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Try to reduce change output to make needed fee in CreateTransaction

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Once we've picked coins and dummy-signed the transaction to calculate fee, if we don't have sufficient fee, then try to meet the fee by reducing change before resorting to picking new coins.
This commit is contained in:
Alex Morcos 2017-01-05 09:10:08 -05:00
parent f646275b90
commit 42f5ce4093
2 changed files with 15 additions and 1 deletions
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12
src/wallet/wallet.cpp
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@ -2537,6 +2537,18 @@ bool CWallet::CreateTransaction(const vector<CRecipient>& vecSend, CWalletTx& wt
if (nFeeRet >= nFeeNeeded)
break; // Done, enough fee included.
// Try to reduce change to include necessary fee
if (nChangePosInOut != -1 && nSubtractFeeFromAmount == 0) {
CAmount additionalFeeNeeded = nFeeNeeded - nFeeRet;
vector<CTxOut>::iterator change_position = txNew.vout.begin()+nChangePosInOut;
// Only reduce change if remaining amount is still a large enough output.
if (change_position->nValue >= MIN_FINAL_CHANGE + additionalFeeNeeded) {
change_position->nValue -= additionalFeeNeeded;
nFeeRet += additionalFeeNeeded;
break; // Done, able to increase fee from change
}
}
// Include more fee and try again.
nFeeRet = nFeeNeeded;
continue;

4
src/wallet/wallet.h
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@ -48,8 +48,10 @@ static const CAmount DEFAULT_TRANSACTION_FEE = 0;
static const CAmount DEFAULT_FALLBACK_FEE = 20000;
//! -mintxfee default
static const CAmount DEFAULT_TRANSACTION_MINFEE = 1000;
//! minimum change amount
//! target minimum change amount
static const CAmount MIN_CHANGE = CENT;
//! final minimum change amount after paying for fees
static const CAmount MIN_FINAL_CHANGE = MIN_CHANGE/2;
//! Default for -spendzeroconfchange
static const bool DEFAULT_SPEND_ZEROCONF_CHANGE = true;
//! Default for -sendfreetransactions