alpaka::AtomicCas add floating point support

include/alpaka/atomic/Op.hpp

@@ -13,6 +13,9 @@
 #include <alpaka/core/Common.hpp>
 
 #include <algorithm>
+#include <type_traits>
+#include <variant>
+
 
 namespace alpaka
 {
@@ -112,7 +115,7 @@ namespace alpaka
         {
             auto const old = *addr;
             auto& ref = *addr;
-            ref = ((old >= value) ? 0 : static_cast<T>(old + 1));
+            ref = ((old >= value) ? static_cast<T>(0) : static_cast<T>(old + static_cast<T>(1)));
             return old;
         }
     };
@@ -128,7 +131,7 @@ namespace alpaka
         {
             auto const old = *addr;
             auto& ref = *addr;
-            ref = (((old == 0) || (old > value)) ? value : static_cast<T>(old - 1));
+            ref = (((old == static_cast<T>(0)) || (old > value)) ? value : static_cast<T>(old - static_cast<T>(1)));
             return old;
         }
     };
@@ -177,9 +180,14 @@ namespace alpaka
     //! The compare and swap function object.
     struct AtomicCas
     {
-        //! \return The old value of addr.
-        ALPAKA_NO_HOST_ACC_WARNING
+        // allow reinterpreting any type up to 64bit in size for bitwise interpretation.
         template<typename T>
+        using reinterpret = std::variant<T, std::conditional_t<sizeof(T) == 4u, unsigned int, unsigned long long>>;
+
+        //! AtomicCas for non floating point values
+        // \return The old value of addr.
+        ALPAKA_NO_HOST_ACC_WARNING
+        template<typename T, std::enable_if_t<!std::is_floating_point_v<T>, bool> = true>
         ALPAKA_FN_HOST_ACC auto operator()(T* addr, T const& compare, T const& value) const -> T
         {
             auto const old = *addr;
@@ -191,9 +199,36 @@ namespace alpaka
 #    pragma GCC diagnostic push
 #    pragma GCC diagnostic ignored "-Wstrict-overflow"
 #endif
+            // check if values are bit-wise equal
             ref = ((old == compare) ? value : old);
 #if BOOST_COMP_GNUC && (BOOST_COMP_GNUC == BOOST_VERSION_NUMBER(7, 4, 0))
 #    pragma GCC diagnostic pop
+#endif
+            return old;
+        }
+        //! AtomicCas for floating point values
+        // \return The old value of addr.
+        ALPAKA_NO_HOST_ACC_WARNING
+        template<typename T, std::enable_if_t<std::is_floating_point_v<T>, bool> = true>
+        ALPAKA_FN_HOST_ACC auto operator()(T* addr, T const& compare, T const& value) const -> T
+        {
+            static_assert(sizeof(T) == 4u || sizeof(T) == 8u, "AtomicCas is supporting only 32bit and 64bit values!");
+
+            auto const old = *addr;
+            auto& ref = *addr;
+
+// gcc-7.4.0 assumes for an optimization that a signed overflow does not occur here.
+// That's fine, so ignore that warning.
+#if BOOST_COMP_GNUC && (BOOST_COMP_GNUC == BOOST_VERSION_NUMBER(7, 4, 0))
+#    pragma GCC diagnostic push
+#    pragma GCC diagnostic ignored "-Wstrict-overflow"
+#endif
+            // check if values are bit-wise equal
+            auto const o = std::get<1>(reinterpret<T>(std::in_place_index<1>, old));
+            auto const c = std::get<1>(reinterpret<T>(std::in_place_index<1>, compare));
+            ref = ((o == c) ? value : old);
+#if BOOST_COMP_GNUC && (BOOST_COMP_GNUC == BOOST_VERSION_NUMBER(7, 4, 0))
+#    pragma GCC diagnostic pop
 #endif
             return old;
         }