Add canonical "scale" computation to Number (#6246)

* Add canonical "scale" computation to Number

- Requires a template for STAmount and Asset.
- Update tests and computeMinScale from #6217 to use scale.
- Convert a few other places to use "scale" correctly.

* ValidVault tracks scale of original operands alongside deltas

* Update src/xrpld/app/tx/detail/InvariantCheck.cpp

Co-authored-by: Vito Tumas <5780819+Tapanito@users.noreply.github.com>

* Change ValidVault::DeltaInfo::scale to an optional

* Change computeMinScale to use a vector instead of an initializer_list

* Fix compile errors

---------

Co-authored-by: Vito Tumas <5780819+Tapanito@users.noreply.github.com>

include/xrpl/basics/Number.h

@@ -110,6 +110,10 @@ template <class T>
 concept Integral64 =
     std::is_same_v<T, std::int64_t> || std::is_same_v<T, std::uint64_t>;
 
+template <class STAmount, class Asset>
+concept CanUseAsScale = requires(Asset a, Number n) { STAmount(a, n); } &&
+    requires(STAmount s) { s.exponent(); };
+
 /** Number is a floating point type that can represent a wide range of values.
  *
  * It can represent all values that can be represented by an STAmount -
@@ -269,6 +273,26 @@ public:
     constexpr int
     exponent() const noexcept;
 
+    /** Get the scale of this Number for the given asset.
+     *
+     * "scale" is similar to "exponent", but from the perspective of STAmount,
+     * which has different rules for determining the exponent than Number.
+     *
+     * Because Number does not have access to STAmount or Asset, this function
+     * is implemented as a template, with the expectation that it will only be
+     * used by those types. Any types that fit the requirements will work,
+     * though, if there's a need.
+     *
+     * @tparam STAmount The STAmount type.
+     * @tparam Asset The Asset type.
+     * @param asset The asset to use for determining the scale.
+     * @return The scale of this Number for the given asset.
+     */
+    template <class STAmount, class Asset>
+    int
+    scale(Asset const& asset) const
+        requires CanUseAsScale<STAmount, Asset>;
+
     constexpr Number
     operator+() const noexcept;
     constexpr Number
@@ -603,6 +627,14 @@ Number::exponent() const noexcept
     return e;
 }
 
+template <class STAmount, class Asset>
+int
+Number::scale(Asset const& asset) const
+    requires CanUseAsScale<STAmount, Asset>
+{
+    return STAmount{asset, *this}.exponent();
+}
+
 inline constexpr Number
 Number::operator+() const noexcept
 {

include/xrpl/protocol/STAmount.h

@@ -43,8 +43,8 @@ private:
 public:
     using value_type = STAmount;
 
-    static int const cMinOffset = -96;
-    static int const cMaxOffset = 80;
+    static int constexpr cMinOffset = -96;
+    static int constexpr cMaxOffset = 80;
 
     // Maximum native value supported by the code
     constexpr static std::uint64_t cMinValue = 1'000'000'000'000'000ull;

src/test/app/Invariants_test.cpp

@@ -4,6 +4,7 @@
 
 #include <xrpld/app/tx/apply.h>
 #include <xrpld/app/tx/detail/ApplyContext.h>
+#include <xrpld/app/tx/detail/InvariantCheck.h>
 
 #include <xrpl/beast/unit_test/suite.h>
 #include <xrpl/beast/utility/Journal.h>
@@ -3891,6 +3892,140 @@ class Invariants_test : public beast::unit_test::suite
             precloseMpt);
     }
 
