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| Integral powers of2 | ||||
has_single_bit (C++20) | ||||
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Defined in header <bit> | ||
template<class T> constexprbool has_single_bit( T x)noexcept; | (since C++20) | |
Checks ifx is an integral power of two.
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 |
true ifx is an integral power of two; otherwisefalse.
Prior toP1956R1, the proposed name for this function template wasispow2.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_int_pow2 | 202002L | (C++20) | Integral power-of-2 operations |
template<typename T,typename ...U>concept neither=(!std::same_as<T, U>&& ...); template<typename T>concept strict_unsigned_integral=std::unsigned_integral<T>&& neither<T,bool,char, char8_t,char16_t,char32_t,wchar_t>; // First versionconstexprbool has_single_bit(strict_unsigned_integralauto x)noexcept{return x&&!(x&(x-1));} // Second versionconstexprbool has_single_bit(strict_unsigned_integralauto x)noexcept{returnstd::popcount(x)==1;} |
#include <bit>#include <bitset>#include <cmath>#include <iostream> int main(){for(auto u{0u}; u!=0B1010;++u){std::cout<<"u = "<< u<<" = "<<std::bitset<4>(u);if(std::has_single_bit(u))std::cout<<" = 2^"<<std::log2(u)<<" (is power of two)";std::cout<<'\n';}}
Output:
u = 0 = 0000u = 1 = 0001 = 2^0 (is power of two)u = 2 = 0010 = 2^1 (is power of two)u = 3 = 0011u = 4 = 0100 = 2^2 (is power of two)u = 5 = 0101u = 6 = 0110u = 7 = 0111u = 8 = 1000 = 2^3 (is power of two)u = 9 = 1001
(C++20) | counts the number of1 bits in an unsigned integer (function template)[edit] |
| returns the number of bits set totrue (public member function of std::bitset<N>)[edit] | |
| accesses specific bit (public member function of std::bitset<N>)[edit] |
