Fix Overpayment Calculation (#6087)

- Adds additional unit tests to cover math calculations.
- Removes unused methods.

src/test/app/LendingHelpers_test.cpp

@@ -0,0 +1,642 @@
+#include <xrpl/beast/unit_test/suite.h>
+// DO NOT REMOVE
+#include <test/jtx.h>
+#include <test/jtx/Account.h>
+#include <test/jtx/amount.h>
+#include <test/jtx/mpt.h>
+
+#include <xrpld/app/misc/LendingHelpers.h>
+#include <xrpld/app/misc/LoadFeeTrack.h>
+#include <xrpld/app/tx/detail/Batch.h>
+#include <xrpld/app/tx/detail/LoanSet.h>
+
+#include <xrpl/beast/xor_shift_engine.h>
+#include <xrpl/protocol/SField.h>
+
+#include <string>
+#include <vector>
+
+namespace ripple {
+namespace test {
+
+class LendingHelpers_test : public beast::unit_test::suite
+{
+    void
+    testComputeRaisedRate()
+    {
+        using namespace jtx;
+        using namespace ripple::detail;
+        struct TestCase
+        {
+            std::string name;
+            Number periodicRate;
+            std::uint32_t paymentsRemaining;
+            Number expectedRaisedRate;
+        };
+
+        auto const testCases = std::vector<TestCase>{
+            {
+                .name = "Zero payments remaining",
+                .periodicRate = Number{5, -2},
+                .paymentsRemaining = 0,
+                .expectedRaisedRate = Number{1},  // (1 + r)^0 = 1
+            },
+            {
+                .name = "One payment remaining",
+                .periodicRate = Number{5, -2},
+                .paymentsRemaining = 1,
+                .expectedRaisedRate = Number{105, -2},
+            },  // 1.05^1
+            {
+                .name = "Multiple payments remaining",
+                .periodicRate = Number{5, -2},
+                .paymentsRemaining = 3,
+                .expectedRaisedRate = Number{1157625, -6},
+            },  // 1.05^3
+            {
+                .name = "Zero periodic rate",
+                .periodicRate = Number{0},
+                .paymentsRemaining = 5,
+                .expectedRaisedRate = Number{1},  // (1 + 0)^5 = 1
+            }};
+
+        for (auto const& tc : testCases)
+        {
+            testcase("computeRaisedRate: " + tc.name);
+
+            auto const computedRaisedRate =
+                computeRaisedRate(tc.periodicRate, tc.paymentsRemaining);
+            BEAST_EXPECTS(
+                computedRaisedRate == tc.expectedRaisedRate,
+                "Raised rate mismatch: expected " +
+                    to_string(tc.expectedRaisedRate) + ", got " +
+                    to_string(computedRaisedRate));
+        }
+    }
+
+    void
+    testComputePaymentFactor()
+    {
+        using namespace jtx;
+        using namespace ripple::detail;
+        struct TestCase
+        {
+            std::string name;
+            Number periodicRate;
+            std::uint32_t paymentsRemaining;
+            Number expectedPaymentFactor;
+        };
+
+        auto const testCases = std::vector<TestCase>{
+            {
+                .name = "Zero periodic rate",
+                .periodicRate = Number{0},
+                .paymentsRemaining = 4,
+                .expectedPaymentFactor = Number{25, -2},
+            },  // 1/4 = 0.25
+            {
+                .name = "One payment remaining",
+                .periodicRate = Number{5, -2},
+                .paymentsRemaining = 1,
+                .expectedPaymentFactor = Number{105, -2},
+            },  // 0.05/1 = 1.05
+            {
+                .name = "Multiple payments remaining",
+                .periodicRate = Number{5, -2},
+                .paymentsRemaining = 3,
+                .expectedPaymentFactor = Number{367208564631245, -15},
+            },  // from calc
+            {
+                .name = "Zero payments remaining",
+                .periodicRate = Number{5, -2},
+                .paymentsRemaining = 0,
+                .expectedPaymentFactor = Number{0},
+            }  // edge case
+        };
+
+        for (auto const& tc : testCases)
+        {
+            testcase("computePaymentFactor: " + tc.name);
+
+            auto const computedPaymentFactor =
+                computePaymentFactor(tc.periodicRate, tc.paymentsRemaining);
+            BEAST_EXPECTS(
+                computedPaymentFactor == tc.expectedPaymentFactor,
+                "Payment factor mismatch: expected " +
+                    to_string(tc.expectedPaymentFactor) + ", got " +
+                    to_string(computedPaymentFactor));
+        }
+    }
+
+    void
+    testLoanPeriodicPayment()
+    {
+        using namespace jtx;
+        using namespace ripple::detail;
+
+        struct TestCase
+        {
+            std::string name;
+            Number principalOutstanding;
+            Number periodicRate;
+            std::uint32_t paymentsRemaining;
