Use Number for IOUAmount and STAmount arithmetic

* Guarded by amendment fixUniversalNumber
* Produces slightly better accuracy in some computations.

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 = 55;
+static constexpr std::size_t numFeatures = 56;
 
 /** Amendments that this server supports and the default voting behavior.
    Whether they are enabled depends on the Rules defined in the validated
@@ -340,8 +340,12 @@ extern uint256 const featureNonFungibleTokensV1_1;
 extern uint256 const fixTrustLinesToSelf;
 extern uint256 const fixRemoveNFTokenAutoTrustLine;
 extern uint256 const featureImmediateOfferKilled;
+<<<<<<< HEAD
 extern uint256 const featureDisallowIncoming;
 extern uint256 const featureXRPFees;
+=======
+extern uint256 const fixUniversalNumber;
+>>>>>>> Use Number for IOUAmount and STAmount arithmetic
 
 }  // namespace ripple
 

src/ripple/protocol/STAmount.h

@@ -277,7 +277,13 @@ private:
     STBase*
     move(std::size_t n, void* buf) override;
 
+    STAmount&
+    operator=(IOUAmount const& iou);
+
     friend class detail::STVar;
+
+    friend STAmount
+    operator+(STAmount const& v1, STAmount const& v2);
 };
 
 //------------------------------------------------------------------------------

src/ripple/protocol/impl/Feature.cpp

@@ -452,6 +452,7 @@ REGISTER_FIX    (fixRemoveNFTokenAutoTrustLine, Supported::yes, DefaultVote::yes
 REGISTER_FEATURE(ImmediateOfferKilled,          Supported::yes, DefaultVote::no);
 REGISTER_FEATURE(DisallowIncoming,              Supported::yes, DefaultVote::no);
 REGISTER_FEATURE(XRPFees,                       Supported::yes, DefaultVote::no);
+REGISTER_FIX    (fixUniversalNumber,            Supported::yes, DefaultVote::yes);
 
 // The following amendments have been active for at least two years. Their
 // pre-amendment code has been removed and the identifiers are deprecated.

src/ripple/protocol/impl/STAmount.cpp

@@ -339,6 +339,19 @@ STAmount::iou() const
     return {mantissa, exponent};
 }
 
+STAmount&
+STAmount::operator=(IOUAmount const& iou)
+{
+    assert(mIsNative == false);
+    mOffset = iou.exponent();
+    mIsNegative = iou < beast::zero;
+    if (mIsNegative)
+        mValue = static_cast<std::uint64_t>(-iou.mantissa());
+    else
+        mValue = static_cast<std::uint64_t>(iou.mantissa());
+    return *this;
+}
+
 //------------------------------------------------------------------------------
 //
 // Operators
@@ -382,6 +395,13 @@ operator+(STAmount const& v1, STAmount const& v2)
     if (v1.native())
         return {v1.getFName(), getSNValue(v1) + getSNValue(v2)};
 
+    if (*stNumberSwitchover)
+    {
+        auto x = v1;
+        x = v1.iou() + v2.iou();
+        return x;
+    }
+
     int ov1 = v1.exponent(), ov2 = v2.exponent();
     std::int64_t vv1 = static_cast<std::int64_t>(v1.mantissa());
     std::int64_t vv2 = static_cast<std::int64_t>(v2.mantissa());
@@ -733,6 +753,12 @@ STAmount::canonicalize()
 
     mIsNative = false;
 
+    if (*stNumberSwitchover)
+    {
+        *this = iou();
+        return;
+    }
+
     if (mValue == 0)
     {
         mOffset = -100;
@@ -1170,6 +1196,9 @@ multiply(STAmount const& v1, STAmount const& v2, Issue const& issue)
         return STAmount(v1.getFName(), minV * maxV);
     }
 
+    if (*stNumberSwitchover)
+        return {IOUAmount{Number{v1} * Number{v2}}, issue};
+
     std::uint64_t value1 = v1.mantissa();
     std::uint64_t value2 = v2.mantissa();
     int offset1 = v1.exponent();