[libcxx-commits] [libcxx] [libc++] Fix possible out of range access in bitset (PR #121348)

[Peng Liu via libcxx-commits]

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@@ -283,21 +287,30 @@ inline _LIBCPP_HIDE_FROM_ABI void __bitset<_N_words, _Size>::__init(unsigned lon
 template <size_t _N_words, size_t _Size>
 inline _LIBCPP_CONSTEXPR __bitset<_N_words, _Size>::__bitset(unsigned long long __v) _NOEXCEPT
 #  ifndef _LIBCPP_CXX03_LANG
-#    if __SIZEOF_SIZE_T__ == 8
-    : __first_{__v}
-#    elif __SIZEOF_SIZE_T__ == 4
+#    if (__SIZEOF_LONG_LONG__ + __SIZEOF_SIZE_T__ - 1) / __SIZEOF_SIZE_T__ == 1
+    : __first_{static_cast<__storage_type>(__v)}
+#    elif (__SIZEOF_LONG_LONG__ + __SIZEOF_SIZE_T__ - 1) / __SIZEOF_SIZE_T__ == 2
+    : __first_{static_cast<__storage_type>(__v), static_cast<__storage_type>(__v >> __bits_per_word)}
+#    elif (__SIZEOF_LONG_LONG__ + __SIZEOF_SIZE_T__ - 1) / __SIZEOF_SIZE_T__ == 4
+#      if _N_words == 2
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winner245 wrote:

Thanks for correcting me! To address this, I have used SFINAE to dispatch based on the value of `_N_words` in C++11, as you suggested. However, for `>= C++14`, I opted for pack expansion with `index_sequence` to simplify the implementation (since `index_sequence` is not available in C++11).  

https://github.com/llvm/llvm-project/pull/121348