+            Number expectedPeriodicPayment;
+        };
+
+        auto const testCases = std::vector<TestCase>{
+            {
+                .name = "Zero principal outstanding",
+                .principalOutstanding = Number{0},
+                .periodicRate = Number{5, -2},
+                .paymentsRemaining = 5,
+                .expectedPeriodicPayment = Number{0},
+            },
+            {
+                .name = "Zero payments remaining",
+                .principalOutstanding = Number{1'000},
+                .periodicRate = Number{5, -2},
+                .paymentsRemaining = 0,
+                .expectedPeriodicPayment = Number{0},
+            },
+            {
+                .name = "Zero periodic rate",
+                .principalOutstanding = Number{1'000},
+                .periodicRate = Number{0},
+                .paymentsRemaining = 4,
+                .expectedPeriodicPayment = Number{250},
+            },
+            {
+                .name = "Standard case",
+                .principalOutstanding = Number{1'000},
+                .periodicRate =
+                    loanPeriodicRate(TenthBips32(100'000), 30 * 24 * 60 * 60),
+                .paymentsRemaining = 3,
+                .expectedPeriodicPayment =
+                    Number{3895690663961231, -13},  // from calc
+            },
+        };
+
+        for (auto const& tc : testCases)
+        {
+            testcase("loanPeriodicPayment: " + tc.name);
+
+            auto const computedPeriodicPayment = loanPeriodicPayment(
+                tc.principalOutstanding, tc.periodicRate, tc.paymentsRemaining);
+            BEAST_EXPECTS(
+                computedPeriodicPayment == tc.expectedPeriodicPayment,
+                "Periodic payment mismatch: expected " +
+                    to_string(tc.expectedPeriodicPayment) + ", got " +
+                    to_string(computedPeriodicPayment));
+        }
+    }
+
+    void
+    testLoanPrincipalFromPeriodicPayment()
+    {
+        using namespace jtx;
+        using namespace ripple::detail;
+
+        struct TestCase
+        {
+            std::string name;
+            Number periodicPayment;
+            Number periodicRate;
+            std::uint32_t paymentsRemaining;
+            Number expectedPrincipalOutstanding;
+        };
+
+        auto const testCases = std::vector<TestCase>{
+            {
+                .name = "Zero periodic payment",
+                .periodicPayment = Number{0},
+                .periodicRate = Number{5, -2},
+                .paymentsRemaining = 5,
+                .expectedPrincipalOutstanding = Number{0},
+            },
+            {
+                .name = "Zero payments remaining",
+                .periodicPayment = Number{1'000},
+                .periodicRate = Number{5, -2},
+                .paymentsRemaining = 0,
+                .expectedPrincipalOutstanding = Number{0},
+            },
+            {
+                .name = "Zero periodic rate",
+                .periodicPayment = Number{250},
+                .periodicRate = Number{0},
+                .paymentsRemaining = 4,
+                .expectedPrincipalOutstanding = Number{1'000},
+            },
+            {
+                .name = "Standard case",
+                .periodicPayment = Number{3895690663961231, -13},  // from calc
+                .periodicRate =
+                    loanPeriodicRate(TenthBips32(100'000), 30 * 24 * 60 * 60),
+                .paymentsRemaining = 3,
+                .expectedPrincipalOutstanding = Number{1'000},
+            },
+        };
+
+        for (auto const& tc : testCases)
+        {
+            testcase("loanPrincipalFromPeriodicPayment: " + tc.name);
+
+            auto const computedPrincipalOutstanding =
+                loanPrincipalFromPeriodicPayment(
+                    tc.periodicPayment, tc.periodicRate, tc.paymentsRemaining);
+            BEAST_EXPECTS(
+                computedPrincipalOutstanding == tc.expectedPrincipalOutstanding,
+                "Principal outstanding mismatch: expected " +
+                    to_string(tc.expectedPrincipalOutstanding) + ", got " +
+                    to_string(computedPrincipalOutstanding));
+        }
+    }
+
+    void
+    testComputeOverpaymentComponents()
+    {
+        testcase("computeOverpaymentComponents");
+        using namespace jtx;
+        using namespace ripple::detail;
+
+        Account const issuer{"issuer"};
+        PrettyAsset const IOU = issuer["IOU"];
+        int32_t const loanScale = 1;
+        auto const overpayment = Number{1'000};
+        auto const overpaymentInterestRate = TenthBips32{10'000};  // 10%
+        auto const overpaymentFeeRate = TenthBips32{50'000};       // 50%
+        auto const managementFeeRate = TenthBips16{10'000};        // 10%