+    void
+    testVaultComputeMinScale()
+    {
+        using namespace jtx;
+
+        Account const issuer{"issuer"};
+        PrettyAsset const vaultAsset = issuer["IOU"];
+
+        struct TestCase
+        {
+            std::string name;
+            std::int32_t expectedMinScale;
+            std::vector<ValidVault::DeltaInfo> values;
+        };
+
+        NumberMantissaScaleGuard g{MantissaRange::large};
+
+        auto makeDelta =
+            [&vaultAsset](Number const& n) -> ValidVault::DeltaInfo {
+            return {n, n.scale<STAmount>(vaultAsset.raw())};
+        };
+
+        auto const testCases = std::vector<TestCase>{
+            {
+                .name = "No values",
+                .expectedMinScale = 0,
+                .values = {},
+            },
+            {
+                .name = "Mixed integer and Number values",
+                .expectedMinScale = -15,
+                .values =
+                    {makeDelta(1), makeDelta(-1), makeDelta(Number{10, -1})},
+            },
+            {
+                .name = "Mixed scales",
+                .expectedMinScale = -17,
+                .values =
+                    {makeDelta(Number{1, -2}),
+                     makeDelta(Number{5, -3}),
+                     makeDelta(Number{3, -2})},
+            },
+            {
+                .name = "Equal scales",
+                .expectedMinScale = -16,
+                .values =
+                    {makeDelta(Number{1, -1}),
+                     makeDelta(Number{5, -1}),
+                     makeDelta(Number{1, -1})},
+            },
+            {
+                .name = "Mixed mantissa sizes",
+                .expectedMinScale = -12,
+                .values =
+                    {makeDelta(Number{1}),
+                     makeDelta(Number{1234, -3}),
+                     makeDelta(Number{12345, -6}),
+                     makeDelta(Number{123, 1})},
+            },
+        };
+
+        for (auto const& tc : testCases)
+        {
+            testcase("vault computeMinScale: " + tc.name);
+
+            auto const actualScale =
+                ValidVault::computeMinScale(vaultAsset, tc.values);
+
+            BEAST_EXPECTS(
+                actualScale == tc.expectedMinScale,
+                "expected: " + std::to_string(tc.expectedMinScale) +
+                    ", actual: " + std::to_string(actualScale));
+            for (auto const& num : tc.values)
+            {
+                // None of these scales are far enough apart that rounding the
+                // values would lose information, so check that the rounded
+                // value matches the original.
+                auto const actualRounded =
+                    roundToAsset(vaultAsset, num.delta, actualScale);
+                BEAST_EXPECTS(
+                    actualRounded == num.delta,
+                    "number " + to_string(num.delta) + " rounded to scale " +
+                        std::to_string(actualScale) + " is " +
+                        to_string(actualRounded));
+            }
+        }
+
+        auto const testCases2 = std::vector<TestCase>{
+            {
+                .name = "False equivalence",
+                .expectedMinScale = -15,
+                .values =
+                    {
+                        makeDelta(Number{1234567890123456789, -18}),
+                        makeDelta(Number{12345, -4}),
+                        makeDelta(Number{1}),
+                    },
+            },
+        };
+
+        // Unlike the first set of test cases, the values in these test could
+        // look equivalent if using the wrong scale.
+        for (auto const& tc : testCases2)
+        {
+            testcase("vault computeMinScale: " + tc.name);
+
+            auto const actualScale =
+                ValidVault::computeMinScale(vaultAsset, tc.values);
+
+            BEAST_EXPECTS(
+                actualScale == tc.expectedMinScale,
+                "expected: " + std::to_string(tc.expectedMinScale) +
+                    ", actual: " + std::to_string(actualScale));
+            std::optional<Number> first;
+            Number firstRounded;
+            for (auto const& num : tc.values)
+            {
+                if (!first)
+                {
+                    first = num.delta;
+                    firstRounded =
+                        roundToAsset(vaultAsset, num.delta, actualScale);
+                    continue;
+                }
+                auto const numRounded =
+                    roundToAsset(vaultAsset, num.delta, actualScale);
+                BEAST_EXPECTS(
+                    numRounded != firstRounded,
+                    "at a scale of " + std::to_string(actualScale) + " " +
+                        to_string(num.delta) + " == " + to_string(*first));
+            }
+        }
+    }
+
 public:
     void
     run() override
@@ -3914,6 +4049,7 @@ public:
         testValidPseudoAccounts();
         testValidLoanBroker();
         testVault();
+        testVaultComputeMinScale();
     }
 };
 

src/xrpld/app/misc/LendingHelpers.h

@@ -176,8 +176,7 @@ getAssetsTotalScale(SLE::const_ref vaultSle)
 {
     if (!vaultSle)
         return Number::minExponent - 1;  // LCOV_EXCL_LINE
-    return STAmount{vaultSle->at(sfAsset), vaultSle->at(sfAssetsTotal)}
-        .exponent();
+    return vaultSle->at(sfAssetsTotal).scale<STAmount>(vaultSle->at(sfAsset));
 }
 
 TER

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

@@ -2664,8 +2664,13 @@ ValidVault::visitEntry(
     // Number balanceDelta will capture the difference (delta) between "before"
     // state (zero if created) and "after" state (zero if destroyed), so the
     // invariants can validate that the change in account balances matches the
-    // change in vault balances, stored to deltas_ at the end of this function.
-    Number balanceDelta{};
+    // balanceDelta captures the difference (delta) between "before"
+    // state (zero if created) and "after" state (zero if destroyed), and
+    // preserves value scale (exponent) to round values to the same scale during
+    // validation. It is used to validate that the change in account
+    // balances matches the change in vault balances, stored to deltas_ at the
+    // end of this function.
+    DeltaInfo balanceDelta{numZero, std::nullopt};
 
     std::int8_t sign = 0;
     if (before)
@@ -2679,20 +2684,35 @@ ValidVault::visitEntry(
                 // At this moment we have no way of telling if this object holds
                 // vault shares or something else. Save it for finalize.
                 beforeMPTs_.push_back(Shares::make(*before));
-                balanceDelta = static_cast<std::int64_t>(
+                balanceDelta.delta = static_cast<std::int64_t>(
                     before->getFieldU64(sfOutstandingAmount));
+                // MPTs are ints, so the scale is always 0.
+                balanceDelta.scale = 0;
                 sign = 1;
                 break;
             case ltMPTOKEN:
-                balanceDelta =
+                balanceDelta.delta =
                     static_cast<std::int64_t>(before->getFieldU64(sfMPTAmount));
+                // MPTs are ints, so the scale is always 0.
+                balanceDelta.scale = 0;
                 sign = -1;
                 break;
             case ltACCOUNT_ROOT:
-            case ltRIPPLE_STATE:
-                balanceDelta = before->getFieldAmount(sfBalance);
+                balanceDelta.delta = before->getFieldAmount(sfBalance);
+                // Account balance is XRP, which is an int, so the scale is
+                // always 0.
+                balanceDelta.scale = 0;
                 sign = -1;
                 break;
+            case ltRIPPLE_STATE: {
+                auto const amount = before->getFieldAmount(sfBalance);
+                balanceDelta.delta = amount;
+                // Trust Line balances are STAmounts, so we can use the exponent
+                // directly to get the scale.
+                balanceDelta.scale = amount.exponent();
+                sign = -1;
+                break;
+            }
             default:;
         }
     }
@@ -2708,21 +2728,36 @@ ValidVault::visitEntry(
                 // At this moment we have no way of telling if this object holds
                 // vault shares or something else. Save it for finalize.
                 afterMPTs_.push_back(Shares::make(*after));
-                balanceDelta -= Number(
-                    static_cast<std::int64_t>(
-                        after->getFieldU64(sfOutstandingAmount)));
+                balanceDelta.delta -= Number(static_cast<std::int64_t>(
+                    after->getFieldU64(sfOutstandingAmount)));
+                // MPTs are ints, so the scale is always 0.
+                balanceDelta.scale = 0;
                 sign = 1;
                 break;
             case ltMPTOKEN:
-                balanceDelta -= Number(
+                balanceDelta.delta -= Number(
                     static_cast<std::int64_t>(after->getFieldU64(sfMPTAmount)));
+                // MPTs are ints, so the scale is always 0.
+                balanceDelta.scale = 0;
                 sign = -1;
                 break;
             case ltACCOUNT_ROOT:
-            case ltRIPPLE_STATE:
-                balanceDelta -= Number(after->getFieldAmount(sfBalance));
+                balanceDelta.delta -= Number(after->getFieldAmount(sfBalance));
+                // Account balance is XRP, which is an int, so the scale is
+                // always 0.
+                balanceDelta.scale = 0;
                 sign = -1;
                 break;
+            case ltRIPPLE_STATE: {
+                auto const amount = after->getFieldAmount(sfBalance);
+                balanceDelta.delta -= Number(amount);
+                // Trust Line balances are STAmounts, so we can use the exponent
+                // directly to get the scale.
+                if (amount.exponent() > balanceDelta.scale)
+                    balanceDelta.scale = amount.exponent();
+                sign = -1;
+                break;
+            }
             default:;
         }
     }
@@ -2734,7 +2769,14 @@ ValidVault::visitEntry(
     // transferred to the account. We intentionally do not compare balanceDelta
     // against zero, to avoid missing such updates.
     if (sign != 0)
-        deltas_[key] = balanceDelta * sign;
+    {
+        XRPL_ASSERT_PARTS(
+            balanceDelta.scale,
+            "xrpl::ValidVault::visitEntry",
+            "scale initialized");
+        balanceDelta.delta *= sign;
+        deltas_[key] = balanceDelta;
+    }
 }
 
