Fixing wrong transaction size estimation

src/qt/sigmacoincontroldialog.cpp

@@ -509,54 +509,20 @@ void SigmaCoinControlDialog::updateLabels(WalletModel *model, QDialog* dialog)
         dPriorityInputs += (double)out.tx->vout[out.i].nValue * (out.nDepth+1);
 
         // Bytes
-        CTxDestination address;
-        int witnessversion = 0;
-        std::vector<unsigned char> witnessprogram;
-        if (out.tx->vout[out.i].scriptPubKey.IsWitnessProgram(witnessversion, witnessprogram))
-        {
-            nBytesInputs += (32 + 4 + 1 + (107 / WITNESS_SCALE_FACTOR) + 4);
-            fWitness = true;
-        }
-        else if(ExtractDestination(out.tx->vout[out.i].scriptPubKey, address))
-        {
-            CPubKey pubkey;
-            CKeyID *keyid = boost::get<CKeyID>(&address);
-            if (keyid && model->getPubKey(*keyid, pubkey))
-            {
-                nBytesInputs += (pubkey.IsCompressed() ? 148 : 180);
-                if (!pubkey.IsCompressed())
-                    nQuantityUncompressed++;
-            }
-            else
-                nBytesInputs += 148; // in all error cases, simply assume 148 here
-        }
-        else nBytesInputs += 148;
+        nBytesInputs += 74;
     }
 
     // calculation
     if (nQuantity > 0)
     {
-        // Bytes
-        nBytes = nBytesInputs + ((SigmaCoinControlDialog::payAmounts.size() > 0 ? SigmaCoinControlDialog::payAmounts.size() + 1 : 2) * 34) + 10; // always assume +1 output for change here
-        if (fWitness)
-        {
-            // there is some fudging in these numbers related to the actual virtual transaction size calculation that will keep this estimate from being exact.
-            // usually, the result will be an overestimate within a couple of satoshis so that the confirmation dialog ends up displaying a slightly smaller fee.
-            // also, the witness stack size value value is a variable sized integer. usually, the number of stack items will be well under the single byte var int limit.
-            nBytes += 2; // account for the serialized marker and flag bytes
-            nBytes += nQuantity; // account for the witness byte that holds the number of stack items for each input.
-        }
+        // Bytes         //1323 is script size for sigma spend
+        nBytes = nBytesInputs + vCoinControl.size() * 1323 +  10;
 
         // Priority
         double mempoolEstimatePriority = mempool.estimateSmartPriority(nTxConfirmTarget);
         dPriority = dPriorityInputs / (nBytes - nBytesInputs + (nQuantityUncompressed * 29)); // 29 = 180 - 151 (uncompressed public keys are over the limit. max 151 bytes of the input are ignored for priority)
         sPriorityLabel = SigmaCoinControlDialog::getPriorityLabel(dPriority, mempoolEstimatePriority);
 
-        // in the subtract fee from amount case, we can tell if zero change already and subtract the bytes, so that fee calculation afterwards is accurate
-        if (SigmaCoinControlDialog::fSubtractFeeFromAmount)
-            if (nAmount - nPayAmount == 0)
-                nBytes -= 34;
-
         // Fee
         nPayFee = CWallet::GetMinimumFee(nBytes, nTxConfirmTarget, mempool);
         if (nPayFee > 0 && coinControl->nMinimumTotalFee > nPayFee)
@@ -576,27 +542,25 @@ void SigmaCoinControlDialog::updateLabels(WalletModel *model, QDialog* dialog)
             nChange = nAmount - nPayAmount;
             if (!SigmaCoinControlDialog::fSubtractFeeFromAmount)
                 nChange -= nPayFee;
+        }
 
-            // Never create dust outputs; if we would, just add the dust to the fee.
-            if (nChange > 0 && nChange < MIN_CHANGE)
-            {
-                CTxOut txout(nChange, (CScript)std::vector<unsigned char>(24, 0));
-                if (txout.IsDust(::minRelayTxFee))
-                {
-                    if (SigmaCoinControlDialog::fSubtractFeeFromAmount) // dust-change will be raised until no dust
-                        nChange = txout.GetDustThreshold(::minRelayTxFee);
-                    else
-                    {
-                        nPayFee += nChange;
-                        nChange = 0;
-                    }
-                }
-            }
+        //update bytes
+        CAmount remChange = nChange;
 
-            if (nChange == 0 && !SigmaCoinControlDialog::fSubtractFeeFromAmount)
-                nBytes -= 34;
+        std::vector<int64_t> allDenoms;
+        sigma::GetAllDenoms(allDenoms);
+        for(int64_t denom : allDenoms) {
+            while (remChange >= denom) {
+                nBytes += 44;
+                remChange -= denom;
+            }
+            if(!remChange)
+                break;
         }
 
+        //add remaining to fee
+        nPayFee += remChange;
+
         // after fee
         nAfterFee = nAmount - nPayFee;
         if (nAfterFee < 0)

src/sigma/coin.cpp

@@ -157,6 +157,16 @@ void GetAllDenoms(std::vector<sigma::CoinDenomination>& denominations_out) {
     denominations_out.push_back(CoinDenomination::SIGMA_DENOM_0_05);
 }
 
+void GetAllDenoms(std::vector<int64_t>& denominations_out) {
+    denominations_out.push_back(100 * COIN);
+    denominations_out.push_back(25 * COIN);
+    denominations_out.push_back(10 * COIN);
+    denominations_out.push_back(1 * COIN);
+    denominations_out.push_back(50 * CENT);
+    denominations_out.push_back(10 * CENT);
+    denominations_out.push_back(5 * CENT);
+}
+
 //class PublicCoin
 PublicCoin::PublicCoin()
     : denomination(CoinDenomination::SIGMA_DENOM_1)

src/sigma/coin.h

@@ -35,6 +35,7 @@ bool RealNumberToDenomination(const double& value, CoinDenomination& denom_out);
 
 /// \brief Returns a list of all possible denominations in descending order of value.
 void GetAllDenoms(std::vector<sigma::CoinDenomination>& denominations_out);
+void GetAllDenoms(std::vector<int64_t>& denominations_out);
 
 class PublicCoin {
 public: