[PATCH] Implement std::advance for istreambuf_iterator using pubseekoff

[François Dumont <frs dot dumont at gmail dot com>]

The same way I proposed to review std::copy overload for 
istreambuf_iterator we can implement std::advance using pubseekoff.

It is both a cleaner implementation and avoids yet another friend 
declaration.


    * include/std/streambuf
    (advance(istreambuf_iterator<>&, _Distance)): Remove friend 
declaration.
    * include/bits/streambuf_iterator.h (__copy_move_a2): Re-implement 
using
    streambuf pubseekoff.

Tested under Linux x86_64.

Ok to commit ?

François

diff --git a/libstdc++-v3/include/bits/streambuf_iterator.h b/libstdc++-v3/include/bits/streambuf_iterator.h
index 134b3486b9a..afe5c95f021 100644
--- a/libstdc++-v3/include/bits/streambuf_iterator.h
+++ b/libstdc++-v3/include/bits/streambuf_iterator.h
@@ -434,34 +434,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 			      _M_message(__gnu_debug::__msg_inc_istreambuf)
 			      ._M_iterator(__i));
 
-      typedef istreambuf_iterator<_CharT>		   __is_iterator_type;
-      typedef typename __is_iterator_type::traits_type	   traits_type;
-      typedef typename __is_iterator_type::streambuf_type  streambuf_type;
-      typedef typename traits_type::int_type		   int_type;
-      const int_type __eof = traits_type::eof();
-
-      streambuf_type* __sb = __i._M_sbuf;
-      while (__n > 0)
-	{
-	  streamsize __size = __sb->egptr() - __sb->gptr();
-	  if (__size > __n)
-	    {
-	      __sb->__safe_gbump(__n);
-	      break;
-	    }
-
-	  __sb->__safe_gbump(__size);
-	  __n -= __size;
-	  if (traits_type::eq_int_type(__sb->underflow(), __eof))
-	    {
-	      __glibcxx_requires_cond(__n == 0,
-				_M_message(__gnu_debug::__msg_inc_istreambuf)
-				._M_iterator(__i));
-	      break;
-	    }
-	}
+#ifdef _GLIBCXX_DEBUG
+      typedef basic_streambuf<_CharT> __streambuf_t;
+      typedef typename __streambuf_t::pos_type __pos_type;
+      __pos_type __cur_pos
+	= __i._M_sbuf->pubseekoff(0, ios_base::cur, ios_base::in);
+      __pos_type __new_pos =
+#endif
+      __i._M_sbuf->pubseekoff(__n, ios_base::cur, ios_base::in);
+      __i._M_c = char_traits<_CharT>::eof();
 
-      __i._M_c = __eof;
+      __glibcxx_requires_cond(__new_pos - __cur_pos == __n,
+			      _M_message(__gnu_debug::__msg_inc_istreambuf)
+			      ._M_iterator(__i));
     }
 
 // @} group iterators
diff --git a/libstdc++-v3/include/std/streambuf b/libstdc++-v3/include/std/streambuf
index 3442f19bd78..ef03da39bc2 100644
--- a/libstdc++-v3/include/std/streambuf
+++ b/libstdc++-v3/include/std/streambuf
@@ -155,11 +155,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
         find(istreambuf_iterator<_CharT2>, istreambuf_iterator<_CharT2>,
 	     const _CharT2&);
 
-      template<typename _CharT2, typename _Distance>
-        friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value,
-					       void>::__type
-        advance(istreambuf_iterator<_CharT2>&, _Distance);
-
       template<typename _CharT2, typename _Traits2>
         friend basic_istream<_CharT2, _Traits2>&
         operator>>(basic_istream<_CharT2, _Traits2>&, _CharT2*);