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std::bit_ceil(3) C++ Standard Libary std::bit_ceil(3) NAME std::bit_ceil - std::bit_ceil Synopsis Defined in header <bit> template< class T > (since C++20) constexpr T bit_ceil( T x ); Calculates the smallest integral power of two that is not smaller than x. If that value is not representable in T, the behavior is undefined. Call to this function is permitted in constant evaluation only if the undefined behavior does not occur. This overload participates in overload resolution only if T is an unsigned integer type (that is, unsigned char, unsigned short, unsigned int, unsigned long, unsigned long long, or an extended unsigned integer type). Parameters x - value of unsigned integer type Return value The smallest integral power of two that is not smaller than x. Exceptions Throws nothing. Notes Feature-test macro: __cpp_lib_int_pow2 Possible implementation See possible implementations in libstdc++ (gcc) and libc++ (clang) template <std::unsigned_integral T> requires !std::same_as<T, bool> && !std::same_as<T, char> && !std::same_as<T, char8_t> && !std::same_as<T, char16_t> && !std::same_as<T, char32_t> && !std::same_as<T, wchar_t> constexpr T bit_ceil(T x) noexcept { if (x <= 1u) return T(1); if constexpr (std::same_as<T, decltype(+x)>) return T(1) << std::bit_width(T(x - 1)); else { // for types subject to integral promotion constexpr int offset_for_ub = std::numeric_limits<unsigned>::digits - std::nu- meric_limits<T>::digits; return T(1u << (std::bit_width(T(x - 1)) + offset_for_ub) >> offset_for_ub); } } Example // Run this code #include <bit> #include <bitset> #include <iostream> auto main() -> signed int // :() { using bin = std::bitset<8>; for (unsigned x{0}; x != 10; ++x) { unsigned const z = std::bit_ceil(x); // `ceil2` before P1956R1 std::cout << "bit_ceil( " << bin(x) << " ) = " << bin(z) << '\n'; } } Output: bit_ceil( 00000000 ) = 00000001 bit_ceil( 00000001 ) = 00000001 bit_ceil( 00000010 ) = 00000010 bit_ceil( 00000011 ) = 00000100 bit_ceil( 00000100 ) = 00000100 bit_ceil( 00000101 ) = 00001000 bit_ceil( 00000110 ) = 00001000 bit_ceil( 00000111 ) = 00001000 bit_ceil( 00001000 ) = 00001000 bit_ceil( 00001001 ) = 00010000 See also bit_floor finds the largest integral power of two not greater than the given value (C++20) (function template) http://cppreference.com 2022.07.31 std::bit_ceil(3)
NAME | Synopsis | Parameters | Return value | Exceptions | Notes | Possible implementation | Example | Output: | See also
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