 bool
@@ -3014,13 +3056,15 @@ ValidVault::finalize(
     }
 
     auto const& vaultAsset = afterVault.asset;
-    auto const deltaAssets = [&](AccountID const& id) -> std::optional<Number> {
+    auto const deltaAssets =
+        [&](AccountID const& id) -> std::optional<DeltaInfo> {
         auto const get =  //
-            [&](auto const& it, std::int8_t sign = 1) -> std::optional<Number> {
+            [&](auto const& it,
+                std::int8_t sign = 1) -> std::optional<DeltaInfo> {
             if (it == deltas_.end())
                 return std::nullopt;
 
-            return it->second * sign;
+            return DeltaInfo{it->second.delta * sign, it->second.scale};
         };
 
         return std::visit(
@@ -3041,7 +3085,7 @@ ValidVault::finalize(
             },
             vaultAsset.value());
     };
-    auto const deltaAssetsTxAccount = [&]() -> std::optional<Number> {
+    auto const deltaAssetsTxAccount = [&]() -> std::optional<DeltaInfo> {
         auto ret = deltaAssets(tx[sfAccount]);
         // Nothing returned or not XRP transaction
         if (!ret.has_value() || !vaultAsset.native())
@@ -3052,13 +3096,14 @@ ValidVault::finalize(
             delegate.has_value() && *delegate != tx[sfAccount])
             return ret;
 
-        *ret += fee.drops();
-        if (*ret == zero)
+        ret->delta += fee.drops();
+        if (ret->delta == zero)
             return std::nullopt;
 
         return ret;
     };
-    auto const deltaShares = [&](AccountID const& id) -> std::optional<Number> {
+    auto const deltaShares =
+        [&](AccountID const& id) -> std::optional<DeltaInfo> {
         auto const it = [&]() {
             if (id == afterVault.pseudoId)
                 return deltas_.find(
@@ -3066,7 +3111,7 @@ ValidVault::finalize(
             return deltas_.find(keylet::mptoken(afterVault.shareMPTID, id).key);
         }();
 
-        return it != deltas_.end() ? std::optional<Number>(it->second)
+        return it != deltas_.end() ? std::optional<DeltaInfo>(it->second)
                                    : std::nullopt;
     };
 
@@ -3074,15 +3119,6 @@ ValidVault::finalize(
         return vault.assetsAvailable == 0 && vault.assetsTotal == 0;
     };
 
-    auto const withinDistance = [&](Number const& num1,
-                                    Number const& num2) -> bool {
-        if (vaultAsset.integral())
-            return num1 == num2;
-        // The exponent was set experimentally, based on whether
-        // Loan_test::testWithdrawReflectsUnrealizedLoss unit test fail
-        return withinRelativeDistance(num1, num2, Number{1, -13});
-    };
-
     // Technically this does not need to be a lambda, but it's more
     // convenient thanks to early "return false"; the not-so-nice
     // alternatives are several layers of nested if/else or more complex
@@ -3216,8 +3252,32 @@ ValidVault::finalize(
                     return false;  // That's all we can do
                 }
 
