Improve implementations of __set_difference_construct() and __set_symmetric_difference_construct()

include/oneapi/dpl/pstl/parallel_backend_utils.h

@@ -280,25 +280,36 @@ __set_difference_construct(_ForwardIterator1 __first1, _ForwardIterator1 __last1
 {
     using _Tp = typename ::std::iterator_traits<_OutputIterator>::value_type;
 
-    for (; __first1 != __last1;)
+    // __proj1_val < __proj2_val
+    auto __op_val1_lt_val2 = [](_ForwardIterator1& __it1, _ForwardIterator2&, _OutputIterator& __out_it) {
+        ::new (::std::addressof(*__out_it)) _Tp(*__it1);
+        ++__it1;
+        ++__out_it;
+    };
+
+    // __proj2_val < __proj1_val
+    auto __op_val2_lt_val1 = [](_ForwardIterator1&, _ForwardIterator2& __it2, _OutputIterator&) { ++__it2; };
+
+    // __proj1_val == __proj2_val
+    auto __op_val1_eq_val2 = [](_ForwardIterator1& __it1, _ForwardIterator2& __it2, _OutputIterator&) {
+        ++__it1;
+        ++__it2;
+    };
+
+    // 1. Main set_difference operation
+    while (__first1 != __last1 && __first2 != __last2)
     {
-        if (__first2 == __last2)
-            return __cc_range(__first1, __last1, __result);
-
-        if (std::invoke(__comp, std::invoke(__proj1, *__first1), std::invoke(__proj2, *__first2)))
-        {
-            ::new (::std::addressof(*__result)) _Tp(*__first1);
-            ++__result;
-            ++__first1;
-        }
-        else
-        {
-            if (!std::invoke(__comp, std::invoke(__proj2, *__first2), std::invoke(__proj1, *__first1)))
-                ++__first1;
-            ++__first2;
-        }
+        const bool __val1_lt_val2 =
+            std::invoke(__comp, std::invoke(__proj1, *__first1), std::invoke(__proj2, *__first2));
+        const bool __val2_lt_val1 =
+            !__val1_lt_val2 && std::invoke(__comp, std::invoke(__proj2, *__first2), std::invoke(__proj1, *__first1));
+
+        __val1_lt_val2 ? __op_val1_lt_val2(__first1, __first2, __result)
+                       : (__val2_lt_val1 ? __op_val2_lt_val1(__first1, __first2, __result)
+                                         : __op_val1_eq_val2(__first1, __first2, __result));
     }
-    return __result;
+
+    return __cc_range(__first1, __last1, __result);
 }
 
 template <typename _ForwardIterator1, typename _ForwardIterator2, typename _OutputIterator,
@@ -310,11 +321,8 @@ __set_symmetric_difference_construct(_ForwardIterator1 __first1, _ForwardIterato
 {
     using _Tp = typename ::std::iterator_traits<_OutputIterator>::value_type;
 
-    for (; __first1 != __last1;)
+    while (__first1 != __last1 && __first2 != __last2)
     {
-        if (__first2 == __last2)
-            return __cc_range(__first1, __last1, __result);
-
         if (std::invoke(__comp, std::invoke(__proj1, *__first1), std::invoke(__proj2, *__first2)))
         {
             ::new (::std::addressof(*__result)) _Tp(*__first1);
@@ -333,7 +341,11 @@ __set_symmetric_difference_construct(_ForwardIterator1 __first1, _ForwardIterato
             ++__first2;
         }
     }
-    return __cc_range(__first2, __last2, __result);
+
+    if (__first1 == __last1)
+        return __cc_range(__first2, __last2, __result);
+
+    return __cc_range(__first1, __last1, __result);
 }
 
 template <template <typename, typename...> typename _Concrete, typename _ValueType, typename... _Args>