byteAt method
Implementation
@override
int byteAt(int byteOffset) {
RangeError.checkValidIndex(byteOffset, this, 'byteOffset', _byteLength);
final pieceIndex = _pieceIndex(byteOffset);
final pieceStart = pieceIndex == 0 ? 0 : _pieceEnds[pieceIndex - 1];
return _pieces[pieceIndex][byteOffset - pieceStart];
}