include/__string/constexpr_c_functions.h - llvm-project/libcxx - Git at Google

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//

 #ifndef _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H
 #define _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H

 #include <__config>
 #include <__memory/addressof.h>
 #include <__memory/construct_at.h>
 #include <__type_traits/datasizeof.h>
 #include <__type_traits/is_always_bitcastable.h>
 #include <__type_traits/is_assignable.h>
 #include <__type_traits/is_constant_evaluated.h>
 #include <__type_traits/is_constructible.h>
 #include <__type_traits/is_equality_comparable.h>
 #include <__type_traits/is_same.h>
 #include <__type_traits/is_trivially_copyable.h>
 #include <__type_traits/is_trivially_lexicographically_comparable.h>
 #include <__type_traits/remove_cv.h>
 #include <__utility/is_pointer_in_range.h>
 #include <cstddef>

 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif

 _LIBCPP_BEGIN_NAMESPACE_STD

 // Type used to encode that a function takes an integer that represents a number
 // of elements as opposed to a number of bytes.
 enum class __element_count : size_t {};

 template <class _Tp>
 inline const bool __is_char_type = false;

 template <>
 inline const bool __is_char_type<char> = true;

 #ifndef _LIBCPP_HAS_NO_CHAR8_T
 template <>
 inline const bool __is_char_type<char8_t> = true;
 #endif

 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 size_t __constexpr_strlen(const _Tp* __str) _NOEXCEPT {
   static_assert(__is_char_type<_Tp>, "__constexpr_strlen only works with char and char8_t");
   // GCC currently doesn't support __builtin_strlen for heap-allocated memory during constant evaluation.
   // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70816
   if (__libcpp_is_constant_evaluated()) {
 #if _LIBCPP_STD_VER >= 17 && defined(_LIBCPP_COMPILER_CLANG_BASED)
     if constexpr (is_same_v<_Tp, char>)
       return __builtin_strlen(__str);
 #endif
     size_t __i = 0;
     for (; __str[__i] != '\0'; ++__i)
       ;
     return __i;
   }
   return __builtin_strlen(reinterpret_cast<const char*>(__str));
 }

 // Because of __libcpp_is_trivially_lexicographically_comparable we know that comparing the object representations is
 // equivalent to a std::memcmp. Since we have multiple objects contiguously in memory, we can call memcmp once instead
 // of invoking it on every object individually.
 template <class _Tp, class _Up>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int
 __constexpr_memcmp(const _Tp* __lhs, const _Up* __rhs, __element_count __n) {
   static_assert(__libcpp_is_trivially_lexicographically_comparable<_Tp, _Up>::value,
                 "_Tp and _Up have to be trivially lexicographically comparable");

   auto __count = static_cast<size_t>(__n);

   if (__libcpp_is_constant_evaluated()) {
 #ifdef _LIBCPP_COMPILER_CLANG_BASED
     if (sizeof(_Tp) == 1 && !is_same<_Tp, bool>::value)
       return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp));
 #endif

     while (__count != 0) {
       if (*__lhs < *__rhs)
         return -1;
       if (*__rhs < *__lhs)
         return 1;

       --__count;
       ++__lhs;
       ++__rhs;
     }
     return 0;
   } else {
     return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp));
   }
 }

 // Because of __libcpp_is_trivially_equality_comparable we know that comparing the object representations is equivalent
 // to a std::memcmp(...) == 0. Since we have multiple objects contiguously in memory, we can call memcmp once instead
 // of invoking it on every object individually.
 template <class _Tp, class _Up>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool
 __constexpr_memcmp_equal(const _Tp* __lhs, const _Up* __rhs, __element_count __n) {
   static_assert(__libcpp_is_trivially_equality_comparable<_Tp, _Up>::value,
                 "_Tp and _Up have to be trivially equality comparable");

   auto __count = static_cast<size_t>(__n);

   if (__libcpp_is_constant_evaluated()) {
 #ifdef _LIBCPP_COMPILER_CLANG_BASED
     if (sizeof(_Tp) == 1 && is_integral<_Tp>::value && !is_same<_Tp, bool>::value)
       return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)) == 0;
 #endif
     while (__count != 0) {
       if (*__lhs != *__rhs)
         return false;

