Use CHAR_BIT instead of assuming 8 bits

	* src/c++11/random.cc (random_device::_M_getentropy): Use __CHAR_BIT__
	instead of fixed number of bits.

From-SVN: r248428

libstdc++-v3/ChangeLog

+2017-05-24  Jonathan Wakely  <jwakely@redhat.com>
+
+	* src/c++11/random.cc (random_device::_M_getentropy): Use __CHAR_BIT__
+	instead of fixed number of bits.
+
 2017-05-24  Andreas Schwab  <schwab@suse.de>
 
 	* config/abi/post/ia64-linux-gnu/baseline_symbols.txt: Update.

libstdc++-v3/src/c++11/random.cc

@@ -187,8 +187,9 @@ namespace std _GLIBCXX_VISIBILITY(default)
     if (ent < 0)
       return 0.0;
 
-    if (static_cast<unsigned>(ent) > sizeof(result_type) * 8)
-      return static_cast<double>(sizeof(result_type) * 8);
+    const int max = sizeof(result_type) * __CHAR_BIT__;
+    if (ent > max)
+      ent = max;
 
     return static_cast<double>(ent);
 #else