-                auto const vaultDeltaAssets = *maybeVaultDeltaAssets;
-                if (vaultDeltaAssets > tx[sfAmount])
+                // Get the coarsest scale to round calculations to
+                DeltaInfo totalDelta{
+                    afterVault.assetsTotal - beforeVault.assetsTotal,
+                    std::max(
+                        afterVault.assetsTotal.scale<STAmount>(vaultAsset),
+                        beforeVault.assetsTotal.scale<STAmount>(vaultAsset))};
+                DeltaInfo availableDelta{
+                    afterVault.assetsAvailable - beforeVault.assetsAvailable,
+                    std::max(
+                        afterVault.assetsAvailable.scale<STAmount>(vaultAsset),
+                        beforeVault.assetsAvailable.scale<STAmount>(
+                            vaultAsset))};
+                auto const minScale = computeMinScale(
+                    vaultAsset,
+                    {
+                        *maybeVaultDeltaAssets,
+                        totalDelta,
+                        availableDelta,
+                    });
+
+                auto const vaultDeltaAssets = roundToAsset(
+                    vaultAsset, maybeVaultDeltaAssets->delta, minScale);
+                auto const txAmount =
+                    roundToAsset(vaultAsset, tx[sfAmount], minScale);
+
+                if (vaultDeltaAssets > txAmount)
                 {
                     JLOG(j.fatal()) <<  //
                         "Invariant failed: deposit must not change vault "
@@ -3250,7 +3310,14 @@ ValidVault::finalize(
                             "balance";
                         return false;
                     }
-                    auto const accountDeltaAssets = *maybeAccDeltaAssets;
+                    auto const localMinScale = std::max(
+                        minScale,
+                        computeMinScale(vaultAsset, {*maybeAccDeltaAssets}));
+
+                    auto const accountDeltaAssets = roundToAsset(
+                        vaultAsset, maybeAccDeltaAssets->delta, localMinScale);
+                    auto const localVaultDeltaAssets = roundToAsset(
+                        vaultAsset, vaultDeltaAssets, localMinScale);
 
                     if (accountDeltaAssets >= zero)
                     {
@@ -3260,8 +3327,7 @@ ValidVault::finalize(
                         result = false;
                     }
 
-                    if (!withinDistance(
-                            vaultDeltaAssets * -1, accountDeltaAssets))
+                    if (localVaultDeltaAssets * -1 != accountDeltaAssets)
                     {
                         JLOG(j.fatal()) <<  //
                             "Invariant failed: deposit must change vault and "
@@ -3289,7 +3355,7 @@ ValidVault::finalize(
                 }
                 // We don't need to round shares, they are integral MPT
                 auto const& accountDeltaShares = *maybeAccDeltaShares;
-                if (accountDeltaShares <= zero)
+                if (accountDeltaShares.delta <= zero)
                 {
                     JLOG(j.fatal()) <<  //
                         "Invariant failed: deposit must increase depositor "
@@ -3299,7 +3365,8 @@ ValidVault::finalize(
 
                 auto const maybeVaultDeltaShares =
                     deltaShares(afterVault.pseudoId);
-                if (!maybeVaultDeltaShares || *maybeVaultDeltaShares == zero)
+                if (!maybeVaultDeltaShares ||
+                    maybeVaultDeltaShares->delta == zero)
                 {
                     JLOG(j.fatal()) <<  //
                         "Invariant failed: deposit must change vault shares";
@@ -3308,7 +3375,7 @@ ValidVault::finalize(
 
                 // We don't need to round shares, they are integral MPT
                 auto const& vaultDeltaShares = *maybeVaultDeltaShares;
-                if (vaultDeltaShares * -1 != accountDeltaShares)
+                if (vaultDeltaShares.delta * -1 != accountDeltaShares.delta)
                 {
                     JLOG(j.fatal()) <<  //
                         "Invariant failed: deposit must change depositor and "
@@ -3316,18 +3383,22 @@ ValidVault::finalize(
                     result = false;
                 }
 
-                auto const assetTotalDelta =
-                    afterVault.assetsTotal - beforeVault.assetsTotal;
-                if (!withinDistance(assetTotalDelta, vaultDeltaAssets))
+                auto const assetTotalDelta = roundToAsset(
+                    vaultAsset,
+                    afterVault.assetsTotal - beforeVault.assetsTotal,
+                    minScale);
+                if (assetTotalDelta != vaultDeltaAssets)
                 {
                     JLOG(j.fatal()) << "Invariant failed: deposit and assets "
                                        "outstanding must add up";
                     result = false;
                 }
 