+
+        auto const expectedOverpaymentFee = Number{500};  // 50% of 1,000
+        auto const expectedOverpaymentInterestGross =
+            Number{100};  // 10% of 1,000
+        auto const expectedOverpaymentInterestNet =
+            Number{90};  // 100 - 10% of 100
+        auto const expectedOverpaymentManagementFee = Number{10};  // 10% of 100
+        auto const expectedPrincipalPortion = Number{400};  // 1,000 - 100 - 500
+
+        auto const components = detail::computeOverpaymentComponents(
+            IOU,
+            loanScale,
+            overpayment,
+            overpaymentInterestRate,
+            overpaymentFeeRate,
+            managementFeeRate);
+
+        BEAST_EXPECT(
+            components.untrackedManagementFee == expectedOverpaymentFee);
+
+        BEAST_EXPECT(
+            components.untrackedInterest == expectedOverpaymentInterestNet);
+        BEAST_EXPECT(
+            components.trackedManagementFeeDelta ==
+            expectedOverpaymentManagementFee);
+        BEAST_EXPECT(
+            components.trackedPrincipalDelta == expectedPrincipalPortion);
+        BEAST_EXPECT(
+            components.trackedManagementFeeDelta +
+                components.untrackedInterest ==
+            expectedOverpaymentInterestGross);
+
+        BEAST_EXPECT(
+            components.trackedManagementFeeDelta +
+                components.untrackedInterest +
+                components.trackedPrincipalDelta +
+                components.untrackedManagementFee ==
+            overpayment);
+    }
+
+    void
+    testComputeInterestAndFeeParts()
+    {
+        using namespace jtx;
+        using namespace ripple::detail;
+
+        struct TestCase
+        {
+            std::string name;
+            Number interest;
+            TenthBips16 managementFeeRate;
+            Number expectedInterestPart;
+            Number expectedFeePart;
+        };
+
+        Account const issuer{"issuer"};
+        PrettyAsset const IOU = issuer["IOU"];
+        std::int32_t const loanScale = 1;
+
+        auto const testCases = std::vector<TestCase>{
+            {.name = "Zero interest",
+             .interest = Number{0},
+             .managementFeeRate = TenthBips16{10'000},
+             .expectedInterestPart = Number{0},
+             .expectedFeePart = Number{0}},
+            {.name = "Zero fee rate",
+             .interest = Number{1'000},
+             .managementFeeRate = TenthBips16{0},
+             .expectedInterestPart = Number{1'000},
+             .expectedFeePart = Number{0}},
+            {.name = "10% fee rate",
+             .interest = Number{1'000},
+             .managementFeeRate = TenthBips16{10'000},
+             .expectedInterestPart = Number{900},
+             .expectedFeePart = Number{100}},
+        };
+
+        for (auto const& tc : testCases)
+        {
+            testcase("computeInterestAndFeeParts: " + tc.name);
+
+            auto const [computedInterestPart, computedFeePart] =
+                computeInterestAndFeeParts(
+                    IOU, tc.interest, tc.managementFeeRate, loanScale);
+            BEAST_EXPECTS(
+                computedInterestPart == tc.expectedInterestPart,
+                "Interest part mismatch: expected " +
+                    to_string(tc.expectedInterestPart) + ", got " +
+                    to_string(computedInterestPart));
+            BEAST_EXPECTS(
+                computedFeePart == tc.expectedFeePart,
+                "Fee part mismatch: expected " + to_string(tc.expectedFeePart) +
+                    ", got " + to_string(computedFeePart));
+        }
+    }
+
+    void
+    testLoanLatePaymentInterest()
+    {
+        using namespace jtx;
+        using namespace ripple::detail;
+        struct TestCase
+        {
+            std::string name;
+            Number principalOutstanding;
+            TenthBips32 lateInterestRate;
+            NetClock::time_point parentCloseTime;
+            std::uint32_t nextPaymentDueDate;
+            Number expectedLateInterest;
+        };
+
+        auto const testCases = std::vector<TestCase>{
+            {
+                .name = "On-time payment",
+                .principalOutstanding = Number{1'000},
+                .lateInterestRate = TenthBips32{10'000},  // 10%
+                .parentCloseTime =
+                    NetClock::time_point{NetClock::duration{3'000}},
+                .nextPaymentDueDate = 3'000,
+                .expectedLateInterest = Number{0},
+            },
+            {
+                .name = "Early payment",
+                .principalOutstanding = Number{1'000},
+                .lateInterestRate = TenthBips32{10'000},  // 10%
+                .parentCloseTime =
+                    NetClock::time_point{NetClock::duration{3'000}},
