kokkos#120: atomic_compare_exchange md to rst

docs/source/API/core/atomics/atomic_compare_exchange.rst

@@ -0,0 +1,41 @@
+``atomic_compare_exchange``
+===========================
+
+.. role::cpp(code)
+    :language: cpp
+
+Header File: ``Kokkos_Core.hpp``
+
+Usage:
+
+.. code-block:: cpp
+
+    old_val = atomic_compare_exchange(ptr_to_value,comparison_value, new_value);
+
+
+Atomically sets the value at the address given by ``ptr_to_value`` to ``new_value`` if the current value at ``ptr_to_value``
+is equal to ``comparison_value``, and returns the previously stored value at the address independent on whether 
+the exchange has happened.
+
+Synopsis
+--------
+
+.. code-block:: cpp
+
+    template<class T>
+    T atomic_compare_exchange(T* const ptr_to_value, const T comparison_value, const T new_value);
+
+Description
+-----------
+
+- .. code-block:: cpp
+
+    template<class T>
+    T atomic_compare_exchange(T* const ptr_to_value, const T comparison_value, const T new_value);
+
+  Atomically executes ``old_value = *ptr_to_value; if(old_value==comparison_value) *ptr_to_value = new_value; return old_value;``.
+
+  - ``ptr_to_value``: address of the to be updated value.
+  - ``comparison_value``: value to be compared to. 
+  - ``new_value``: new value.
+  - ``old_value``: value at address ``ptr_to_value`` before doing the exchange.