-                auto const assetAvailableDelta =
-                    afterVault.assetsAvailable - beforeVault.assetsAvailable;
-                if (!withinDistance(assetAvailableDelta, vaultDeltaAssets))
+                auto const assetAvailableDelta = roundToAsset(
+                    vaultAsset,
+                    afterVault.assetsAvailable - beforeVault.assetsAvailable,
+                    minScale);
+                if (assetAvailableDelta != vaultDeltaAssets)
                 {
                     JLOG(j.fatal()) << "Invariant failed: deposit and assets "
                                        "available must add up";
@@ -3355,7 +3426,24 @@ ValidVault::finalize(
                     return false;  // That's all we can do
                 }
 
-                auto const vaultPseudoDeltaAssets = *maybeVaultDeltaAssets;
+                // Get the most coarse scale to round calculations to
+                auto const totalDelta = DeltaInfo{
+                    afterVault.assetsTotal - beforeVault.assetsTotal,
+                    std::max(
+                        afterVault.assetsTotal.scale<STAmount>(vaultAsset),
+                        beforeVault.assetsTotal.scale<STAmount>(vaultAsset))};
+                auto const availableDelta = DeltaInfo{
+                    afterVault.assetsAvailable - beforeVault.assetsAvailable,
+                    std::max(
+                        afterVault.assetsAvailable.scale<STAmount>(vaultAsset),
+                        beforeVault.assetsAvailable.scale<STAmount>(
+                            vaultAsset))};
+                auto const minScale = computeMinScale(
+                    vaultAsset,
+                    {*maybeVaultDeltaAssets, totalDelta, availableDelta});
+
+                auto const vaultPseudoDeltaAssets = roundToAsset(
+                    vaultAsset, maybeVaultDeltaAssets->delta, minScale);
 
                 if (vaultPseudoDeltaAssets >= zero)
                 {
@@ -3377,7 +3465,7 @@ ValidVault::finalize(
                 {
                     auto const maybeAccDelta = deltaAssetsTxAccount();
                     auto const maybeOtherAccDelta =
-                        [&]() -> std::optional<Number> {
+                        [&]() -> std::optional<DeltaInfo> {
                         if (auto const destination = tx[~sfDestination];
                             destination && *destination != tx[sfAccount])
                             return deltaAssets(*destination);
@@ -3396,7 +3484,16 @@ ValidVault::finalize(
                     auto const destinationDelta =  //
                         maybeAccDelta ? *maybeAccDelta : *maybeOtherAccDelta;
 
-                    if (destinationDelta <= zero)
+                    // the scale of destinationDelta can be coarser than
+                    // minScale, so we take that into account when rounding
+                    auto const localMinScale = std::max(
+                        minScale,
+                        computeMinScale(vaultAsset, {destinationDelta}));
+
+                    auto const roundedDestinationDelta = roundToAsset(
+                        vaultAsset, destinationDelta.delta, localMinScale);
+
+                    if (roundedDestinationDelta <= zero)
                     {
                         JLOG(j.fatal()) <<  //
                             "Invariant failed: withdrawal must increase "
@@ -3404,8 +3501,9 @@ ValidVault::finalize(
                         result = false;
                     }
 
-                    if (!withinDistance(
-                            vaultPseudoDeltaAssets * -1, destinationDelta))
+                    auto const localPseudoDeltaAssets = roundToAsset(
+                        vaultAsset, vaultPseudoDeltaAssets, localMinScale);
+                    if (localPseudoDeltaAssets * -1 != roundedDestinationDelta)
                     {
                         JLOG(j.fatal()) <<  //
                             "Invariant failed: withdrawal must change vault "
@@ -3423,7 +3521,7 @@ ValidVault::finalize(
                     return false;
                 }
 
-                if (*accountDeltaShares >= zero)
+                if (accountDeltaShares->delta >= zero)
                 {
                     JLOG(j.fatal()) <<  //
                         "Invariant failed: withdrawal must decrease depositor "
@@ -3432,14 +3530,14 @@ ValidVault::finalize(
                 }
                 // We don't need to round shares, they are integral MPT
                 auto const vaultDeltaShares = deltaShares(afterVault.pseudoId);
-                if (!vaultDeltaShares || *vaultDeltaShares == zero)
+                if (!vaultDeltaShares || vaultDeltaShares->delta == zero)
                 {
                     JLOG(j.fatal()) <<  //
                         "Invariant failed: withdrawal must change vault shares";
                     return false;  // That's all we can do
                 }
 