+                .nextPaymentDueDate = 4'000,
+                .expectedLateInterest = Number{0},
+            },
+            {
+                .name = "No principal outstanding",
+                .principalOutstanding = Number{0},
+                .lateInterestRate = TenthBips32{10'000},  // 10%
+                .parentCloseTime =
+                    NetClock::time_point{NetClock::duration{3'000}},
+                .nextPaymentDueDate = 2'000,
+                .expectedLateInterest = Number{0},
+            },
+            {
+                .name = "No late interest rate",
+                .principalOutstanding = Number{1'000},
+                .lateInterestRate = TenthBips32{0},  // 0%
+                .parentCloseTime =
+                    NetClock::time_point{NetClock::duration{3'000}},
+                .nextPaymentDueDate = 2'000,
+                .expectedLateInterest = Number{0},
+            },
+            {
+                .name = "Late payment",
+                .principalOutstanding = Number{1'000},
+                .lateInterestRate = TenthBips32{100'000},  // 100%
+                .parentCloseTime =
+                    NetClock::time_point{NetClock::duration{3'000}},
+                .nextPaymentDueDate = 2'000,
+                .expectedLateInterest =
+                    Number{3170979198376459, -17},  // from calc
+            },
+        };
+
+        for (auto const& tc : testCases)
+        {
+            testcase("loanLatePaymentInterest: " + tc.name);
+
+            auto const computedLateInterest = loanLatePaymentInterest(
+                tc.principalOutstanding,
+                tc.lateInterestRate,
+                tc.parentCloseTime,
+                tc.nextPaymentDueDate);
+            BEAST_EXPECTS(
+                computedLateInterest == tc.expectedLateInterest,
+                "Late interest mismatch: expected " +
+                    to_string(tc.expectedLateInterest) + ", got " +
+                    to_string(computedLateInterest));
+        }
+    }
+
+    void
+    testLoanAccruedInterest()
+    {
+        using namespace jtx;
+        using namespace ripple::detail;
+        struct TestCase
+        {
+            std::string name;
+            Number principalOutstanding;
+            Number periodicRate;
+            NetClock::time_point parentCloseTime;
+            std::uint32_t startDate;
+            std::uint32_t prevPaymentDate;
+            std::uint32_t paymentInterval;
+            Number expectedAccruedInterest;
+        };
+
+        auto const testCases = std::vector<TestCase>{
+            {
+                .name = "Zero principal outstanding",
+                .principalOutstanding = Number{0},
+                .periodicRate = Number{5, -2},
+                .parentCloseTime =
+                    NetClock::time_point{NetClock::duration{3'000}},
+                .startDate = 2'000,
+                .prevPaymentDate = 2'500,
+                .paymentInterval = 30 * 24 * 60 * 60,
+                .expectedAccruedInterest = Number{0},
+            },
+            {
+                .name = "Before start date",
+                .principalOutstanding = Number{1'000},
+                .periodicRate = Number{5, -2},
+                .parentCloseTime =
+                    NetClock::time_point{NetClock::duration{1'000}},
+                .startDate = 2'000,
+                .prevPaymentDate = 1'500,
+                .paymentInterval = 30 * 24 * 60 * 60,
+                .expectedAccruedInterest = Number{0},
+            },
+            {
+                .name = "Zero periodic rate",
+                .principalOutstanding = Number{1'000},
+                .periodicRate = Number{0},
+                .parentCloseTime =
+                    NetClock::time_point{NetClock::duration{3'000}},
+                .startDate = 2'000,
+                .prevPaymentDate = 2'500,
+                .paymentInterval = 30 * 24 * 60 * 60,
+                .expectedAccruedInterest = Number{0},
+            },
+            {
+                .name = "Zero payment interval",
+                .principalOutstanding = Number{1'000},
+                .periodicRate = Number{5, -2},
+                .parentCloseTime =
+                    NetClock::time_point{NetClock::duration{3'000}},
+                .startDate = 2'000,
+                .prevPaymentDate = 2'500,
+                .paymentInterval = 0,
+                .expectedAccruedInterest = Number{0},
+            },
+            {
+                .name = "Standard case",
+                .principalOutstanding = Number{1'000},
+                .periodicRate = Number{5, -2},
+                .parentCloseTime =
+                    NetClock::time_point{NetClock::duration{3'000}},
