private long getOffset(final long pos) throws IOException {
        final long seekPos = pos + windowSegmentStart;
        if (seekPos == -1) {
            // Implies start of file
            return 0;
        }

        ((SeekableInputStream) indexInputStream).seek((seekPos) * INT8);

        StreamUtil.eagerRead(indexInputStream, eightBytes);
        longBuffer.rewind();
        return longBuffer.get();
    }
Gets the byte offset in the data file for a specified position in the
index.

@param pos The index position.
@return The byte offset in the data file.
stroom-data/stroom-data-store-impl-fs/src/main/java/stroom/data/store/impl/fs/RASegmentInputStream.java