Implement batch_bool::mask() for riscv

As a followup to #1236

Author: serge-sans-paille

include/xsimd/arch/xsimd_rvv.hpp

@@ -1507,6 +1507,16 @@ namespace xsimd
             const auto mask = abs(arg) < constants::maxflint<batch<T, A>>();
             return select(mask, to_float(detail::rvvfcvt_default(arg)), arg, rvv {});
         }
+
+        // mask
+        template <class A, class T>
+        XSIMD_INLINE uint64_t mask(batch_bool<T, A> const& self, requires_arch<rvv>) noexcept
+        {
+            auto ones = detail::broadcast<as_unsigned_integer_t<T>, A::width>(1);
+            auto iota = detail::vindex<A, T>();
+            auto powers = detail::rvvsll(ones, iota);
+            return __riscv_vredor(self.data, powers);
+        }
     } // namespace kernel
 } // namespace xsimd