Avoid explicitly computing diagram; compare based on chunks

Author: sipa

src/policy/rbf.cpp

@@ -191,13 +191,13 @@ std::optional<std::pair<DiagramCheckError, std::string>> ImprovesFeerateDiagram(
                                                 int64_t replacement_vsize)
 {
     // Require that the replacement strictly improves the mempool's feerate diagram.
-    const auto diagram_results{pool.CalculateFeerateDiagramsForRBF(replacement_fees, replacement_vsize, direct_conflicts, all_conflicts)};
+    const auto chunk_results{pool.CalculateChunksForRBF(replacement_fees, replacement_vsize, direct_conflicts, all_conflicts)};
 
-    if (!diagram_results.has_value()) {
-        return std::make_pair(DiagramCheckError::UNCALCULABLE, util::ErrorString(diagram_results).original);
+    if (!chunk_results.has_value()) {
+        return std::make_pair(DiagramCheckError::UNCALCULABLE, util::ErrorString(chunk_results).original);
     }
 
-    if (!std::is_gt(CompareFeerateDiagram(diagram_results.value().second, diagram_results.value().first))) {
+    if (!std::is_gt(CompareChunks(chunk_results.value().second, chunk_results.value().first))) {
         return std::make_pair(DiagramCheckError::FAILURE, "insufficient feerate: does not improve feerate diagram");
     }
     return std::nullopt;

src/test/feefrac_tests.cpp

@@ -82,43 +82,4 @@ BOOST_AUTO_TEST_CASE(feefrac_operators)
 
 }
 
-BOOST_AUTO_TEST_CASE(build_diagram_test)
-{
-    FeeFrac p1{1000, 100};
-    FeeFrac empty{0, 0};
-    FeeFrac zero_fee{0, 1};
-    FeeFrac oversized_1{4611686000000, 4000000};
-    FeeFrac oversized_2{184467440000000, 100000};
-
-    // Diagram-building will reorder chunks
-    std::vector<FeeFrac> chunks;
-    chunks.push_back(p1);
-    chunks.push_back(zero_fee);
-    chunks.push_back(empty);
-    chunks.push_back(oversized_1);
-    chunks.push_back(oversized_2);
-
-    // Caller in charge of sorting chunks in case chunk size limit
-    // differs from cluster size limit
-    std::sort(chunks.begin(), chunks.end(), [](const FeeFrac& a, const FeeFrac& b) { return a > b; });
-
-    // Chunks are now sorted in reverse order (largest first)
-    BOOST_CHECK(chunks[0] == empty); // empty is considered "highest" fee
-    BOOST_CHECK(chunks[1] == oversized_2);
-    BOOST_CHECK(chunks[2] == oversized_1);
-    BOOST_CHECK(chunks[3] == p1);
-    BOOST_CHECK(chunks[4] == zero_fee);
-
-    std::vector<FeeFrac> generated_diagram{BuildDiagramFromChunks(chunks)};
-    BOOST_CHECK(generated_diagram.size() == 1 + chunks.size());
-
-    // Prepended with an empty, then the chunks summed in order as above
-    BOOST_CHECK(generated_diagram[0] == empty);
-    BOOST_CHECK(generated_diagram[1] == empty);
-    BOOST_CHECK(generated_diagram[2] == oversized_2);
-    BOOST_CHECK(generated_diagram[3] == oversized_2 + oversized_1);
-    BOOST_CHECK(generated_diagram[4] == oversized_2 + oversized_1 + p1);
-    BOOST_CHECK(generated_diagram[5] == oversized_2 + oversized_1 + p1 + zero_fee);
-}
-
 BOOST_AUTO_TEST_SUITE_END()

src/test/fuzz/feeratediagram.cpp

@@ -16,6 +16,20 @@
 
 namespace {
 
+/** Takes the pre-computed and topologically-valid chunks and generates a fee diagram which starts at FeeFrac of (0, 0) */
+std::vector<FeeFrac> BuildDiagramFromChunks(const Span<const FeeFrac> chunks)
+{
+    std::vector<FeeFrac> diagram;
+    diagram.reserve(chunks.size() + 1);
+
+    diagram.emplace_back(0, 0);
+    for (auto& chunk : chunks) {
+        diagram.emplace_back(diagram.back() + chunk);
+    }
+    return diagram;
+}
+
+
 /** Evaluate a diagram at a specific size, returning the fee as a fraction.
  *
  * Fees in diagram cannot exceed 2^32, as the returned evaluation could overflow
@@ -103,7 +117,7 @@ FUZZ_TARGET(build_and_compare_feerate_diagram)
     assert(diagram1.front() == empty);
     assert(diagram2.front() == empty);
 