+                .startDate = 1'000,
+                .prevPaymentDate = 2'000,
+                .paymentInterval = 30 * 24 * 60 * 60,
+                .expectedAccruedInterest =
+                    Number{1929012345679012, -17},  // from calc
+            },
+        };
+
+        for (auto const& tc : testCases)
+        {
+            testcase("loanAccruedInterest: " + tc.name);
+
+            auto const computedAccruedInterest = loanAccruedInterest(
+                tc.principalOutstanding,
+                tc.periodicRate,
+                tc.parentCloseTime,
+                tc.startDate,
+                tc.prevPaymentDate,
+                tc.paymentInterval);
+            BEAST_EXPECTS(
+                computedAccruedInterest == tc.expectedAccruedInterest,
+                "Accrued interest mismatch: expected " +
+                    to_string(tc.expectedAccruedInterest) + ", got " +
+                    to_string(computedAccruedInterest));
+        }
+    }
+
+    // This test overlaps with testLoanAccruedInterest, the test cases only
+    // exercise the computeFullPaymentInterest parts unique to it.
+    void
+    testComputeFullPaymentInterest()
+    {
+        using namespace jtx;
+        using namespace ripple::detail;
+
+        struct TestCase
+        {
+            std::string name;
+            Number rawPrincipalOutstanding;
+            Number periodicRate;
+            NetClock::time_point parentCloseTime;
+            std::uint32_t paymentInterval;
+            std::uint32_t prevPaymentDate;
+            std::uint32_t startDate;
+            TenthBips32 closeInterestRate;
+            Number expectedFullPaymentInterest;
+        };
+
+        auto const testCases = std::vector<TestCase>{
+            {
+                .name = "Zero principal outstanding",
+                .rawPrincipalOutstanding = Number{0},
+                .periodicRate = Number{5, -2},
+                .parentCloseTime =
+                    NetClock::time_point{NetClock::duration{3'000}},
+                .paymentInterval = 30 * 24 * 60 * 60,
+                .prevPaymentDate = 2'000,
+                .startDate = 1'000,
+                .closeInterestRate = TenthBips32{10'000},
+                .expectedFullPaymentInterest = Number{0},
+            },
+            {
+                .name = "Zero close interest rate",
+                .rawPrincipalOutstanding = Number{1'000},
+                .periodicRate = Number{5, -2},
+                .parentCloseTime =
+                    NetClock::time_point{NetClock::duration{3'000}},
+                .paymentInterval = 30 * 24 * 60 * 60,
+                .prevPaymentDate = 2'000,
+                .startDate = 1'000,
+                .closeInterestRate = TenthBips32{0},
+                .expectedFullPaymentInterest =
+                    Number{1929012345679012, -17},  // from calc
+            },
+            {
+                .name = "Standard case",
+                .rawPrincipalOutstanding = Number{1'000},
+                .periodicRate = Number{5, -2},
+                .parentCloseTime =
+                    NetClock::time_point{NetClock::duration{3'000}},
+                .paymentInterval = 30 * 24 * 60 * 60,
+                .prevPaymentDate = 2'000,
+                .startDate = 1'000,
+                .closeInterestRate = TenthBips32{10'000},
+                .expectedFullPaymentInterest =
+                    Number{1000192901234568, -13},  // from calc
+            },
+        };
+
+        for (auto const& tc : testCases)
+        {
+            testcase("computeFullPaymentInterest: " + tc.name);
+
+            auto const computedFullPaymentInterest = computeFullPaymentInterest(
+                tc.rawPrincipalOutstanding,
+                tc.periodicRate,
+                tc.parentCloseTime,
+                tc.paymentInterval,
+                tc.prevPaymentDate,
+                tc.startDate,
+                tc.closeInterestRate);
+            BEAST_EXPECTS(
+                computedFullPaymentInterest == tc.expectedFullPaymentInterest,
+                "Full payment interest mismatch: expected " +
+                    to_string(tc.expectedFullPaymentInterest) + ", got " +
+                    to_string(computedFullPaymentInterest));
+        }
+    }
+
+public:
+    void
+    run() override
+    {
+        testComputeFullPaymentInterest();
+        testLoanAccruedInterest();
+        testLoanLatePaymentInterest();
+        testLoanPeriodicPayment();
+        testLoanPrincipalFromPeriodicPayment();
+        testComputeRaisedRate();
+        testComputePaymentFactor();
+        testComputeOverpaymentComponents();
+        testComputeInterestAndFeeParts();
+    }
+};
+
+BEAST_DEFINE_TESTSUITE(LendingHelpers, app, ripple);
+
+}  // namespace test
+}  // namespace ripple

