Export of internal Abseil changes

--
d6e582e21ceec768aa72e857c10ba80cad2f2202 by Abseil Team <absl-team@google.com>:

adds bounds-checking for the second range in absl::c_mismatch

The API for the two-range absl::c_mismatch is misleading as it
doesn't check the bounds of the second range against the first one.
This commit cleans up the internals of the overload to make sure that
buggy calls are not exploitable; non-buggy calls are unaffected.

This is consistent with both C++14's two-range std::mismatch and
C++20's std::ranges::mismatch (see http://wg21.link/mismatch).

PiperOrigin-RevId: 335050236
GitOrigin-RevId: d6e582e21ceec768aa72e857c10ba80cad2f2202
Change-Id: I77e0d030adf35c09069ceab5ea67efdf09377390

1 files changed, 29 insertions, 10 deletions

diff --git a/absl/algorithm/container.h b/absl/algorithm/container.h
index 5c033571..7778ab17 100644
--- a/absl/algorithm/container.h
+++ b/absl/algorithm/container.h
@@ -340,24 +340,43 @@ container_algorithm_internal::ContainerDifferenceType<const C> c_count_if(
 // c_mismatch()
 //
 // Container-based version of the <algorithm> `std::mismatch()` function to
-// return the first element where two ordered containers differ.
+// return the first element where two ordered containers differ. Applies `==` to
+// the first N elements of `c1` and `c2`, where N = min(size(c1), size(c2)).
 template <typename C1, typename C2>
 container_algorithm_internal::ContainerIterPairType<C1, C2>
 c_mismatch(C1& c1, C2& c2) {
-  return std::mismatch(container_algorithm_internal::c_begin(c1),
-                       container_algorithm_internal::c_end(c1),
-                       container_algorithm_internal::c_begin(c2));
+  auto first1 = container_algorithm_internal::c_begin(c1);
+  auto last1 = container_algorithm_internal::c_end(c1);
+  auto first2 = container_algorithm_internal::c_begin(c2);
+  auto last2 = container_algorithm_internal::c_end(c2);
+
+  for (; first1 != last1 && first2 != last2; ++first1, (void)++first2) {
+    if (*first1 != *first2) {
+      break;
+    }
+  }
+
+  return std::make_pair(first1, first2);
 }
 
 // Overload of c_mismatch() for using a predicate evaluation other than `==` as
-// the function's test condition.
+// the function's test condition. Applies `pred`to the first N elements of `c1`
+// and `c2`, where N = min(size(c1), size(c2)).
 template <typename C1, typename C2, typename BinaryPredicate>
 container_algorithm_internal::ContainerIterPairType<C1, C2>
-c_mismatch(C1& c1, C2& c2, BinaryPredicate&& pred) {
-  return std::mismatch(container_algorithm_internal::c_begin(c1),
-                       container_algorithm_internal::c_end(c1),
-                       container_algorithm_internal::c_begin(c2),
-                       std::forward<BinaryPredicate>(pred));
+c_mismatch(C1& c1, C2& c2, BinaryPredicate pred) {
+  auto first1 = container_algorithm_internal::c_begin(c1);
+  auto last1 = container_algorithm_internal::c_end(c1);
+  auto first2 = container_algorithm_internal::c_begin(c2);
+  auto last2 = container_algorithm_internal::c_end(c2);
+
+  for (; first1 != last1 && first2 != last2; ++first1, (void)++first2) {
+    if (!pred(*first1, *first2)) {
+      break;
+    }
+  }
+
+  return std::make_pair(first1, first2);
 }
 
 // c_equal()