[libcxx-commits] [libcxx] [libc++] Fix wraparound issue with -fsanitize=integer in string operator>> (PR #106263)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: Louis Dionne (ldionne)

<details>
<summary>Changes</summary>

Fixes #<!-- -->106261
rdar://133991190

---
Full diff: https://github.com/llvm/llvm-project/pull/106263.diff


1 Files Affected:

- (modified) libcxx/include/istream (+6-6) 


``````````diff
diff --git a/libcxx/include/istream b/libcxx/include/istream
index d2b577a9ad9efc..84cb0ac9d9f252 100644
--- a/libcxx/include/istream
+++ b/libcxx/include/istream
@@ -1211,12 +1211,12 @@ operator>>(basic_istream<_CharT, _Traits>& __is, basic_string<_CharT, _Traits, _
     try {
 #endif
       __str.clear();
-      streamsize __n = __is.width();
-      if (__n <= 0)
-        __n = __str.max_size();
-      if (__n <= 0)
-        __n = numeric_limits<streamsize>::max();
-      streamsize __c            = 0;
+      using _Size = typename basic_string<_CharT, _Traits, _Allocator>::size_type;
+      static_assert(numeric_limits<_Size>::max() >= numeric_limits<streamsize>::max(),
+                    "Stream width could be too large to be represented in the string's size_type");
+      streamsize const __width  = __is.width();
+      _Size const __n           = __width <= 0 ? __str.max_size() : static_cast<_Size>(__width);
+      _Size __c                 = 0;
       const ctype<_CharT>& __ct = std::use_facet<ctype<_CharT> >(__is.getloc());
       while (__c < __n) {
         typename _Traits::int_type __i = __is.rdbuf()->sgetc();

``````````

</details>


https://github.com/llvm/llvm-project/pull/106263