src/test/app/Loan_test.cpp

@@ -2728,12 +2728,8 @@ protected:
                             broker.params.managementFeeRate);
 
                     BEAST_EXPECT(
-                        paymentComponents.trackedValueDelta ==
-                            roundedPeriodicPayment ||
-                        (paymentComponents.specialCase ==
-                             detail::PaymentSpecialCase::final &&
-                         paymentComponents.trackedValueDelta <
-                             roundedPeriodicPayment));
+                        paymentComponents.trackedValueDelta <=
+                        roundedPeriodicPayment);
 
                     ripple::LoanState const nextTrueState = computeRawLoanState(
                         state.periodicPayment,
@@ -6149,15 +6145,16 @@ protected:
         // Accrued + prepayment-penalty interest based on current periodic
         // schedule
         auto const fullPaymentInterest = computeFullPaymentInterest(
-            after.periodicPayment,
+            detail::loanPrincipalFromPeriodicPayment(
+                after.periodicPayment, periodicRate2, after.paymentRemaining),
             periodicRate2,
-            after.paymentRemaining,
             env.current()->parentCloseTime(),
             after.paymentInterval,
             after.previousPaymentDate,
             static_cast<std::uint32_t>(
                 after.startDate.time_since_epoch().count()),
             closeInterestRate);
+
         // Round to asset scale and split interest/fee parts
         auto const roundedInterest =
             roundToAsset(asset.raw(), fullPaymentInterest, after.loanScale);
@@ -6185,9 +6182,9 @@ protected:
         // window by clamping prevPaymentDate to 'now' for the full-pay path.
         auto const prevClamped = std::min(after.previousPaymentDate, nowSecs);
         auto const fullPaymentInterestClamped = computeFullPaymentInterest(
-            after.periodicPayment,
+            detail::loanPrincipalFromPeriodicPayment(
+                after.periodicPayment, periodicRate2, after.paymentRemaining),
             periodicRate2,
-            after.paymentRemaining,
             env.current()->parentCloseTime(),
             after.paymentInterval,
             prevClamped,

src/test/rpc/Feature_test.cpp

@@ -187,9 +187,9 @@ class Feature_test : public beast::unit_test::suite
         BEAST_EXPECTS(jrr[jss::status] == jss::success, "status");
         jrr.removeMember(jss::status);
         BEAST_EXPECT(jrr.size() == 1);
-        BEAST_EXPECT(jrr.isMember(
-            "740352F2412A9909880C23A559FCECEDA3BE2126FED62FC7660D6"
-            "28A06927F11"));
+        BEAST_EXPECT(
+            jrr.isMember("12523DF04B553A0B1AD74F42DDB741DE8DC06A03FC089A0EF197E"
+                         "2A87F1D8107"));
         auto feature = *(jrr.begin());
 
         BEAST_EXPECTS(feature[jss::name] == "fixAMMOverflowOffer", "name");

src/xrpld/app/misc/LendingHelpers.h

@@ -202,14 +202,6 @@ computeRawLoanState(
     std::uint32_t const paymentRemaining,
     TenthBips32 const managementFeeRate);
 
-LoanState
-computeRawLoanState(
-    Number const& periodicPayment,
-    TenthBips32 interestRate,
-    std::uint32_t paymentInterval,
-    std::uint32_t const paymentRemaining,
-    TenthBips32 const managementFeeRate);
-
 // Constructs a valid LoanState object from arbitrary inputs
 LoanState
 constructLoanState(
@@ -239,17 +231,6 @@ computeFullPaymentInterest(
     std::uint32_t startDate,
     TenthBips32 closeInterestRate);
 
-Number
-computeFullPaymentInterest(
-    Number const& periodicPayment,
-    Number const& periodicRate,
-    std::uint32_t paymentRemaining,
-    NetClock::time_point parentCloseTime,
-    std::uint32_t paymentInterval,
-    std::uint32_t prevPaymentDate,
-    std::uint32_t startDate,
-    TenthBips32 closeInterestRate);
-
 namespace detail {
 // These classes and functions should only be accessed by LendingHelper
 // functions and unit tests
@@ -387,6 +368,58 @@ struct LoanStateDeltas
     nonNegative();
 };
 
+Number
+computeRaisedRate(Number const& periodicRate, std::uint32_t paymentsRemaining);
+
+Number
+computePaymentFactor(
+    Number const& periodicRate,
+    std::uint32_t paymentsRemaining);
+
+std::pair<Number, Number>
+computeInterestAndFeeParts(
+    Asset const& asset,
+    Number const& interest,
+    TenthBips16 managementFeeRate,
+    std::int32_t loanScale);
+
+Number
+loanPeriodicPayment(
+    Number const& principalOutstanding,
+    Number const& periodicRate,
+    std::uint32_t paymentsRemaining);
+
+Number
+loanPrincipalFromPeriodicPayment(
+    Number const& periodicPayment,
+    Number const& periodicRate,
+    std::uint32_t paymentsRemaining);
+
+Number
+loanLatePaymentInterest(
+    Number const& principalOutstanding,
+    TenthBips32 lateInterestRate,
+    NetClock::time_point parentCloseTime,
+    std::uint32_t nextPaymentDueDate);
+
+Number
+loanAccruedInterest(
+    Number const& principalOutstanding,
+    Number const& periodicRate,
+    NetClock::time_point parentCloseTime,
+    std::uint32_t startDate,
+    std::uint32_t prevPaymentDate,
+    std::uint32_t paymentInterval);
+
+ExtendedPaymentComponents
+computeOverpaymentComponents(
+    Asset const& asset,
+    int32_t const loanScale,
+    Number const& overpayment,
+    TenthBips32 const overpaymentInterestRate,
+    TenthBips32 const overpaymentFeeRate,
+    TenthBips16 const managementFeeRate);
+
 PaymentComponents
 computePaymentComponents(
     Asset const& asset,