-                if (*vaultDeltaShares * -1 != *accountDeltaShares)
+                if (vaultDeltaShares->delta * -1 != accountDeltaShares->delta)
                 {
                     JLOG(j.fatal()) <<  //
                         "Invariant failed: withdrawal must change depositor "
@@ -3447,20 +3545,24 @@ ValidVault::finalize(
                     result = false;
                 }
 
-                auto const assetTotalDelta =
-                    afterVault.assetsTotal - beforeVault.assetsTotal;
+                auto const assetTotalDelta = roundToAsset(
+                    vaultAsset,
+                    afterVault.assetsTotal - beforeVault.assetsTotal,
+                    minScale);
                 // Note, vaultBalance is negative (see check above)
-                if (!withinDistance(assetTotalDelta, vaultPseudoDeltaAssets))
+                if (assetTotalDelta != vaultPseudoDeltaAssets)
                 {
                     JLOG(j.fatal()) << "Invariant failed: withdrawal and "
                                        "assets outstanding must add up";
                     result = false;
                 }
 
-                auto const assetAvailableDelta =
-                    afterVault.assetsAvailable - beforeVault.assetsAvailable;
-                if (!withinDistance(
-                        assetAvailableDelta, vaultPseudoDeltaAssets))
+                auto const assetAvailableDelta = roundToAsset(
+                    vaultAsset,
+                    afterVault.assetsAvailable - beforeVault.assetsAvailable,
+                    minScale);
+
+                if (assetAvailableDelta != vaultPseudoDeltaAssets)
                 {
                     JLOG(j.fatal()) << "Invariant failed: withdrawal and "
                                        "assets available must add up";
@@ -3498,7 +3600,25 @@ ValidVault::finalize(
                     deltaAssets(afterVault.pseudoId);
                 if (maybeVaultDeltaAssets)
                 {
-                    auto const vaultDeltaAssets = *maybeVaultDeltaAssets;
+                    auto const totalDelta = DeltaInfo{
+                        afterVault.assetsTotal - beforeVault.assetsTotal,
+                        std::max(
+                            afterVault.assetsTotal.scale<STAmount>(vaultAsset),
+                            beforeVault.assetsTotal.scale<STAmount>(
+                                vaultAsset))};
+                    auto const availableDelta = DeltaInfo{
+                        afterVault.assetsAvailable -
+                            beforeVault.assetsAvailable,
+                        std::max(
+                            afterVault.assetsAvailable.scale<STAmount>(
+                                vaultAsset),
+                            beforeVault.assetsAvailable.scale<STAmount>(
+                                vaultAsset))};
+                    auto const minScale = computeMinScale(
+                        vaultAsset,
+                        {*maybeVaultDeltaAssets, totalDelta, availableDelta});
+                    auto const vaultDeltaAssets = roundToAsset(
+                        vaultAsset, maybeVaultDeltaAssets->delta, minScale);
                     if (vaultDeltaAssets >= zero)
                     {
                         JLOG(j.fatal()) <<  //
@@ -3507,22 +3627,24 @@ ValidVault::finalize(
                         result = false;
                     }
 
-                    auto const assetsTotalDelta =
-                        afterVault.assetsTotal - beforeVault.assetsTotal;
+                    auto const assetsTotalDelta = roundToAsset(
+                        vaultAsset,
+                        afterVault.assetsTotal - beforeVault.assetsTotal,
+                        minScale);
                     if (assetsTotalDelta != vaultDeltaAssets)
-                        if (!withinDistance(assetsTotalDelta, vaultDeltaAssets))
-                        {
-                            JLOG(j.fatal()) <<  //
-                                "Invariant failed: clawback and assets "
-                                "outstanding "
-                                "must add up";
-                            result = false;
-                        }
+                    {
+                        JLOG(j.fatal()) <<  //
+                            "Invariant failed: clawback and assets outstanding "
+                            "must add up";
+                        result = false;
+                    }
 
