Added an atomic max for chars

src/atomic.h

@@ -121,6 +121,27 @@ __attribute__((always_inline)) INLINE static void atomic_min_d(
   } while (test_val.as_long_long != old_val.as_long_long);
 }
 
+/**
+ * @brief Atomic max operation on chars.
+ *
+ * This is a text-book implementation based on an atomic CAS.
+ *
+ * @param address The address to update.
+ * @param y The value to update the address with.
+ */
+__attribute__((always_inline)) INLINE static void atomic_max_c(
+    volatile char *const address, const char y) {
+
+  char test_val, old_val, new_val;
+  old_val = *address;
+
+  do {
+    test_val = old_val;
+    new_val = max(old_val, y);
+    old_val = atomic_cas(address, test_val, new_val);
+  } while (test_val != old_val);
+}
+
 /**
  * @brief Atomic max operation on floats.
  *