Add P0553R4 and P0556R3 to <bit> (with D1956 rename) (#310)

Resolves #25 and resolves #26. Currently active for Clang and EDG, but not C1XX.

stl/inc/bit

@@ -12,6 +12,9 @@
 #pragma message("The contents of <bit> are available only with C++20 or later.")
 #else // ^^^ !_HAS_CXX20 / _HAS_CXX20 vvv
 
+#include <limits>
+#include <type_traits>
+
 #pragma pack(push, _CRT_PACKING)
 #pragma warning(push, _STL_WARNING_LEVEL)
 #pragma warning(disable : _STL_DISABLED_WARNINGS)
@@ -22,6 +25,121 @@ _STL_DISABLE_CLANG_WARNINGS
 _STD_BEGIN
 enum class endian { little = 0, big = 1, native = little };
 
+#ifdef __cpp_lib_bitops // TRANSITION, VSO-1020212
+template <class _Ty>
+inline constexpr bool _Is_standard_unsigned_integer =
+    _Is_any_of_v<remove_cv_t<_Ty>, unsigned char, unsigned short, unsigned int, unsigned long, unsigned long long>;
+
+
+template <class _Ty, enable_if_t<_Is_standard_unsigned_integer<_Ty>, int> = 0>
+_NODISCARD constexpr int countl_zero(_Ty _Val) noexcept;
+
+template <class _Ty, enable_if_t<_Is_standard_unsigned_integer<_Ty>, int> = 0>
+_NODISCARD constexpr bool ispow2(const _Ty _Val) noexcept {
+    return _Val != 0 && (_Val & (_Val - 1)) == 0;
+}
+
+template <class _Ty, enable_if_t<_Is_standard_unsigned_integer<_Ty>, int> = 0>
+_NODISCARD constexpr _Ty ceil2(const _Ty _Val) noexcept /* strengthened */ {
+    if (_Val == 0) {
+        return 1;
+    }
+
+    return static_cast<_Ty>(_Ty{1} << (numeric_limits<_Ty>::digits - _STD countl_zero(static_cast<_Ty>(_Val - 1))));
+}
+
+template <class _Ty, enable_if_t<_Is_standard_unsigned_integer<_Ty>, int> = 0>
+_NODISCARD constexpr _Ty floor2(const _Ty _Val) noexcept {
+    if (_Val == 0) {
+        return 0;
+    }
+
+    return static_cast<_Ty>(_Ty{1} << (numeric_limits<_Ty>::digits - 1 - _STD countl_zero(_Val)));
+}
+
+template <class _Ty, enable_if_t<_Is_standard_unsigned_integer<_Ty>, int> = 0>
+_NODISCARD constexpr _Ty bit_length(const _Ty _Val) noexcept {
+    return static_cast<_Ty>(numeric_limits<_Ty>::digits - _STD countl_zero(_Val));
+}
+
+template <class _Ty, enable_if_t<_Is_standard_unsigned_integer<_Ty>, int> = 0>
+_NODISCARD constexpr _Ty rotr(_Ty _Val, int _Rotation) noexcept;
+
+template <class _Ty, enable_if_t<_Is_standard_unsigned_integer<_Ty>, int> = 0>
+_NODISCARD constexpr _Ty rotl(const _Ty _Val, const int _Rotation) noexcept {
+    constexpr auto _Digits = numeric_limits<_Ty>::digits;
+    const auto _Remainder  = _Rotation % _Digits;
+    if (_Remainder > 0) {
+        return static_cast<_Ty>(
+            static_cast<_Ty>(_Val << _Remainder) | static_cast<_Ty>(_Val >> (_Digits - _Remainder)));
+    } else if (_Remainder == 0) {
+        return _Val;
+    } else { // _Remainder < 0
+        return _STD rotr(_Val, -_Remainder);
+    }
+}
+
+template <class _Ty, enable_if_t<_Is_standard_unsigned_integer<_Ty>, int> _Enabled>
+_NODISCARD constexpr _Ty rotr(const _Ty _Val, const int _Rotation) noexcept {
+    constexpr auto _Digits = numeric_limits<_Ty>::digits;
+    const auto _Remainder  = _Rotation % _Digits;
+    if (_Remainder > 0) {
+        return static_cast<_Ty>(
+            static_cast<_Ty>(_Val >> _Remainder) | static_cast<_Ty>(_Val << (_Digits - _Remainder)));
+    } else if (_Remainder == 0) {
+        return _Val;
+    } else { // _Remainder < 0
+        return _STD rotl(_Val, -_Remainder);
+    }
+}
+
+template <class _Ty, enable_if_t<_Is_standard_unsigned_integer<_Ty>, int> _Enabled>
+_NODISCARD constexpr int countl_zero(const _Ty _Val) noexcept {
+    constexpr int _Digits = numeric_limits<_Ty>::digits;
+    if (_Val == 0) {
+        return _Digits;
+    }
+
+    if constexpr (sizeof(_Ty) <= sizeof(unsigned int)) {
+        return __builtin_clz(_Val) - (numeric_limits<unsigned int>::digits - _Digits);
+    } else {
+        return __builtin_clzll(_Val) - (numeric_limits<unsigned long long>::digits - _Digits);
+    }
+}
+
+template <class _Ty, enable_if_t<_Is_standard_unsigned_integer<_Ty>, int> = 0>
+_NODISCARD constexpr int countl_one(const _Ty _Val) noexcept {
+    return _STD countl_zero(static_cast<_Ty>(~_Val));
+}
+
+template <class _Ty, enable_if_t<_Is_standard_unsigned_integer<_Ty>, int> = 0>
+_NODISCARD constexpr int countr_zero(const _Ty _Val) noexcept {
+    if (_Val == 0) {
+        return numeric_limits<_Ty>::digits;
+    }
+
+    if constexpr (sizeof(_Ty) <= sizeof(unsigned int)) {
+        return __builtin_ctz(_Val);
+    } else {
+        return __builtin_ctzll(_Val);
+    }
+}
+
+template <class _Ty, enable_if_t<_Is_standard_unsigned_integer<_Ty>, int> _Enabled = 0>
+_NODISCARD constexpr int countr_one(const _Ty _Val) noexcept {
+    return _STD countr_zero(static_cast<_Ty>(~_Val));
+}
+
+template <class _Ty, enable_if_t<_Is_standard_unsigned_integer<_Ty>, int> _Enabled = 0>
+_NODISCARD constexpr int popcount(const _Ty _Val) noexcept {
+    if constexpr (sizeof(_Ty) <= sizeof(unsigned int)) {
+        return __builtin_popcount(_Val);
+    } else {
+        return __builtin_popcountll(_Val);
+    }
+}
+#endif // __cpp_lib_bitops
+
 _STD_END
 
