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| Integral powers of2 | ||||
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bit_ceil (C++20) | ||||
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Defined in header <bit> | ||
template<class T> constexpr T bit_ceil( T x); | (since C++20) | |
Calculates the smallest integral power of two that is not smaller thanx.
If that value is not representable inT, the behavior is undefined. Call to this function is permitted inconstant evaluation only if the undefined behavior does not occur.
This overload participates in overload resolution only ifT is an unsigned integer type (that is,unsignedchar,unsignedshort,unsignedint,unsignedlong,unsignedlonglong, or an extended unsigned integer type).
Contents |
| x | - | value of unsigned integer type |
The smallest integral power of two that is not smaller thanx.
Throws nothing.
Prior toP1956R1, the proposed name for this function template wasceil2.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_int_pow2 | 202002L | (C++20) | Integral power-of-2 operations |
See possible implementations inlibstdc++ (gcc) andlibc++ (clang).
template<typename T,typename ...U>concept neither=(!std::same_as<T, U>&& ...); template<std::unsigned_integral T> requires neither<T,bool,char, char8_t,char16_t,char32_t,wchar_t>constexpr T bit_ceil(T x)noexcept{if(x<= 1u)return T(1);ifconstexpr(std::same_as<T, decltype(+x)>)return T(1)<<std::bit_width(T(x-1));else{// for types subject to integral promotionconstexprint offset_for_ub=std::numeric_limits<unsigned>::digits-std::numeric_limits<T>::digits;return T(1u<<(std::bit_width(T(x-1))+ offset_for_ub)>> offset_for_ub);}} |
#include <bit>#include <bitset>#include <iostream> int main(){using bin=std::bitset<8>;for(auto x{0U};0XA!= x;++x)std::cout<<"bit_ceil( "<< bin(x)<<" ) = "<< bin(std::bit_ceil(x))<<'\n';}
Output:
bit_ceil( 00000000 ) = 00000001bit_ceil( 00000001 ) = 00000001bit_ceil( 00000010 ) = 00000010bit_ceil( 00000011 ) = 00000100bit_ceil( 00000100 ) = 00000100bit_ceil( 00000101 ) = 00001000bit_ceil( 00000110 ) = 00001000bit_ceil( 00000111 ) = 00001000bit_ceil( 00001000 ) = 00001000bit_ceil( 00001001 ) = 00010000
(C++20) | finds the largest integral power of2 not greater than the given value (function template)[edit] |
