Include rounding mode in XRPAmount to STAmount conversion.

src/ripple/basics/IOUAmount.h

@@ -186,10 +186,6 @@ mulRatio(
     std::uint32_t den,
     bool roundUp);
 
-// Since IOUAmount and STAmount do not have access to a ledger, this
-// is needed to put low-level routines on an amendment switch. Only
-// transactions need to use this switchover. Outside of a transaction
-// it's safe to unconditionally use the new behavior.
 extern LocalValue<bool> stNumberSwitchover;
 
 /** RAII class to set and restore the Number switchover.

src/ripple/basics/Number.h

@@ -337,6 +337,24 @@ squelch(Number const& x, Number const& limit) noexcept
     return x;
 }
 
+class saveNumberRoundMode
+{
+    Number::rounding_mode mode_;
+
+public:
+    ~saveNumberRoundMode()
+    {
+        Number::setround(mode_);
+    }
+    explicit saveNumberRoundMode(Number::rounding_mode mode) noexcept
+        : mode_{mode}
+    {
+    }
+    saveNumberRoundMode(saveNumberRoundMode const&) = delete;
+    saveNumberRoundMode&
+    operator=(saveNumberRoundMode const&) = delete;
+};
+
 }  // namespace ripple
 
 #endif  // RIPPLE_BASICS_NUMBER_H_INCLUDED