Add SelectCoinsSRD function

Author: achow101

src/wallet/coinselection.cpp

@@ -5,9 +5,11 @@
 #include <wallet/coinselection.h>
 
 #include <policy/feerate.h>
+#include <util/check.h>
 #include <util/system.h>
 #include <util/moneystr.h>
 
+#include <numeric>
 #include <optional>
 
 // Descending order comparator
@@ -168,6 +170,30 @@ bool SelectCoinsBnB(std::vector<OutputGroup>& utxo_pool, const CAmount& selectio
     return true;
 }
 
+std::optional<std::pair<std::set<CInputCoin>, CAmount>> SelectCoinsSRD(const std::vector<OutputGroup>& utxo_pool, CAmount target_value)
+{
+    std::set<CInputCoin> out_set;
+    CAmount value_ret = 0;
+
+    std::vector<size_t> indexes;
+    indexes.resize(utxo_pool.size());
+    std::iota(indexes.begin(), indexes.end(), 0);
+    Shuffle(indexes.begin(), indexes.end(), FastRandomContext());
+
+    CAmount selected_eff_value = 0;
+    for (const size_t i : indexes) {
+        const OutputGroup& group = utxo_pool.at(i);
+        Assume(group.GetSelectionAmount() > 0);
+        selected_eff_value += group.GetSelectionAmount();
+        value_ret += group.m_value;
+        util::insert(out_set, group.m_outputs);
+        if (selected_eff_value >= target_value) {
+            return std::make_pair(out_set, value_ret);
+        }
+    }
+    return std::nullopt;
+}
+
 static void ApproximateBestSubset(const std::vector<OutputGroup>& groups, const CAmount& nTotalLower, const CAmount& nTargetValue,
                                   std::vector<char>& vfBest, CAmount& nBest, int iterations = 1000)
 {

src/wallet/coinselection.h

@@ -10,6 +10,8 @@
 #include <primitives/transaction.h>
 #include <random.h>
 
+#include <optional>
+
 //! target minimum change amount
 static constexpr CAmount MIN_CHANGE{COIN / 100};
 //! final minimum change amount after paying for fees
@@ -183,6 +185,15 @@ struct OutputGroup
 
 bool SelectCoinsBnB(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, const CAmount& cost_of_change, std::set<CInputCoin>& out_set, CAmount& value_ret);
 
+/** Select coins by Single Random Draw. OutputGroups are selected randomly from the eligible
+ * outputs until the target is satisfied
+ *
+ * @param[in]  utxo_pool    The positive effective value OutputGroups eligible for selection
+ * @param[in]  target_value The target value to select for
+ * @returns If successful, a pair of set of outputs and total selected value, otherwise, std::nullopt
+ */
+std::optional<std::pair<std::set<CInputCoin>, CAmount>> SelectCoinsSRD(const std::vector<OutputGroup>& utxo_pool, CAmount target_value);
+
 // Original coin selection algorithm as a fallback
 bool KnapsackSolver(const CAmount& nTargetValue, std::vector<OutputGroup>& groups, std::set<CInputCoin>& setCoinsRet, CAmount& nValueRet);