       --__count;
       ++__lhs;
       ++__rhs;
     }
     return true;
   } else {
     return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)) == 0;
   }
 }

 template <class _Tp, class _Up>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp* __constexpr_memchr(_Tp* __str, _Up __value, size_t __count) {
   static_assert(sizeof(_Tp) == 1 && __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value,
                 "Calling memchr on non-trivially equality comparable types is unsafe.");

   if (__libcpp_is_constant_evaluated()) {
 // use __builtin_char_memchr to optimize constexpr evaluation if we can
 #if _LIBCPP_STD_VER >= 17 && __has_builtin(__builtin_char_memchr)
     if constexpr (is_same_v<remove_cv_t<_Tp>, char> && is_same_v<remove_cv_t<_Up>, char>)
       return __builtin_char_memchr(__str, __value, __count);
 #endif

     for (; __count; --__count) {
       if (*__str == __value)
         return __str;
       ++__str;
     }
     return nullptr;
   } else {
     char __value_buffer = 0;
     __builtin_memcpy(&__value_buffer, &__value, sizeof(char));
     return static_cast<_Tp*>(__builtin_memchr(__str, __value_buffer, __count));
   }
 }

 // This function performs an assignment to an existing, already alive TriviallyCopyable object
 // from another TriviallyCopyable object.
 //
 // It basically works around the fact that TriviallyCopyable objects are not required to be
 // syntactically copy/move constructible or copy/move assignable. Technically, only one of the
 // four operations is required to be syntactically valid -- but at least one definitely has to
 // be valid.
 //
 // This is necessary in order to implement __constexpr_memmove below in a way that mirrors as
 // closely as possible what the compiler's __builtin_memmove is able to do.
 template <class _Tp, class _Up, __enable_if_t<is_assignable<_Tp&, _Up const&>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up const& __src) {
   __dest = __src;
   return __dest;
 }

 // clang-format off
 template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value &&
                                                is_assignable<_Tp&, _Up&&>::value, int> = 0>
 // clang-format on
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up& __src) {
   __dest =
       static_cast<_Up&&>(__src); // this is safe, we're not actually moving anything since the assignment is trivial
   return __dest;
 }

 // clang-format off
 template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value &&
                                               !is_assignable<_Tp&, _Up&&>::value &&
                                                is_constructible<_Tp, _Up const&>::value, int> = 0>
 // clang-format on
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up const& __src) {
   // _Tp is trivially destructible, so we don't need to call its destructor to end the lifetime of the object
   // that was there previously
   std::__construct_at(std::addressof(__dest), __src);
   return __dest;
 }

 // clang-format off
 template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value &&
                                               !is_assignable<_Tp&, _Up&&>::value &&
                                               !is_constructible<_Tp, _Up const&>::value &&
                                                is_constructible<_Tp, _Up&&>::value, int> = 0>
 // clang-format on
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up& __src) {
   // _Tp is trivially destructible, so we don't need to call its destructor to end the lifetime of the object
   // that was there previously
   std::__construct_at(
       std::addressof(__dest),
       static_cast<_Up&&>(__src)); // this is safe, we're not actually moving anything since the constructor is trivial
   return __dest;
 }

 template <class _Tp, class _Up, __enable_if_t<__is_always_bitcastable<_Up, _Tp>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp*
 __constexpr_memmove(_Tp* __dest, _Up* __src, __element_count __n) {
   size_t __count = static_cast<size_t>(__n);
   if (__libcpp_is_constant_evaluated()) {
 #ifdef _LIBCPP_COMPILER_CLANG_BASED
     if (is_same<__remove_cv_t<_Tp>, __remove_cv_t<_Up> >::value) {
       ::__builtin_memmove(__dest, __src, __count * sizeof(_Tp));
       return __dest;
     }
 #endif
     if (std::__is_pointer_in_range(__src, __src + __count, __dest)) {
       for (; __count > 0; --__count)
         std::__assign_trivially_copyable(__dest[__count - 1], __src[__count - 1]);
     } else {
       for (size_t __i = 0; __i != __count; ++__i)
         std::__assign_trivially_copyable(__dest[__i], __src[__i]);
     }
   } else if (__count > 0) {
     ::__builtin_memmove(__dest, __src, (__count - 1) * sizeof(_Tp) + __datasizeof_v<_Tp>);
   }
   return __dest;
 }

 _LIBCPP_END_NAMESPACE_STD

 #endif // _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H
	//===----------------------------------------------------------------------===//
	//
	// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
	// See https://llvm.org/LICENSE.txt for license information.
	// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
	//
	//===----------------------------------------------------------------------===//

	#ifndef _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H
	#define _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H

