[PATCH 4/5] barrier: use int instead of unsigned char for the phase state

[Thiago Macieira via Gcc-patches]

ints can be used in futexes. chars can't.
---
 libstdc++-v3/include/std/barrier | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/libstdc++-v3/include/std/barrier b/libstdc++-v3/include/std/barrier
index e09212dfcb9..ae058bd3dc3 100644
--- a/libstdc++-v3/include/std/barrier
+++ b/libstdc++-v3/include/std/barrier
@@ -70,7 +70,7 @@ It looks different from literature pseudocode for two main 
reasons:
 
 */
 
-  enum class __barrier_phase_t : unsigned char { };
+  enum class __barrier_phase_t : int { };
 
   template<typename _CompletionF>
     class __tree_barrier
@@ -93,20 +93,24 @@ It looks different from literature pseudocode for two main 
reasons:
 
       alignas(__phase_alignment) __barrier_phase_t  _M_phase;
 
+      static __barrier_phase_t
+      _S_add_to_phase(__barrier_phase_t __phase, unsigned char __n)
+      {
+        __n += static_cast<unsigned char>(__phase);
+        return static_cast<__barrier_phase_t>(__n);
+      }
+
       bool
       _M_arrive(__barrier_phase_t __old_phase)
       {
-       const auto __old_phase_val = static_cast<unsigned char>(__old_phase);
-       const auto __half_step =
-                          static_cast<__barrier_phase_t>(__old_phase_val + 1);
-       const auto __full_step =
-                          static_cast<__barrier_phase_t>(__old_phase_val + 2);
-
        size_t __current_expected = _M_expected;
        std::hash<std::thread::id> __hasher;
        size_t __current = __hasher(std::this_thread::get_id())
                                          % ((_M_expected + 1) >> 1);
 
+       const auto __half_step = _S_add_to_phase(__old_phase, 1);
+       const auto __full_step = _S_add_to_phase(__old_phase, 2);
+
        for (int __round = 0; ; ++__round)
          {
            if (__current_expected <= 1)
@@ -165,7 +169,6 @@ It looks different from literature pseudocode for two main 
reasons:
       {
        __atomic_phase_ref_t __phase(_M_phase);
        const auto __old_phase = __phase.load(memory_order_relaxed);
-       const auto __cur = static_cast<unsigned char>(__old_phase);
        for(; __update; --__update)
          {
            if(_M_arrive(__old_phase))
@@ -173,7 +176,7 @@ It looks different from literature pseudocode for two main 
reasons:
                _M_completion();
                _M_expected += 
_M_expected_adjustment.load(memory_order_relaxed);
                _M_expected_adjustment.store(0, memory_order_relaxed);
-               auto __new_phase = static_cast<__barrier_phase_t>(__cur + 2);
+               auto __new_phase = _S_add_to_phase(__old_phase, 2);
                __phase.store(__new_phase, memory_order_release);
                __phase.notify_all();
              }
-- 
2.30.1