[libcxx-commits] [libcxx] [libc++] Improve bitset::to_ullong Implementation (PR #121348)

[A. Jiang via libcxx-commits]

================
@@ -381,8 +382,9 @@ __bitset<_N_words, _Size>::to_ullong(true_type, true_type) const {
   unsigned long long __r = __first_[0];
   _LIBCPP_DIAGNOSTIC_PUSH
   _LIBCPP_GCC_DIAGNOSTIC_IGNORED("-Wshift-count-overflow")
-  for (size_t __i = 1; __i < sizeof(unsigned long long) / sizeof(__storage_type); ++__i)
-    __r |= static_cast<unsigned long long>(__first_[__i]) << (sizeof(__storage_type) * CHAR_BIT);
+  size_t __n_words = std::min<size_t>(_N_words, sizeof(unsigned long long) / sizeof(__storage_type));
----------------
frederick-vs-ja wrote:

I think we want the newly introduced `__n_words` to be a constant expression.

How about this?

```suggestion
  const size_t __ull_words = sizeof(unsigned long long) / sizeof(__storage_type);
  const size_t __n_words   = _N_words < __ull_words ? _N_words : __ull_words;
```

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