Apply @frederick-vs-ja suggestions to support 16-bit platforms

Author: winner245

libcxx/include/bitset

@@ -233,6 +233,8 @@ private:
 #  endif // _LIBCPP_CXX03_LANG
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long to_ulong(false_type) const;
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long to_ulong(true_type) const;
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long to_ulong(true_type, false_type) const;
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long to_ulong(true_type, true_type) const;
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long long to_ullong(false_type) const;
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long long to_ullong(true_type) const;
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long long to_ullong(true_type, false_type) const;
@@ -281,14 +283,23 @@ 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
+    : __first_{static_cast<__storage_type>(__v), static_cast<__storage_type>(__v >> __bits_per_word)}
+#      elif _N_words == 3
     : __first_{static_cast<__storage_type>(__v),
-               _Size >= 2 * __bits_per_word
-                   ? static_cast<__storage_type>(__v >> __bits_per_word)
-                   : static_cast<__storage_type>((__v >> __bits_per_word) &
-                                                 (__storage_type(1) << (_Size - __bits_per_word)) - 1)}
+               static_cast<__storage_type>(__v >> __bits_per_word),
+               static_cast<__storage_type>(__v >> (__bits_per_word * 2))}
+#      else
+    : __first_{static_cast<__storage_type>(__v),
+               static_cast<__storage_type>(__v >> __bits_per_word),
+               static_cast<__storage_type>(__v >> (__bits_per_word * 2)),
+               static_cast<__storage_type>(__v >> (__bits_per_word * 3))}
+#      endif
 #    else
 #      error This constructor has not been ported to this platform
 #    endif
@@ -344,13 +355,30 @@ __bitset<_N_words, _Size>::to_ulong(false_type) const {
   if (__i != __e)
     __throw_overflow_error("bitset to_ulong overflow error");
 
-  return __first_[0];
+  return to_ulong(true_type());
 }
 
 template <size_t _N_words, size_t _Size>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long
 __bitset<_N_words, _Size>::to_ulong(true_type) const {
-  return __first_[0];
+  return to_ulong(true_type(), integral_constant<bool, sizeof(__storage_type) < sizeof(unsigned long)>());
+}
+
+template <size_t _N_words, size_t _Size>
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long
+__bitset<_N_words, _Size>::to_ulong(true_type, false_type) const {
+  return static_cast<unsigned long>(__first_[0]);
+}
+
+template <size_t _N_words, size_t _Size>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long
+__bitset<_N_words, _Size>::to_ulong(true_type, true_type) const {
+  unsigned long __r       = __first_[0];
+  const size_t __ul_words = sizeof(unsigned long) / sizeof(__storage_type);
+  const size_t __n        = _N_words < __ul_words ? _N_words : __ul_words;
+  for (size_t __i = 1; __i < __n; ++__i)
+    __r |= static_cast<unsigned long>(__first_[__i]) << (__bits_per_word * __i);
+  return __r;
 }
 
 template <size_t _N_words, size_t _Size>
@@ -373,7 +401,7 @@ __bitset<_N_words, _Size>::to_ullong(true_type) const {
 template <size_t _N_words, size_t _Size>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long long
 __bitset<_N_words, _Size>::to_ullong(true_type, false_type) const {
-  return __first_[0];
+  return static_cast<unsigned long long>(__first_[0]);
 }
 
 template <size_t _N_words, size_t _Size>
@@ -383,9 +411,9 @@ __bitset<_N_words, _Size>::to_ullong(true_type, true_type) const {
   _LIBCPP_DIAGNOSTIC_PUSH
   _LIBCPP_GCC_DIAGNOSTIC_IGNORED("-Wshift-count-overflow")
   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;
-  for (size_t __i = 1; __i < __n_words; ++__i)
-    __r |= static_cast<unsigned long long>(__first_[__i]) << (sizeof(__storage_type) * CHAR_BIT * __i);
+  const size_t __n         = _N_words < __ull_words ? _N_words : __ull_words;
+  for (size_t __i = 1; __i < __n; ++__i)
+    __r |= static_cast<unsigned long long>(__first_[__i]) << (__bits_per_word * __i);
   _LIBCPP_DIAGNOSTIC_POP
   return __r;
 }
@@ -494,8 +522,7 @@ inline _LIBCPP_CONSTEXPR __bitset<1, _Size>::__bitset() _NOEXCEPT : __first_(0)
 
 template <size_t _Size>
 inline _LIBCPP_CONSTEXPR __bitset<1, _Size>::__bitset(unsigned long long __v) _NOEXCEPT
-    : __first_(_Size == __bits_per_word ? static_cast<__storage_type>(__v)
-                                        : static_cast<__storage_type>(__v) & ((__storage_type(1) << _Size) - 1)) {}
+    : __first_(static_cast<__storage_type>(__v)) {}
 
 template <size_t _Size>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 void
@@ -524,12 +551,12 @@ inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 void __bitset<1, _Siz
 
 template <size_t _Size>
 inline _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long __bitset<1, _Size>::to_ulong() const {
-  return __first_;
+  return static_cast<unsigned long>(__first_);
 }
 
 template <size_t _Size>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long long __bitset<1, _Size>::to_ullong() const {
-  return __first_;
+  return static_cast<unsigned long long>(__first_);
 }
 
 template <size_t _Size>
@@ -595,8 +622,8 @@ protected:
 
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 void flip() _NOEXCEPT {}
 
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long to_ulong() const { return 0; }
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long long to_ullong() const { return 0; }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long to_ulong() const { return 0UL; }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 unsigned long long to_ullong() const { return 0ULL; }
 
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 bool all() const _NOEXCEPT { return true; }
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 bool any() const _NOEXCEPT { return false; }
@@ -626,7 +653,8 @@ public:
 
   // 23.3.5.1 constructors:
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR bitset() _NOEXCEPT {}
-  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR bitset(unsigned long long __v) _NOEXCEPT : __base(__v) {}
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR bitset(unsigned long long __v) _NOEXCEPT
+      : __base(sizeof(unsigned long long) * CHAR_BIT <= _Size ? __v : __v & ((1ULL << _Size) - 1)) {}
   template <class _CharT, __enable_if_t<_IsCharLikeType<_CharT>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 explicit bitset(
       const _CharT* __str,