From 8cfea5a9d1aafdc80f8461cabdc86ed46bb16463 Mon Sep 17 00:00:00 2001
From: Scott Determan <scott.determan@yahoo.com>
Date: Fri, 22 Mar 2024 17:02:17 -0400
Subject: [PATCH] fixXChainRewardRounding: round reward shares down: (#4933)

When calculating reward shares, the amount should always be rounded
down. If the `fixUniversalNumber` amendment is not active, this works
correctly. If it is not active, then the amount is incorrectly rounded
up. This patch introduces an amendment so it will be rounded down.
---
 src/ripple/app/tx/impl/XChainBridge.cpp | 8 +++++++-
 src/ripple/protocol/Feature.h           | 3 ++-
 src/ripple/protocol/impl/Feature.cpp    | 1 +
 3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/ripple/app/tx/impl/XChainBridge.cpp b/src/ripple/app/tx/impl/XChainBridge.cpp
index 934a88f55..c952aef23 100644
--- a/src/ripple/app/tx/impl/XChainBridge.cpp
+++ b/src/ripple/app/tx/impl/XChainBridge.cpp
@@ -22,6 +22,7 @@
 #include <ripple/app/tx/impl/Transactor.h>
 #include <ripple/app/tx/impl/XChainBridge.h>
 #include <ripple/basics/Log.h>
+#include <ripple/basics/Number.h>
 #include <ripple/basics/XRPAmount.h>
 #include <ripple/basics/chrono.h>
 #include <ripple/beast/utility/Journal.h>
@@ -41,7 +42,6 @@
 #include <ripple/protocol/XChainAttestations.h>
 #include <ripple/protocol/digest.h>
 #include <ripple/protocol/st.h>
-
 #include <unordered_map>
 #include <unordered_set>
 
@@ -675,6 +675,12 @@ finalizeClaimHelper(
             // if the transfer failed, distribute the pool for "OnTransferFail"
             // cases (the attesters did their job)
             STAmount const share = [&] {
+                auto const round_mode =
+                    innerSb.rules().enabled(fixXChainRewardRounding)
+                    ? Number::rounding_mode::downward
+                    : Number::getround();
+                saveNumberRoundMode _{Number::setround(round_mode)};
+
                 STAmount const den{rewardAccounts.size()};
                 return divide(rewardPool, den, rewardPool.issue());
             }();
diff --git a/src/ripple/protocol/Feature.h b/src/ripple/protocol/Feature.h
index 87c4806ab..e29db1ac7 100644
--- a/src/ripple/protocol/Feature.h
+++ b/src/ripple/protocol/Feature.h
@@ -74,7 +74,7 @@ namespace detail {
 // Feature.cpp. Because it's only used to reserve storage, and determine how
 // large to make the FeatureBitset, it MAY be larger. It MUST NOT be less than
 // the actual number of amendments. A LogicError on startup will verify this.
-static constexpr std::size_t numFeatures = 93;
+static constexpr std::size_t numFeatures = 94;
 
 /** Amendments that this server supports and the default voting behavior.
    Whether they are enabled depends on the Rules defined in the validated
@@ -381,6 +381,7 @@ extern uint256 const fixInnerObjTemplate;
 extern uint256 const fixAMMOverflowOffer;
 extern uint256 const featurePriceOracle;
 extern uint256 const fixEmptyDID;
+extern uint256 const fixXChainRewardRounding;
 
 }  // namespace ripple
 
diff --git a/src/ripple/protocol/impl/Feature.cpp b/src/ripple/protocol/impl/Feature.cpp
index f6174c23c..7b239e13b 100644
--- a/src/ripple/protocol/impl/Feature.cpp
+++ b/src/ripple/protocol/impl/Feature.cpp
@@ -487,6 +487,7 @@ REGISTER_FIX    (fixInnerObjTemplate,           Supported::yes, VoteBehavior::De
 REGISTER_FIX    (fixAMMOverflowOffer,           Supported::yes, VoteBehavior::DefaultYes);
 REGISTER_FEATURE(PriceOracle,                   Supported::yes, VoteBehavior::DefaultNo);
 REGISTER_FIX    (fixEmptyDID,                   Supported::yes, VoteBehavior::DefaultNo);
+REGISTER_FIX    (fixXChainRewardRounding,       Supported::yes, VoteBehavior::DefaultNo);
 
 // The following amendments are obsolete, but must remain supported
 // because they could potentially get enabled.