protected void _doAppendChunked(long[] buffer, int offset, int length)
{
// first: append length prefix
if (!_head.tryAppend(length)) {
final LongsSegment seg = _head;
seg.finishWriting();
// and allocate, init-for-writing new one:
LongsSegment newSeg = _reuseFree().initForWriting();
seg.relink(newSeg);
_head = newSeg;
if (!_head.tryAppend(length)) {