	#include <__config>
	#include <__memory/addressof.h>
	#include <__memory/construct_at.h>
	#include <__type_traits/datasizeof.h>
	#include <__type_traits/is_always_bitcastable.h>
	#include <__type_traits/is_assignable.h>
	#include <__type_traits/is_constant_evaluated.h>
	#include <__type_traits/is_constructible.h>
	#include <__type_traits/is_equality_comparable.h>
	#include <__type_traits/is_same.h>
	#include <__type_traits/is_trivially_copyable.h>
	#include <__type_traits/is_trivially_lexicographically_comparable.h>
	#include <__type_traits/remove_cv.h>
	#include <__utility/is_pointer_in_range.h>
	#include <cstddef>

	#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
	# pragma GCC system_header
	#endif

	_LIBCPP_BEGIN_NAMESPACE_STD

	// Type used to encode that a function takes an integer that represents a number
	// of elements as opposed to a number of bytes.
	enum class __element_count : size_t {};

	template <class _Tp>
	inline const bool __is_char_type = false;

	template <>
	inline const bool __is_char_type<char> = true;

	#ifndef _LIBCPP_HAS_NO_CHAR8_T
	template <>
	inline const bool __is_char_type<char8_t> = true;
	#endif

	template <class _Tp>
	inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 size_t __constexpr_strlen(const _Tp* __str) _NOEXCEPT {
	static_assert(__is_char_type<_Tp>, "__constexpr_strlen only works with char and char8_t");
	// GCC currently doesn't support __builtin_strlen for heap-allocated memory during constant evaluation.
	// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70816
	if (__libcpp_is_constant_evaluated()) {
	#if _LIBCPP_STD_VER >= 17 && defined(_LIBCPP_COMPILER_CLANG_BASED)
	if constexpr (is_same_v<_Tp, char>)
	return __builtin_strlen(__str);
	#endif
	size_t __i = 0;
	for (; __str[__i] != '\0'; ++__i)
	;
	return __i;
	}
	return __builtin_strlen(reinterpret_cast<const char*>(__str));
	}

	// Because of __libcpp_is_trivially_lexicographically_comparable we know that comparing the object representations is
	// equivalent to a std::memcmp. Since we have multiple objects contiguously in memory, we can call memcmp once instead
	// of invoking it on every object individually.
	template <class _Tp, class _Up>
	_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int
	__constexpr_memcmp(const _Tp* __lhs, const _Up* __rhs, __element_count __n) {
	static_assert(__libcpp_is_trivially_lexicographically_comparable<_Tp, _Up>::value,
	"_Tp and _Up have to be trivially lexicographically comparable");

	auto __count = static_cast<size_t>(__n);

	if (__libcpp_is_constant_evaluated()) {
	#ifdef _LIBCPP_COMPILER_CLANG_BASED
	if (sizeof(_Tp) == 1 && !is_same<_Tp, bool>::value)
	return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp));
	#endif

	while (__count != 0) {
	if (__lhs < __rhs)
	return -1;
	if (__rhs < __lhs)
	return 1;

	--__count;
	++__lhs;
	++__rhs;
	}
	return 0;
	} else {
	return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp));
	}
	}

	// Because of __libcpp_is_trivially_equality_comparable we know that comparing the object representations is equivalent
	// to a std::memcmp(...) == 0. Since we have multiple objects contiguously in memory, we can call memcmp once instead
	// of invoking it on every object individually.
	template <class _Tp, class _Up>
	_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool
	__constexpr_memcmp_equal(const _Tp* __lhs, const _Up* __rhs, __element_count __n) {
	static_assert(__libcpp_is_trivially_equality_comparable<_Tp, _Up>::value,
	"_Tp and _Up have to be trivially equality comparable");

	auto __count = static_cast<size_t>(__n);

	if (__libcpp_is_constant_evaluated()) {
	#ifdef _LIBCPP_COMPILER_CLANG_BASED
	if (sizeof(_Tp) == 1 && is_integral<_Tp>::value && !is_same<_Tp, bool>::value)
	return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)) == 0;
	#endif
	while (__count != 0) {
	if (__lhs != __rhs)
	return false;

