[libc++] Added segmented iterator for std::equal

libcxx/include/__algorithm/equal.h

@@ -17,6 +17,7 @@
 #include <__functional/invoke.h>
 #include <__iterator/distance.h>
 #include <__iterator/iterator_traits.h>
+#include <__iterator/segmented_iterator.h>
 #include <__string/constexpr_c_functions.h>
 #include <__type_traits/desugars_to.h>
 #include <__type_traits/enable_if.h>
@@ -95,6 +96,81 @@ __equal_impl(_Tp* __first1, _Tp* __last1, _Up* __first2, _Up*, _Pred&, _Proj1&,
   return std::__constexpr_memcmp_equal(__first1, __first2, __element_count(__last1 - __first1));
 }
 
+template <class _SegmentedIterator1, class _SegmentedIterator2, class _BinaryPredicate, class _Proj1, class _Proj2>
+_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool __equal_segment(
+    _SegmentedIterator1 __first1,
+    _SegmentedIterator1 __last1,
+    _SegmentedIterator2 __first2,
+    _SegmentedIterator2 __last2,
+    _BinaryPredicate __pred,
+    _Proj1& __proj1,
+    _Proj2& __proj2) {
+  using _Traits1 = __segmented_iterator_traits<_SegmentedIterator1>;
+  using _Traits2 = __segmented_iterator_traits<_SegmentedIterator2>;
+
+  auto __sfirst1 = _Traits1::__segment(__first1);
+  auto __slast1  = _Traits1::__segment(__last1);
+
+  auto __sfirst2 = _Traits2::__segment(__first2);
+  auto __slast2  = _Traits2::__segment(__last2);
+
+  // Both have only 1 segment
+  if (__sfirst1 == __slast1 && __sfirst2 == __slast2)
+    return std::__equal_impl(
+        std::__unwrap_iter(_Traits1::__local(__first1)),
+        std::__unwrap_iter(_Traits1::__local(__last1)),
+        std::__unwrap_iter(_Traits2::__local(__first2)),
+        std::__unwrap_iter(_Traits2::__local(__last2)),
+        __pred,
+        __proj1,
+        __proj2);
+
+  { // We have more than one segment. Iterate over the first segment, since we might not start at the beginning
+    if (!std::__equal_impl(
+            std::__unwrap_iter(_Traits1::__local(__first1)),
+            std::__unwrap_iter(_Traits1::__end(__sfirst1)),
+            std::__unwrap_iter(_Traits2::__local(__first2)),
+            std::__unwrap_iter(_Traits2::__end(__sfirst2)),
+            __pred,
+            __proj1,
+            __proj2)) {
+      return false;
+    }
+  }
+  ++__sfirst1;
+  ++__sfirst2;
+
+  // Iterate over the segments which are guaranteed to be completely in the range
+  while (__sfirst1 != __slast1 && __sfirst2 != __slast2) {
+    if (!std::__equal_impl(
+            std::__unwrap_iter(_Traits1::__begin(__sfirst1)),
+            std::__unwrap_iter(_Traits1::__end(__sfirst1)),
+            std::__unwrap_iter(_Traits2::__begin(__sfirst2)),
+            std::__unwrap_iter(_Traits2::__end(__sfirst2)),
+            __pred,
+            __proj1,
+            __proj2)) {
+      return false;
+    }
+    ++__sfirst1;
+    ++__sfirst2;
+  }
+
+  // Iterate over the last segment
+  if (!std::__equal_impl(
+          std::__unwrap_iter(_Traits1::__begin(__sfirst1)),
+          std::__unwrap_iter(_Traits1::__local(__last1)),
+          std::__unwrap_iter(_Traits2::__begin(__sfirst2)),
+          std::__unwrap_iter(_Traits2::__local(__last2)),
+          __pred,
+          __proj1,
+          __proj2)) {
+    return false;
+  }
+
+  return __sfirst1 == __slast1 && __sfirst2 == __slast2;
+}
+
 template <class _InputIterator1, class _InputIterator2, class _BinaryPredicate>
 _LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 equal(_InputIterator1 __first1,
@@ -108,6 +184,11 @@ equal(_InputIterator1 __first1,
       return false;
   }
   __identity __proj;
+
+  if constexpr (__is_segmented_iterator<_InputIterator1>::value && __is_segmented_iterator<_InputIterator2>::value) {
+    return std::__equal_segment(__first1, __last1, __first2, __last2, __pred, __proj, __proj);
+  }
+
   return std::__equal_impl(
       std::__unwrap_iter(__first1),
       std::__unwrap_iter(__last1),