src/xrpld/app/misc/detail/LendingHelpers.cpp

@@ -100,6 +100,9 @@ computePaymentFactor(
     Number const& periodicRate,
     std::uint32_t paymentsRemaining)
 {
+    if (paymentsRemaining == 0)
+        return numZero;
+
     // For zero interest, payment factor is simply 1/paymentsRemaining
     if (periodicRate == beast::zero)
         return Number{1} / paymentsRemaining;
@@ -132,27 +135,6 @@ loanPeriodicPayment(
         computePaymentFactor(periodicRate, paymentsRemaining);
 }
 
-/* Calculates the periodic payment amount from annualized interest rate.
- * Converts the annual rate to periodic rate before computing payment.
- *
- * Equation (7) from XLS-66 spec, Section A-2 Equation Glossary
- */
-Number
-loanPeriodicPayment(
-    Number const& principalOutstanding,
-    TenthBips32 interestRate,
-    std::uint32_t paymentInterval,
-    std::uint32_t paymentsRemaining)
-{
-    if (principalOutstanding == 0 || paymentsRemaining == 0)
-        return 0;
-
-    Number const periodicRate = loanPeriodicRate(interestRate, paymentInterval);
-
-    return loanPeriodicPayment(
-        principalOutstanding, periodicRate, paymentsRemaining);
-}
-
 /* Reverse-calculates principal from periodic payment amount.
  * Used to determine theoretical principal at any point in the schedule.
  *
@@ -164,6 +146,9 @@ loanPrincipalFromPeriodicPayment(
     Number const& periodicRate,
     std::uint32_t paymentsRemaining)
 {
+    if (paymentsRemaining == 0)
+        return numZero;
+
     if (periodicRate == 0)
         return periodicPayment * paymentsRemaining;
 
@@ -171,21 +156,6 @@ loanPrincipalFromPeriodicPayment(
         computePaymentFactor(periodicRate, paymentsRemaining);
 }
 
-/* Splits gross interest into net interest (to vault) and management fee (to
- * broker). Returns pair of (net interest, management fee).
- *
- * Equation (33) from XLS-66 spec, Section A-2 Equation Glossary
- */
-std::pair<Number, Number>
-computeInterestAndFeeParts(
-    Number const& interest,
-    TenthBips16 managementFeeRate)
-{
-    auto const fee = tenthBipsOfValue(interest, managementFeeRate);
-
-    return std::make_pair(interest - fee, fee);
-}
-
 /*
  * Computes the interest and management fee parts from interest amount.
  *
@@ -216,6 +186,12 @@ loanLatePaymentInterest(
     NetClock::time_point parentCloseTime,
     std::uint32_t nextPaymentDueDate)
 {
+    if (principalOutstanding == beast::zero)
+        return numZero;
+
+    if (lateInterestRate == TenthBips32{0})
+        return numZero;
+
     auto const now = parentCloseTime.time_since_epoch().count();
 
     // If the payment is not late by any amount of time, then there's no late
@@ -248,6 +224,9 @@ loanAccruedInterest(
     if (periodicRate == beast::zero)
         return numZero;
 
+    if (paymentInterval == 0)
+        return numZero;
+
     auto const lastPaymentDate = std::max(prevPaymentDate, startDate);
     auto const now = parentCloseTime.time_since_epoch().count();
 
@@ -1095,23 +1074,6 @@ computePaymentComponents(
             "ripple::detail::computePaymentComponents",
             "excess non-negative");
     };
-    auto giveTo =
-        [](Number& component, Number& shortage, Number const& maximum) {
-            if (shortage > beast::zero)
-            {
-                // Put as much of the shortage as we can into the provided part
-                // and the total
-                auto part = std::min(maximum - component, shortage);
-                component += part;
-                shortage -= part;
-            }
-            // If the shortage goes negative, we put too much, which should be
-            // impossible
-            XRPL_ASSERT_PARTS(
-                shortage >= beast::zero,
-                "ripple::detail::computePaymentComponents",
-                "excess non-negative");
-        };
     // Helper to reduce deltas when they collectively exceed a limit.
     // Order matters: we prefer to reduce interest first (most flexible),
     // then management fee, then principal (least flexible).
@@ -1121,19 +1083,6 @@ computePaymentComponents(
         takeFrom(deltas.managementFee, excess);
         takeFrom(deltas.principal, excess);
     };
-    // Helper to increase deltas when they collectively do not reach an
-    // expected value.
-    // Order matters: we prefer to increase interest first (most flexible),
-    // then management fee, then principal (least flexible).
-    auto addressShortage = [&giveTo](
-                               LoanDeltas& deltas,
-                               Number& shortage,
-                               LoanState const& current) {
-        giveTo(deltas.interestDueDelta, shortage, current.interestDue);
-        giveTo(
-            deltas.managementFeeDueDelta, shortage, current.managementFeeDue);
-        giveTo(deltas.principalDelta, shortage, current.principalOutstanding);
-    };
 