	--__count;
	++__lhs;
	++__rhs;
	}
	return true;
	} else {
	return __builtin_memcmp(__lhs, __rhs, __count * sizeof(_Tp)) == 0;
	}
	}

	template <class _Tp, class _Up>
	_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp* __constexpr_memchr(_Tp* __str, _Up __value, size_t __count) {
	static_assert(sizeof(_Tp) == 1 && __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value,
	"Calling memchr on non-trivially equality comparable types is unsafe.");

	if (__libcpp_is_constant_evaluated()) {
	// use __builtin_char_memchr to optimize constexpr evaluation if we can
	#if _LIBCPP_STD_VER >= 17 && __has_builtin(__builtin_char_memchr)
	if constexpr (is_same_v<remove_cv_t<_Tp>, char> && is_same_v<remove_cv_t<_Up>, char>)
	return __builtin_char_memchr(__str, __value, __count);
	#endif

	for (; __count; --__count) {
	if (*__str == __value)
	return __str;
	++__str;
	}
	return nullptr;
	} else {
	char __value_buffer = 0;
	__builtin_memcpy(&__value_buffer, &__value, sizeof(char));
	return static_cast<_Tp*>(__builtin_memchr(__str, __value_buffer, __count));
	}
	}

	// This function performs an assignment to an existing, already alive TriviallyCopyable object
	// from another TriviallyCopyable object.
	//
	// It basically works around the fact that TriviallyCopyable objects are not required to be
	// syntactically copy/move constructible or copy/move assignable. Technically, only one of the
	// four operations is required to be syntactically valid -- but at least one definitely has to
	// be valid.
	//
	// This is necessary in order to implement __constexpr_memmove below in a way that mirrors as
	// closely as possible what the compiler's __builtin_memmove is able to do.
	template <class _Tp, class _Up, __enable_if_t<is_assignable<_Tp&, _Up const&>::value, int> = 0>
	_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up const& __src) {
	__dest = __src;
	return __dest;
	}

	// clang-format off
	template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value &&
	is_assignable<_Tp&, _Up&&>::value, int> = 0>
	// clang-format on
	_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up& __src) {
	__dest =
	static_cast<_Up&&>(__src); // this is safe, we're not actually moving anything since the assignment is trivial
	return __dest;
	}

	// clang-format off
	template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value &&
	!is_assignable<_Tp&, _Up&&>::value &&
	is_constructible<_Tp, _Up const&>::value, int> = 0>
	// clang-format on
	_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up const& __src) {
	// _Tp is trivially destructible, so we don't need to call its destructor to end the lifetime of the object
	// that was there previously
	std::__construct_at(std::addressof(__dest), __src);
	return __dest;
	}

	// clang-format off
	template <class _Tp, class _Up, __enable_if_t<!is_assignable<_Tp&, _Up const&>::value &&
	!is_assignable<_Tp&, _Up&&>::value &&
	!is_constructible<_Tp, _Up const&>::value &&
	is_constructible<_Tp, _Up&&>::value, int> = 0>
	// clang-format on
	_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp& __assign_trivially_copyable(_Tp& __dest, _Up& __src) {
	// _Tp is trivially destructible, so we don't need to call its destructor to end the lifetime of the object
	// that was there previously
	std::__construct_at(
	std::addressof(__dest),
	static_cast<_Up&&>(__src)); // this is safe, we're not actually moving anything since the constructor is trivial
	return __dest;
	}

	template <class _Tp, class _Up, __enable_if_t<__is_always_bitcastable<_Up, _Tp>::value, int> = 0>
	_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp*
	__constexpr_memmove(_Tp* __dest, _Up* __src, __element_count __n) {
	size_t __count = static_cast<size_t>(__n);
	if (__libcpp_is_constant_evaluated()) {
	#ifdef _LIBCPP_COMPILER_CLANG_BASED
	if (is_same<__remove_cv_t<_Tp>, __remove_cv_t<_Up> >::value) {
	::__builtin_memmove(__dest, __src, __count * sizeof(_Tp));
	return __dest;
	}
	#endif
	if (std::__is_pointer_in_range(__src, __src + __count, __dest)) {
	for (; __count > 0; --__count)
	std::__assign_trivially_copyable(__dest[__count - 1], __src[__count - 1]);
	} else {
	for (size_t __i = 0; __i != __count; ++__i)
	std::__assign_trivially_copyable(__dest[__i], __src[__i]);
	}
	} else if (__count > 0) {
	::__builtin_memmove(__dest, __src, (__count - 1) * sizeof(_Tp) + __datasizeof_v<_Tp>);
	}
	return __dest;
	}

	_LIBCPP_END_NAMESPACE_STD

	#endif // _LIBCPP___STRING_CONSTEXPR_C_FUNCTIONS_H