From 58b22901cb12e8442fe7023a6a6c7bd866456f34 Mon Sep 17 00:00:00 2001
From: Denis Angell <dangell@transia.co>
Date: Sat, 9 Nov 2024 06:17:00 +0100
Subject: [PATCH] Fix: `float_divide` rounding error (#351)

Co-authored-by: RichardAH <richard.holland@starstone.co.nz>
---
 src/ripple/app/hook/impl/applyHook.cpp | 21 ++++++++++++++++-----
 src/ripple/protocol/Feature.h          |  3 ++-
 src/ripple/protocol/impl/Feature.cpp   |  1 +
 3 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/src/ripple/app/hook/impl/applyHook.cpp b/src/ripple/app/hook/impl/applyHook.cpp
index 2afd018e8..abd7ef136 100644
--- a/src/ripple/app/hook/impl/applyHook.cpp
+++ b/src/ripple/app/hook/impl/applyHook.cpp
@@ -5404,7 +5404,7 @@ DEFINE_HOOK_FUNCTION(
 const int64_t float_one_internal = make_float(1000000000000000ull, -15, false);
 
 inline int64_t
-float_divide_internal(int64_t float1, int64_t float2)
+float_divide_internal(int64_t float1, int64_t float2, bool hasFix)
 {
     RETURN_IF_INVALID_FLOAT(float1);
     RETURN_IF_INVALID_FLOAT(float2);
@@ -5457,8 +5457,16 @@ float_divide_internal(int64_t float1, int64_t float2)
     while (man2 > 0)
     {
         int i = 0;
-        for (; man1 > man2; man1 -= man2, ++i)
-            ;
+        if (hasFix)
+        {
+            for (; man1 >= man2; man1 -= man2, ++i)
+                ;
+        }
+        else
+        {
+            for (; man1 > man2; man1 -= man2, ++i)
+                ;
+        }
 
         man3 *= 10;
         man3 += i;
@@ -5478,7 +5486,8 @@ DEFINE_HOOK_FUNCTION(int64_t, float_divide, int64_t float1, int64_t float2)
     HOOK_SETUP();  // populates memory_ctx, memory, memory_length, applyCtx,
                    // hookCtx on current stack
 
-    return float_divide_internal(float1, float2);
+    bool const hasFix = view.rules().enabled(fixFloatDivide);
+    return float_divide_internal(float1, float2, hasFix);
 
     HOOK_TEARDOWN();
 }
@@ -5497,7 +5506,9 @@ DEFINE_HOOK_FUNCTION(int64_t, float_invert, int64_t float1)
         return DIVISION_BY_ZERO;
     if (float1 == float_one_internal)
         return float_one_internal;
-    return float_divide_internal(float_one_internal, float1);
+
+    bool const fixV3 = view.rules().enabled(fixFloatDivide);
+    return float_divide_internal(float_one_internal, float1, fixV3);
 
     HOOK_TEARDOWN();
 }
diff --git a/src/ripple/protocol/Feature.h b/src/ripple/protocol/Feature.h
index 54628c9cd..43d510c63 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 = 73;
+static constexpr std::size_t numFeatures = 74;
 
 /** Amendments that this server supports and the default voting behavior.
    Whether they are enabled depends on the Rules defined in the validated
@@ -361,6 +361,7 @@ extern uint256 const fixNSDelete;
 extern uint256 const fix240819;
 extern uint256 const fixPageCap;
 extern uint256 const fix240911;
+extern uint256 const fixFloatDivide;
 
 }  // namespace ripple
 
diff --git a/src/ripple/protocol/impl/Feature.cpp b/src/ripple/protocol/impl/Feature.cpp
index 27ec16cb7..23cbe236d 100644
--- a/src/ripple/protocol/impl/Feature.cpp
+++ b/src/ripple/protocol/impl/Feature.cpp
@@ -467,6 +467,7 @@ REGISTER_FIX    (fixNSDelete,                   Supported::yes, VoteBehavior::De
 REGISTER_FIX    (fix240819,                     Supported::yes, VoteBehavior::DefaultYes);
 REGISTER_FIX    (fixPageCap,                    Supported::yes, VoteBehavior::DefaultYes);
 REGISTER_FIX    (fix240911,                     Supported::yes, VoteBehavior::DefaultYes);
+REGISTER_FIX    (fixFloatDivide,                Supported::yes, VoteBehavior::DefaultYes);
 
 // The following amendments are obsolete, but must remain supported
 // because they could potentially get enabled.