cpplib/include/cpp/lib_bit at master · vslavski/cpplib · GitHub

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/* File: /cpp/lib_bit
 *
 * This file is a part of cpplib project which is distributed under MIT License.
 * See file LICENSE for full license details.
 *
 * Copyright (c) 2020-present Nikita Zuev (V.Slavski!) <[email protected]>
 */
#ifndef CPPLIB__cpp__lib_bit
#define CPPLIB__cpp__lib_bit

#include <bit>

/////////////////////////////////// bit_cast /////////////////////////////////////////////

#ifdef __cpp_lib_bit_cast

namespace cpp {
template <class To, class From>
requires ( false/*Consider use `std::bit_cast`*/ )
inline constexpr To bit_cast( const From & from ) noexcept { return ::std::bit_cast<To>( from ); }
} // namespace cpp

#else

#pragma message("__cpp_lib_bit_cast feature unavailable, consider use `cpp::bit_cast`")

#include <cstring>

#include <type_traits>

namespace cpp {

/** @copyright As the original source code was taken from [cppreference.com](https://cppreference.com/) site, source
 *  code of this function is distributed under [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0/) license.
 *  @see https://en.cppreference.com/w/cpp/numeric/bit_cast
 */

template <class To, class From>
// constexpr support needs compiler magic
inline To bit_cast( const From & src ) noexcept {
	static_assert( sizeof(To) == sizeof(From) );
	// this implementation requires that To is trivially default constructible
	static_assert( ::std::is_trivially_copyable_v<From> );
	static_assert( ::std::is_trivial_v<To> );
	To dst;
	::std::memcpy( &dst, &src, sizeof(To) );
	return dst;
}

} // namespace cpp

#endif // __cpp_lib_bit_cast

/////////////////////////////////// byteswap /////////////////////////////////////////////

#ifdef __cpp_lib_byteswap

#pragma message("__cpp_lib_byteswap feature support found")
namespace cpp {
template <class T>
inline constexpr T byteswap( T x ) noexcept { return ::std::byteswap( x ); }
} // namespace cpp

#else

#include <cstdint>

namespace cpp {

inline constexpr ::std::uint16_t byteswap( ::std::uint16_t v ) noexcept {
	return ( v << 8U ) | ( v >> 8U );
}

inline constexpr ::std::uint32_t byteswap( ::std::uint32_t v ) noexcept {
	return
		( (::std::uint32_t)byteswap((::std::uint16_t)( v & 0xFFFFU )) << 16U )
		|
		( (::std::uint32_t)byteswap((::std::uint16_t)( v >> 16U )) );
}

inline constexpr uint64_t byteswap( ::std::uint64_t v ) noexcept {
	return
		( (::std::uint64_t)byteswap((::std::uint32_t)( v & 0xFFFFFFFFUL )) << 32U )
		|
		( (::std::uint64_t)byteswap((::std::uint32_t)( v >> 32U )) );
}

} // namespace cpp

#endif // __cpp_lib_byteswap

//////////////// has_single_bit, bit_ceil, bit_floor, bit_width //////////////////////////

#ifdef __cpp_lib_int_pow2

namespace cpp {
template <class T> requires ( false/*Consider use `std::has_single_bit`*/ )
inline constexpr bool has_single_bit( T x ) noexcept { return ::std::has_single_bit( x ); }
template <class T> requires ( false/*Consider use `std::bit_ceil`*/ )
inline constexpr T bit_ceil( T x ) noexcept { return ::std::bit_ceil( x ); }
template <class T> requires ( false/*Consider use `std::bit_floor`*/ )
inline constexpr T bit_floor( T x ) noexcept { return ::std::bit_floor( x ); }
template <class T> requires ( false/*Consider use `std::bit_width`*/ )
inline constexpr T bit_width( T x ) noexcept { return ::std::bit_width( x ); }
} // namespace cpp

#else

#pragma message("__cpp_lib_int_pow2 feature unavailable, consider use `cpp::has_single_bit` \
, `cpp::bit_ceil`, `cpp::bit_floor`, `cpp::bit_width`")

#include <limits>
#include <type_traits>

namespace cpp {

/** @copyright As the original source code was taken from [cppreference.com](https://cppreference.com/) site, source
 *  code of this function is distributed under [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0/) license.
 *  @see https://en.cppreference.com/w/cpp/numeric/has_single_bit
 */

template <class T>
inline constexpr bool has_single_bit( T x ) noexcept {
	return ::std::popcount( x ) == 1;
}

/** @copyright As the original source code was taken from [cppreference.com](https://cppreference.com/) site, source
 *  code of this function is distributed under [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0/) license.
 *  @see https://en.cppreference.com/w/cpp/numeric/bit_width
 */

template <class T>
inline constexpr T bit_width( T x ) noexcept {
	return ::std::numeric_limits<T>::digits - ::std::countl_zero( x );
}

/** @copyright As the original source code was taken from [cppreference.com](https://cppreference.com/) site, source
 *  code of this function is distributed under [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0/) license.
 *  @see https://en.cppreference.com/w/cpp/numeric/bit_ceil
 */

template <class T>
inline constexpr T bit_ceil( T x ) noexcept {
	if ( x <= 1U )
		return T{ 1 };
	if constexpr ( ::std::is_same_v< T, decltype(+x) > )
		return T{ 1 } << ::cpp::bit_width( T{ x - 1 } );
	else {
		constexpr auto offset_for_ub
			= ::std::numeric_limits<unsigned>::digits - ::std::numeric_limits<T>::digits;
		return T{ 1U << ( ::cpp::bit_width( T{ x - 1 } ) + offset_for_ub ) >> offset_for_ub };
	}
}

/** @copyright As the original source code was taken from [cppreference.com](https://cppreference.com/) site, source
 *  code of this function is distributed under [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0/) license.
 *  @see https://en.cppreference.com/w/cpp/numeric/bit_floor
 */

template <class T>
inline constexpr T bit_floor( T x ) noexcept {
	if ( x == 0 )
		return 0;
	return T{ 1 } << ( ::cpp::bit_width( x ) - 1 );
}

} // namespace cpp

#endif // __cpp_lib_int_pow2

///////////////////////// (from|to)_(little|big)_endian //////////////////////////////////

namespace cpp {

template< class T >
inline constexpr T from_little_endian( T v ) noexcept {
	return ::std::endian::native == ::std::endian::little
		? v : byteswap( v );
}

template< class T >
inline constexpr T to_little_endian( T v ) noexcept {
	return from_little_endian( v );
}

template< class T >
inline constexpr T from_big_endian( T v ) noexcept {
	return ::std::endian::native == ::std::endian::big
		? v : byteswap( v );
}

template< class T >
inline constexpr T to_big_endian( T v ) noexcept {
	return from_big_endian( v );
}

} // namespace cpp

#endif // CPPLIB__cpp__lib_bit