     // Check if deltas exceed the total outstanding value. This should never
     // happen due to earlier caps, but handle it defensively.
@@ -1165,19 +1114,12 @@ computePaymentComponents(
         addressExcess(deltas, excess);
         shortage = -excess;
     }
-    else if (shortage > beast::zero && totalOverpayment < beast::zero)
-    {
-        // If there's a shortage, and there's room in the loan itself, we can
-        // top up the parts to make the payment correct.
-        shortage = std::min(-totalOverpayment, shortage);
-        addressShortage(deltas, shortage, currentLedgerState);
-    }
 
     // At this point, shortage >= 0 means we're paying less than the full
     // periodic payment (due to rounding or component caps).
-    // shortage < 0 means mean we're trying to pay more than allowed (bug).
+    // shortage < 0 would mean we're trying to pay more than allowed (bug).
     XRPL_ASSERT_PARTS(
-        shortage == beast::zero,
+        shortage >= beast::zero,
         "ripple::detail::computePaymentComponents",
         "no shortage or excess");
 
@@ -1262,17 +1204,12 @@ computeOverpaymentComponents(
     // This interest doesn't follow the normal amortization schedule - it's
     // a one-time charge for paying early.
     // Equation (20) and (21) from XLS-66 spec, Section A-2 Equation Glossary
-    auto const [rawOverpaymentInterest, _] = [&]() {
-        Number const interest =
-            tenthBipsOfValue(overpayment, overpaymentInterestRate);
-        return detail::computeInterestAndFeeParts(interest, managementFeeRate);
-    }();
-
-    // Round the penalty interest components to the loan scale
     auto const [roundedOverpaymentInterest, roundedOverpaymentManagementFee] =
         [&]() {
-            Number const interest =
-                roundToAsset(asset, rawOverpaymentInterest, loanScale);
+            auto const interest = roundToAsset(
+                asset,
+                tenthBipsOfValue(overpayment, overpaymentInterestRate),
+                loanScale);
             return detail::computeInterestAndFeeParts(
                 asset, interest, managementFeeRate, loanScale);
         }();
@@ -1466,31 +1403,6 @@ computeFullPaymentInterest(
     return accruedInterest + prepaymentPenalty;
 }
 
-Number
-computeFullPaymentInterest(
-    Number const& periodicPayment,
-    Number const& periodicRate,
-    std::uint32_t paymentRemaining,
-    NetClock::time_point parentCloseTime,
-    std::uint32_t paymentInterval,
-    std::uint32_t prevPaymentDate,
-    std::uint32_t startDate,
-    TenthBips32 closeInterestRate)
-{
-    Number const rawPrincipalOutstanding =
-        detail::loanPrincipalFromPeriodicPayment(
-            periodicPayment, periodicRate, paymentRemaining);
-
-    return computeFullPaymentInterest(
-        rawPrincipalOutstanding,
-        periodicRate,
-        parentCloseTime,
-        paymentInterval,
-        prevPaymentDate,
-        startDate,
-        closeInterestRate);
-}
-
 /* Calculates the theoretical loan state at maximum precision for a given point
  * in the amortization schedule.
  *
@@ -1552,21 +1464,6 @@ computeRawLoanState(
         .managementFeeDue = rawManagementFeeOutstanding};
 };
 
-LoanState
-computeRawLoanState(
-    Number const& periodicPayment,
-    TenthBips32 interestRate,
-    std::uint32_t paymentInterval,
-    std::uint32_t const paymentRemaining,
-    TenthBips32 const managementFeeRate)
-{
-    return computeRawLoanState(
-        periodicPayment,
-        loanPeriodicRate(interestRate, paymentInterval),
-        paymentRemaining,
-        managementFeeRate);
-}
-
 /* Constructs a LoanState from rounded Loan ledger object values.
  *
  * This function creates a LoanState structure from the three tracked values

src/xrpld/app/tx/detail/LoanBrokerDelete.cpp

@@ -67,7 +67,7 @@ LoanBrokerDelete::preclaim(PreclaimContext const& ctx)
             JLOG(ctx.j.warn()) << "LoanBrokerDelete: Debt total is "
                                << debtTotal << ", which rounds to " << rounded;
             return tecHAS_OBLIGATIONS;
-            // LCOV_EXCL_START
+            // LCOV_EXCL_STOP
         }
     }