hashtable.h (clear): Return quickly if the table is empty.

	* include/backward/hashtable.h (clear): Return quickly if the
	table is empty.

From-SVN: r145318

libstdc++-v3/ChangeLog

+2009-03-30  Ian Lance Taylor  <iant@google.com>
+
+	* include/backward/hashtable.h (clear): Return quickly if the
+	table is empty.
+
 2009-03-27  Ian Lance Taylor  <iant@google.com>
 
 	* include/backward/hashtable.h (_S_num_primes): Change to 29.

libstdc++-v3/include/backward/hashtable.h

@@ -1076,6 +1076,9 @@ _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)
     hashtable<_Val, _Key, _HF, _Ex, _Eq, _All>::
     clear()
     {
+      if (_M_num_elements == 0)
+	return;
+
       for (size_type __i = 0; __i < _M_buckets.size(); ++__i)
 	{
 	  _Node* __cur = _M_buckets[__i];