
                    {
                        throw new CorruptIndexException("Illegal/impossible header for CFS file: " + secondByte + "," + thirdByte + "," + fourthByte);
                    }
                    int    version         = CodecUtil.CheckHeaderNoMagic(stream, CompoundFileWriter.DATA_CODEC, CompoundFileWriter.VERSION_START, CompoundFileWriter.VERSION_CURRENT);
                    string entriesFileName = IndexFileNames.SegmentFileName(
                        IndexFileNames.StripExtension(name), "",
                        IndexFileNames.COMPOUND_FILE_ENTRIES_EXTENSION);
                    entriesStream = dir.OpenChecksumInput(entriesFileName, IOContext.READ_ONCE);
                    CodecUtil.CheckHeader(entriesStream, CompoundFileWriter.ENTRY_CODEC, CompoundFileWriter.VERSION_START, CompoundFileWriter.VERSION_CURRENT);
                    int numEntries = entriesStream.ReadVInt32();
                    mapping = new Dictionary <string, FileEntry>(numEntries);
                    for (int i = 0; i < numEntries; i++)
                    {
                        FileEntry fileEntry = new FileEntry();
                        string    id        = entriesStream.ReadString();
                        FileEntry previous  = mapping.Put(id, fileEntry);
                        if (previous != null)
                        {
                            throw new CorruptIndexException("Duplicate cfs entry id=" + id + " in CFS: " + entriesStream);
                        }
                        fileEntry.Offset = entriesStream.ReadInt64();
                        fileEntry.Length = entriesStream.ReadInt64();
                    }
                    if (version >= CompoundFileWriter.VERSION_CHECKSUM)
                    {
                        CodecUtil.CheckFooter(entriesStream);
                    }
                    else
                    {
#pragma warning disable 612, 618
                        CodecUtil.CheckEOF(entriesStream);
#pragma warning restore 612, 618
                    }
                }
                else
                {
                    // TODO remove once 3.x is not supported anymore
                    mapping = ReadLegacyEntries(stream, firstInt);
                }
                return(mapping);
            }
            catch (IOException ioe)
            {
                priorE = ioe;
            }
            finally
            {
                IOUtils.DisposeWhileHandlingException(priorE, stream, entriesStream);
            }
            // this is needed until Java 7's real try-with-resources:
            throw new InvalidOperationException("impossible to get here");
        }