-    auto real = CompareFeerateDiagram(diagram1, diagram2);
+    auto real = CompareChunks(chunks1, chunks2);
     auto sim = CompareDiagrams(diagram1, diagram2);
     assert(real == sim);
 

src/test/fuzz/rbf.cpp

@@ -82,17 +82,6 @@ FUZZ_TARGET(rbf, .init = initialize_rbf)
     }
 }
 
-void CheckDiagramConcave(std::vector<FeeFrac>& diagram)
-{
-    // Diagrams are in monotonically-decreasing feerate order.
-    FeeFrac last_chunk = diagram.front();
-    for (size_t i = 1; i<diagram.size(); ++i) {
-        FeeFrac next_chunk = diagram[i] - diagram[i-1];
-        assert(next_chunk <= last_chunk);
-        last_chunk = next_chunk;
-    }
-}
-
 FUZZ_TARGET(package_rbf, .init = initialize_package_rbf)
 {
     FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
@@ -107,7 +96,7 @@ FUZZ_TARGET(package_rbf, .init = initialize_package_rbf)
     std::vector<CTransaction> mempool_txs;
     size_t iter{0};
 
-    int64_t replacement_vsize = fuzzed_data_provider.ConsumeIntegralInRange<int64_t>(1, 1000000);
+    int32_t replacement_vsize = fuzzed_data_provider.ConsumeIntegralInRange<int32_t>(1, 1000000);
 
     // Keep track of the total vsize of CTxMemPoolEntry's being added to the mempool to avoid overflow
     // Add replacement_vsize since this is added to new diagram during RBF check
@@ -167,32 +156,33 @@ FUZZ_TARGET(package_rbf, .init = initialize_package_rbf)
         pool.CalculateDescendants(txiter, all_conflicts);
     }
 
-    // Calculate the feerate diagrams for a replacement.
+    // Calculate the chunks for a replacement.
     CAmount replacement_fees = ConsumeMoney(fuzzed_data_provider);
-    auto calc_results{pool.CalculateFeerateDiagramsForRBF(replacement_fees, replacement_vsize, direct_conflicts, all_conflicts)};
+    auto calc_results{pool.CalculateChunksForRBF(replacement_fees, replacement_vsize, direct_conflicts, all_conflicts)};
 
     if (calc_results.has_value()) {
-        // Sanity checks on the diagrams.
+        // Sanity checks on the chunks.
 
-        // Diagrams start at 0.
-        assert(calc_results->first.front().size == 0);
-        assert(calc_results->first.front().fee == 0);
-        assert(calc_results->second.front().size == 0);
-        assert(calc_results->second.front().fee == 0);
-
-        CheckDiagramConcave(calc_results->first);
-        CheckDiagramConcave(calc_results->second);
+        // Feerates are monotonically decreasing.
+        FeeFrac first_sum;
+        for (size_t i = 0; i < calc_results->first.size(); ++i) {
+            first_sum += calc_results->first[i];
+            if (i) assert(!(calc_results->first[i - 1] << calc_results->first[i]));
+        }
+        FeeFrac second_sum;
+        for (size_t i = 0; i < calc_results->second.size(); ++i) {
+            second_sum += calc_results->second[i];
+            if (i) assert(!(calc_results->second[i - 1] << calc_results->second[i]));
+        }
 
-        CAmount replaced_fee{0};
-        int64_t replaced_size{0};
+        FeeFrac replaced;
         for (auto txiter : all_conflicts) {
-            replaced_fee += txiter->GetModifiedFee();
-            replaced_size += txiter->GetTxSize();
+            replaced.fee += txiter->GetModifiedFee();
+            replaced.size += txiter->GetTxSize();
         }
-        // The total fee of the new diagram should be the total fee of the old
-        // diagram - replaced_fee + replacement_fees
-        assert(calc_results->first.back().fee - replaced_fee + replacement_fees == calc_results->second.back().fee);
-        assert(calc_results->first.back().size - replaced_size + replacement_vsize == calc_results->second.back().size);
+        // The total fee & size of the new diagram minus replaced fee & size should be the total
+        // fee & size of the old diagram minus replacement fee & size.
+        assert((first_sum - replaced) == (second_sum - FeeFrac{replacement_fees, replacement_vsize}));
     }
 
     // If internals report error, wrapper should too
@@ -201,10 +191,12 @@ FUZZ_TARGET(package_rbf, .init = initialize_package_rbf)
          assert(err_tuple.value().first == DiagramCheckError::UNCALCULABLE);
     } else {
         // Diagram check succeeded
+        auto old_sum = std::accumulate(calc_results->first.begin(), calc_results->first.end(), FeeFrac{});
+        auto new_sum = std::accumulate(calc_results->second.begin(), calc_results->second.end(), FeeFrac{});
         if (!err_tuple.has_value()) {
             // New diagram's final fee should always match or exceed old diagram's
-            assert(calc_results->first.back().fee <= calc_results->second.back().fee);
-        } else if (calc_results->first.back().fee > calc_results->second.back().fee) {
+            assert(old_sum.fee <= new_sum.fee);
+        } else if (old_sum.fee > new_sum.fee) {
             // Or it failed, and if old diagram had higher fees, it should be a failure
             assert(err_tuple.value().first == DiagramCheckError::FAILURE);
         }