refactor

include/xrpl/basics/Number.h

@@ -392,6 +392,20 @@ public:
     static RoundingMode
     setround(RoundingMode inMode);
 
+    /** Convert an integer to a RoundingMode, validating that it is in range.
+     *
+     * Returns std::nullopt if the value does not correspond to a valid
+     * RoundingMode.
+     */
+    static std::optional<RoundingMode>
+    checkedRoundingMode(int mode) noexcept
+    {
+        if (mode < static_cast<int>(RoundingMode::ToNearest) ||
+            mode > static_cast<int>(RoundingMode::Upward))
+            return std::nullopt;
+        return static_cast<RoundingMode>(mode);
+    }
+
     /** Returns which mantissa scale is currently in use for normalization.
      *
      * If you think you need to call this outside of unit tests, no you don't.

src/libxrpl/tx/wasm/HostFuncImplFloat.cpp

@@ -81,26 +81,20 @@ floatEncode(Number const& n)
 
 struct FloatState
 {
-    Number::RoundingMode oldMode;
-    bool good = false;
+    // Set only when the requested mode is valid; sets the rounding mode on
+    // construction and restores the previous mode on destruction.
+    std::optional<NumberRoundModeGuard> guard_;
 
-    FloatState(int32_t mode) : oldMode(Number::getround())
+    explicit FloatState(int32_t mode)
     {
-        if (mode < static_cast<int32_t>(Number::RoundingMode::ToNearest) ||
-            mode > static_cast<int32_t>(Number::RoundingMode::Upward))
-            return;
-        Number::setround(static_cast<Number::RoundingMode>(mode));
-        good = true;
-    }
-
-    ~FloatState()
-    {
-        Number::setround(oldMode);
+        if (auto const rm = Number::checkedRoundingMode(mode))
+            guard_.emplace(*rm);
     }
 
+    explicit
     operator bool() const
     {
-        return good;
+        return guard_.has_value();
     }
 };