#define LN2SQUARED 0.4804530139182014246671025263266649717305529515945455
const uint8_t IBLT_CELL_MINIMUM = 2;
const uint16_t APPROX_ITEMS_THRESH = 600;
const uint16_t APPROX_ITEMS_THRESH_REDUCE_CHECK = 500;
const uint8_t APPROX_EXCESS_RATE = 4;
const float IBLT_DEFAULT_OVERHEAD = 1.5;
const uint8_t FILTER_CELL_SIZE = 1;
const uint8_t IBLT_FIXED_CELL_SIZE = 13;

// Infer various receiver quantities
uint64_t nReceiverExcessItems =
     std::max((int)(nReceiverUniverseItems - nItems), (int)(nSenderUniverseItems - nItems));
nReceiverExcessItems = std::max(0, (int)nReceiverExcessItems); // must be non-negative
nReceiverExcessItems =
        std::min((int)nReceiverUniverseItems, (int)nReceiverExcessItems); // must not exceed total mempool size
uint64_t nReceiverMissingItems = std::max(1, (int)(nItems - (nReceiverUniverseItems - nReceiverExcessItems)));

// Optimal symmetric differences between receiver and sender IBLTs
// This is the parameter "a" from the graphene paper
double optSymDiff = nReceiverMissingItems;
if (nItems <= nReceiverUniverseItems + nReceiverMissingItems)
    optSymDiff = OptimalSymDiff(nItems, nReceiverUniverseItems, nReceiverExcessItems, nReceiverMissingItems);

// Set false positive rate for Bloom filter based on optSymDiff
double fpr = BloomFalsePositiveRate(optSymDiff, nReceiverExcessItems);

// So far we have only made room for false positives in the IBLT
// Make more room for missing items
optSymDiff += nReceiverMissingItems;
uint64_t nIbltCells = std::max((int)IBLT_CELL_MINIMUM, (int)ceil(optSymDiff));

double CGrapheneSet::OptimalSymDiff(uint64_t nBlockTxs,
    uint64_t nReceiverPoolTx,
    uint64_t nReceiverExcessTxs,
    uint64_t nReceiverMissingTxs)
{
    uint16_t approx_items_thresh = version >= 4 ? APPROX_ITEMS_THRESH_REDUCE_CHECK : APPROX_ITEMS_THRESH;

    double optSymDiff;
    if (nBlockTxs >= approx_items_thresh && nReceiverExcessTxs >= nBlockTxs / APPROX_EXCESS_RATE)
       optSymDiff = ApproxOptimalSymDiff(nBlockTxs);
    else
        optSymDiff = BruteForceSymDiff(nBlockTxs, nReceiverPoolTx, nReceiverExcessTxs, nReceiverMissingTxs, MAX_CHECKSUM_BITS);
    return optSymDiff
}

double CGrapheneSet::ApproxOptimalSymDiff(uint64_t nBlockTxs)
{
    uint32_t nChecksumBits = 32;

    if (version >= 4)
        assert(nBlockTxs >= APPROX_ITEMS_THRESH_REDUCE_CHECK);
    else
        assert(nBlockTxs >= APPROX_ITEMS_THRESH);

    return std::max(1.0, std::round(FILTER_CELL_SIZE * nBlockTxs /
                                    ((nChecksumBits + 8 * IBLT_FIXED_CELL_SIZE) * IBLT_DEFAULT_OVERHEAD * LN2SQUARED)));
}