Simplify __bitset::__init

Author: winner245

libcxx/include/bitset

@@ -253,17 +253,14 @@ inline _LIBCPP_CONSTEXPR __bitset<_N_words, _Size>::__bitset() _NOEXCEPT
 
 template <size_t _N_words, size_t _Size>
 void __bitset<_N_words, _Size>::__init(unsigned long long __v, false_type) _NOEXCEPT {
-  __storage_type __t[sizeof(unsigned long long) / sizeof(__storage_type)];
-  size_t __sz = _Size;
-  for (size_t __i = 0; __i < sizeof(__t) / sizeof(__t[0]); ++__i, __v >>= __bits_per_word, __sz -= __bits_per_word)
+  size_t __ull = sizeof(unsigned long long) / sizeof(__storage_type);
+  for (size_t __i = 0, __sz = _Size; __i < __ull; ++__i, __v >>= __bits_per_word, __sz -= __bits_per_word)
     if (__sz < __bits_per_word)
-      __t[__i] = static_cast<__storage_type>(__v) & (1ULL << __sz) - 1;
+      __first_[__i] = static_cast<__storage_type>(__v) & (1ULL << __sz) - 1;
     else
-      __t[__i] = static_cast<__storage_type>(__v);
+      __first_[__i] = static_cast<__storage_type>(__v);
 
-  std::copy(__t, __t + sizeof(__t) / sizeof(__t[0]), __first_);
-  std::fill(
-      __first_ + sizeof(__t) / sizeof(__t[0]), __first_ + sizeof(__first_) / sizeof(__first_[0]), __storage_type(0));
+  std::fill(__first_ + __ull, __first_ + _N_words, __storage_type(0));
 }
 
 template <size_t _N_words, size_t _Size>
@@ -272,7 +269,7 @@ inline _LIBCPP_HIDE_FROM_ABI void __bitset<_N_words, _Size>::__init(unsigned lon
   if (_Size < __bits_per_word)
     __first_[0] &= (1ULL << _Size) - 1;
 
-  std::fill(__first_ + 1, __first_ + sizeof(__first_) / sizeof(__first_[0]), __storage_type(0));
+  std::fill(__first_ + 1, __first_ + _N_words, __storage_type(0));
 }
 
 #  endif // _LIBCPP_CXX03_LANG