-                    auto const assetAvailableDelta =
+                    auto const assetAvailableDelta = roundToAsset(
+                        vaultAsset,
                         afterVault.assetsAvailable -
-                        beforeVault.assetsAvailable;
-                    if (!withinDistance(assetAvailableDelta, vaultDeltaAssets))
+                            beforeVault.assetsAvailable,
+                        minScale);
+                    if (assetAvailableDelta != vaultDeltaAssets)
                     {
                         JLOG(j.fatal()) <<  //
                             "Invariant failed: clawback and assets available "
@@ -3545,7 +3667,7 @@ ValidVault::finalize(
                         "Invariant failed: clawback must change holder shares";
                     return false;  // That's all we can do
                 }
-                if (*maybeAccountDeltaShares >= zero)
+                if (maybeAccountDeltaShares->delta >= zero)
                 {
                     JLOG(j.fatal()) <<  //
                         "Invariant failed: clawback must decrease holder "
@@ -3555,14 +3677,15 @@ ValidVault::finalize(
 
                 // We don't need to round shares, they are integral MPT
                 auto const vaultDeltaShares = deltaShares(afterVault.pseudoId);
-                if (!vaultDeltaShares || *vaultDeltaShares == zero)
+                if (!vaultDeltaShares || vaultDeltaShares->delta == zero)
                 {
                     JLOG(j.fatal()) <<  //
                         "Invariant failed: clawback must change vault shares";
                     return false;  // That's all we can do
                 }
 
-                if (*vaultDeltaShares * -1 != *maybeAccountDeltaShares)
+                if (vaultDeltaShares->delta * -1 !=
+                    maybeAccountDeltaShares->delta)
                 {
                     JLOG(j.fatal()) <<  //
                         "Invariant failed: clawback must change holder and "
@@ -3599,4 +3722,24 @@ ValidVault::finalize(
 
     return true;
 }
+
+[[nodiscard]] std::int32_t
+ValidVault::computeMinScale(
+    Asset const& asset,
+    std::vector<DeltaInfo> const& numbers)
+{
+    if (numbers.size() == 0)
+        return 0;
+
+    auto const max = std::max_element(
+        numbers.begin(),
+        numbers.end(),
+        [](auto const& a, auto const& b) -> bool { return a.scale < b.scale; });
+    XRPL_ASSERT_PARTS(
+        max->scale,
+        "xrpl::ValidVault::computeMinScale",
+        "scale set for destinationDelta");
+    return max->scale.value_or(STAmount::cMaxOffset);
+}
+
 }  // namespace xrpl

src/xrpld/app/tx/detail/InvariantCheck.h

@@ -879,11 +879,19 @@ class ValidVault
         Shares static make(SLE const&);
     };
 
+public:
+    struct DeltaInfo final
+    {
+        Number delta = numZero;
+        std::optional<int> scale;
+    };
+
+private:
     std::vector<Vault> afterVault_ = {};
     std::vector<Shares> afterMPTs_ = {};
     std::vector<Vault> beforeVault_ = {};
     std::vector<Shares> beforeMPTs_ = {};
-    std::unordered_map<uint256, Number> deltas_ = {};
+    std::unordered_map<uint256, DeltaInfo> deltas_ = {};
 
 public:
     void
@@ -899,6 +907,10 @@ public:
         XRPAmount const,
         ReadView const&,
         beast::Journal const&);
+
+    // Compute the coarsest scale required to represent all numbers
+    [[nodiscard]] static std::int32_t
+    computeMinScale(Asset const& asset, std::vector<DeltaInfo> const& numbers);
 };
 
 // additional invariant checks can be declared above and then added to this

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

@@ -125,7 +125,7 @@ LoanBrokerCoverWithdraw::preclaim(PreclaimContext const& ctx)
             tenthBipsOfValue(
                 currentDebtTotal,
                 TenthBips32(sleBroker->at(sfCoverRateMinimum))),
-            currentDebtTotal.exponent());
+            currentDebtTotal.scale<STAmount>(vaultAsset));
     }();
     if (coverAvail < amount)
         return tecINSUFFICIENT_FUNDS;