 #pragma pop_macro("new")

stl/inc/yvals_core.h

@@ -31,6 +31,9 @@
 //     (mbrtoc8 and c8rtomb not yet implemented)
 // P0487R1 Fixing operator>>(basic_istream&, CharT*)
 // P0550R2 remove_cvref
+// P0553R4 <bit> Rotating And Counting Functions
+// P0556R3 <bit> ispow2(), ceil2(), floor2(), log2p1()
+//            (log2p1() is called bit_length() as of D1956)
 // P0616R0 Using move() In <numeric>
 // P0631R8 <numbers> Math Constants
 // P0646R1 list/forward_list remove()/remove_if()/unique() Return size_type
@@ -945,7 +948,13 @@
 
 // C++20
 #if _HAS_CXX20
-#define __cpp_lib_bind_front           201907L
+#define __cpp_lib_bind_front 201907L
+#if defined(__clang__) || defined(__EDG__)
+#define __cpp_lib_bitops 201907L
+#else // ^^^ Clang and EDG / MSVC vvv
+// a future MSVC update will embed CPU feature detection into <bit> intrinsics
+// TRANSITION, VSO-1020212
+#endif // defined(__clang__) || defined(__EDG__)
 #define __cpp_lib_bounded_array_traits 201902L
 #ifdef __cpp_char8_t
 #define __cpp_lib_char8_t 201811L