Re: [libstdc++/71500] make back reference work with icase

[Jonathan Wakely <jwakely at redhat dot com>]

On 18/09/17 10:58 -0700, Tim Shen via libstdc++ wrote:
> On Mon, Sep 18, 2017 at 10:26 AM, Jonathan Wakely <jwakely@redhat.com> wrote:
> > > We need to rewrite this to check the lengths are equal first, and then
> > > call the 3-argument version of std::equal.
> > >
> > > Alternatively, we could move the implementation of the C++14
> > > std::equal overloads to __equal and make that available for C++11.
> > > I'll try that.
> >
> >
> > Here's a proof of concept patch for that. It's a bit ugly.
>
> Instead of having iterator tags in the interface, we can probe the
> random-access-ness inside __equal4/__equal4_p, can't we? It's similar
> to the existing "if (_RAIters()) { ... }".
>
> I'd expect the patches to be renaming the current implementations and
> adding wrappers, instead of adding new implementations.

Well I decided to split the existing functions up and use tag
dispatching, which is conceptually cleaner anyway. But as the
RandomAccessIterator version doesn't need any operations that aren't
valid for other categories, it's not strictly necessary. The tag
dispatching version should generate slightly smaller code for
unoptimized builds, but that's not very important.

Here's the patch doing it as you suggest. We can't call the new
functions __equal because t hat name is already taken by a helper
struct, hence __equal4.

Do you prefer this version?


diff --git a/libstdc++-v3/include/bits/regex_executor.tcc b/libstdc++-v3/include/bits/regex_executor.tcc
index f6149fecf9d..2ceba35e7b8 100644
--- a/libstdc++-v3/include/bits/regex_executor.tcc
+++ b/libstdc++-v3/include/bits/regex_executor.tcc
@@ -366,17 +366,17 @@ namespace __detail
 	       _BiIter __actual_end)
       {
 	if (!_M_icase)
-	  return std::equal(__expected_begin, __expected_end,
-			    __actual_begin, __actual_end);
+	  return std::__equal4(__expected_begin, __expected_end,
+			       __actual_begin, __actual_end);
 	typedef std::ctype<_CharT> __ctype_type;
 	const auto& __fctyp = use_facet<__ctype_type>(_M_traits.getloc());
-	return std::equal(__expected_begin, __expected_end,
-			  __actual_begin, __actual_end,
-			  [this, &__fctyp](_CharT __lhs, _CharT __rhs)
-			  {
-			    return __fctyp.tolower(__lhs)
-				== __fctyp.tolower(__rhs);
-			  });
+	return std::__equal4(__expected_begin, __expected_end,
+			     __actual_begin, __actual_end,
+			     [this, &__fctyp](_CharT __lhs, _CharT __rhs)
+			     {
+			       return __fctyp.tolower(__lhs)
+				 == __fctyp.tolower(__rhs);
+			     });
       }
 
       bool _M_icase;
diff --git a/libstdc++-v3/include/bits/stl_algobase.h b/libstdc++-v3/include/bits/stl_algobase.h
index f68ecb22b82..ff5e94d9ae8 100644
--- a/libstdc++-v3/include/bits/stl_algobase.h
+++ b/libstdc++-v3/include/bits/stl_algobase.h
@@ -1082,6 +1082,58 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
       return true;
     }
 
