cql3: castas_fcts: workaround boost bug casting multiprecision intege…

…rs to floats

In [1] a bug casting large multiprecision integers to floats is documented. Until
the fix propagates, work around it by detecting the conditions that trigger the bug
and returning the expected result.

Fixes scylladb#18508

[1] boostorg/multiprecision#553

cql3/functions/castas_fcts.cc

@@ -69,6 +69,16 @@ using bytes_opt = std::optional<bytes>;
 template<typename ToType, typename FromType>
 static data_value castas_fctn_simple(data_value from) {
     auto val_from = value_cast<FromType>(from);
+    // Workaround for https://github.com/boostorg/multiprecision/issues/553 (the additional bug discovered post-closing)
+    if constexpr (std::is_floating_point_v<ToType> && std::is_same_v<FromType, utils::multiprecision_int>) {
+        static auto min = utils::multiprecision_int(std::numeric_limits<ToType>::lowest());
+        static auto max = utils::multiprecision_int(std::numeric_limits<ToType>::max());
+        if (val_from < min) {
+            return -std::numeric_limits<ToType>::infinity();
+        } else if (val_from > max) {
+            return std::numeric_limits<ToType>::infinity();
+        }
+    }
     return static_cast<ToType>(val_from);
 }