Value GetNetworkHashPS(int lookup, int height) {
     CBlockIndex *pb = pindexBest;
 
     if (height >= 0 && height < nBestHeight)
         pb = FindBlockByHeight(height);
 
     if (pb == NULL || !pb->nHeight)
         return 0;
 
     // If lookup is -1, then use blocks since last difficulty change.
     if (lookup <= 0)
         lookup = pb->nHeight % 2016 + 1;
 
     // If lookup is larger than chain, then set it to chain length.
     if (lookup > pb->nHeight)
         lookup = pb->nHeight;
 
     CBlockIndex *pb0 = pb;
     int64 minTime = pb0->GetBlockTime();
     int64 maxTime = minTime;
     for (int i = 0; i < lookup; i++) {
         pb0 = pb0->pprev;
         int64 time = pb0->GetBlockTime();
         minTime = std::min(time, minTime);
         maxTime = std::max(time, maxTime);
     }
 
     // In case there's a situation where minTime == maxTime, we don't want a divide by zero exception.
     if (minTime == maxTime)
         return 0;
 
     uint256 workDiff = pb->nChainWork - pb0->nChainWork;
     int64 timeDiff = maxTime - minTime;
 
     return (boost::int64_t)(workDiff.getdouble() / timeDiff);
 }
 
 Value getnetworkhashps(const Array& params, bool fHelp)
 {
     if (fHelp || params.size() > 2)
         throw runtime_error(
             "getnetworkhashps [blocks] [height]\n"
             "Returns the estimated network hashes per second based on the last 120 blocks.\n"
             "Pass in [blocks] to override # of blocks, -1 specifies since last difficulty change.\n"
             "Pass in [height] to estimate the network speed at the time when a certain block was found.");
 
     return GetNetworkHashPS(params.size() > 0 ? params[0].get_int() : 120, params.size() > 1 ? params[1].get_int() : -1);
 }