def METHOD_NAME(self, current_tip=None):
    if current_tip is None:
        current_tip = self.currentBlock
    r = []
    counter = 0
    step = 1
    lastBlock = self.get(current_tip)
    while lastBlock is not None:
        r.append(lastBlock.hashPrevBlock)
        for i in range(step):
            lastBlock = self.get(lastBlock.hashPrevBlock)
            if lastBlock is None:
                break
        counter += 1
        if counter > 10:
            step *= 2
    locator = CBlockLocator()
    locator.vHave = r
    return locator