+#if __cplusplus >= 201103L
+  template<typename _II1, typename _II2>
+    inline bool
+    __equal4(_II1 __first1, _II1 __last1, _II2 __first2, _II2 __last2)
+    {
+      using _RATag = random_access_iterator_tag;
+      using _Cat1 = typename iterator_traits<_II1>::iterator_category;
+      using _Cat2 = typename iterator_traits<_II2>::iterator_category;
+      using _RAIters = __and_<is_same<_Cat1, _RATag>, is_same<_Cat2, _RATag>>;
+      if (_RAIters())
+	{
+	  auto __d1 = std::distance(__first1, __last1);
+	  auto __d2 = std::distance(__first2, __last2);
+	  if (__d1 != __d2)
+	    return false;
+	  return _GLIBCXX_STD_A::equal(__first1, __last1, __first2);
+	}
+
+      for (; __first1 != __last1 && __first2 != __last2;
+	  ++__first1, (void)++__first2)
+	if (!(*__first1 == *__first2))
+	  return false;
+      return __first1 == __last1 && __first2 == __last2;
+    }
+
+  template<typename _II1, typename _II2, typename _BinaryPredicate>
+    inline bool
+    __equal4(_II1 __first1, _II1 __last1, _II2 __first2, _II2 __last2,
+	     _BinaryPredicate __binary_pred)
+    {
+      using _RATag = random_access_iterator_tag;
+      using _Cat1 = typename iterator_traits<_II1>::iterator_category;
+      using _Cat2 = typename iterator_traits<_II2>::iterator_category;
+      using _RAIters = __and_<is_same<_Cat1, _RATag>, is_same<_Cat2, _RATag>>;
+      if (_RAIters())
+	{
+	  auto __d1 = std::distance(__first1, __last1);
+	  auto __d2 = std::distance(__first2, __last2);
+	  if (__d1 != __d2)
+	    return false;
+	  return _GLIBCXX_STD_A::equal(__first1, __last1, __first2,
+				       __binary_pred);
+	}
+
+      for (; __first1 != __last1 && __first2 != __last2;
+	  ++__first1, (void)++__first2)
+	if (!bool(__binary_pred(*__first1, *__first2)))
+	  return false;
+      return __first1 == __last1 && __first2 == __last2;
+    }
+#endif // C++11
+
 #if __cplusplus > 201103L
 
 #define __cpp_lib_robust_nonmodifying_seq_ops 201304
@@ -1112,24 +1164,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
       __glibcxx_requires_valid_range(__first1, __last1);
       __glibcxx_requires_valid_range(__first2, __last2);
 
-      using _RATag = random_access_iterator_tag;
-      using _Cat1 = typename iterator_traits<_II1>::iterator_category;
-      using _Cat2 = typename iterator_traits<_II2>::iterator_category;
-      using _RAIters = __and_<is_same<_Cat1, _RATag>, is_same<_Cat2, _RATag>>;
-      if (_RAIters())
-	{
-	  auto __d1 = std::distance(__first1, __last1);
-	  auto __d2 = std::distance(__first2, __last2);
-	  if (__d1 != __d2)
-	    return false;
-	  return _GLIBCXX_STD_A::equal(__first1, __last1, __first2);
-	}
-
-      for (; __first1 != __last1 && __first2 != __last2;
-	  ++__first1, (void)++__first2)
-	if (!(*__first1 == *__first2))
-	  return false;
-      return __first1 == __last1 && __first2 == __last2;
+      return _GLIBCXX_STD_A::__equal4(__first1, __last1, __first2, __last2);
     }
 
   /**
@@ -1159,27 +1194,10 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
       __glibcxx_requires_valid_range(__first1, __last1);
       __glibcxx_requires_valid_range(__first2, __last2);
 
-      using _RATag = random_access_iterator_tag;
-      using _Cat1 = typename iterator_traits<_IIter1>::iterator_category;
-      using _Cat2 = typename iterator_traits<_IIter2>::iterator_category;
-      using _RAIters = __and_<is_same<_Cat1, _RATag>, is_same<_Cat2, _RATag>>;
-      if (_RAIters())
-	{
-	  auto __d1 = std::distance(__first1, __last1);
-	  auto __d2 = std::distance(__first2, __last2);
-	  if (__d1 != __d2)
-	    return false;
-	  return _GLIBCXX_STD_A::equal(__first1, __last1, __first2,
-				       __binary_pred);
-	}
-
-      for (; __first1 != __last1 && __first2 != __last2;
-	  ++__first1, (void)++__first2)
-	if (!bool(__binary_pred(*__first1, *__first2)))
-	  return false;
-      return __first1 == __last1 && __first2 == __last2;
+      return _GLIBCXX_STD_A::__equal4(__first1, __last1, __first2, __last2,
+				      __binary_pred);
     }
-#endif
+#endif // C++14
 
   /**
    *  @brief Performs @b dictionary comparison on ranges.