From a54c7b94f8825e9b52fec9066fe7c1d5b6f53482 Mon Sep 17 00:00:00 2001 From: Alex Morcos Date: Fri, 25 Aug 2017 14:46:07 -0500 Subject: [PATCH] Fix rounding errors in calculation of minimum change size --- src/wallet/wallet.cpp | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp index 291bcc7a20..503354b663 100644 --- a/src/wallet/wallet.cpp +++ b/src/wallet/wallet.cpp @@ -2861,13 +2861,15 @@ bool CWallet::CreateTransaction(const std::vector& vecSend, CWalletT // new inputs. We now know we only need the smaller fee // (because of reduced tx size) and so we should add a // change output. Only try this once. - CAmount fee_needed_for_change = GetMinimumFee(change_prototype_size, coin_control, ::mempool, ::feeEstimator, nullptr); - CAmount minimum_value_for_change = GetDustThreshold(change_prototype_txout, discard_rate); - CAmount max_excess_fee = fee_needed_for_change + minimum_value_for_change; - if (nFeeRet > nFeeNeeded + max_excess_fee && nChangePosInOut == -1 && nSubtractFeeFromAmount == 0 && pick_new_inputs) { - pick_new_inputs = false; - nFeeRet = nFeeNeeded + fee_needed_for_change; - continue; + if (nChangePosInOut == -1 && nSubtractFeeFromAmount == 0 && pick_new_inputs) { + unsigned int tx_size_with_change = nBytes + change_prototype_size + 2; // Add 2 as a buffer in case increasing # of outputs changes compact size + CAmount fee_needed_with_change = GetMinimumFee(tx_size_with_change, coin_control, ::mempool, ::feeEstimator, nullptr); + CAmount minimum_value_for_change = GetDustThreshold(change_prototype_txout, discard_rate); + if (nFeeRet >= fee_needed_with_change + minimum_value_for_change) { + pick_new_inputs = false; + nFeeRet = fee_needed_with_change; + continue; + } } // If we have change output already, just increase it