bool CBlock::CheckBlock() const
    {
        // These are checks that are independent of context
        // that can be verified before saving an orphan block.

        // Size limits
        if (vtx.empty() || vtx.size() > MAX_SIZE || ::GetSerializeSize(*this, SER_DISK) > MAX_SIZE)
            return error("CheckBlock() : size limits failed");
        ...
     }

static const unsigned int MAX_BLOCK_SIZE = 1000000;

if (nBlockSize + nTxSize >= MAX_BLOCK_SIZE - 10000)
     continue;