std::bit_width

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Defined in header`<bit>`
template<class T> constexprint bit_width( T x)noexcept;		(since C++20)

Ifx is not zero, calculates the number of bits needed to store the valuex, that is,\(1 + \lfloor \log_2(x) \rfloor\)1 + floor(log2(x)). Ifx is zero, returns zero.

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).

[edit]Parameters

unsigned integer value

[edit]Return value

Zero ifx is zero; otherwise, one plus the base-2 logarithm ofx, with any fractional part discarded.

[edit]Notes

This function is equivalent toreturnstd::numeric_limits<T>::digits-std::countl_zero(x);.

Feature-test macro	Value	Std	Feature
`__cpp_lib_int_pow2`	`202002L`	(C++20)	Integral power-of-2 operations

[edit]Example

Run this code

#include <bit>#include <bitset>#include <iostream> int main(){for(unsigned x{}; x!=010;++x)std::cout<<"bit_width( "<<std::bitset<4>{x}<<" ) = "<< std::bit_width(x)<<'\n';}

Output:

bit_width( 0000 ) = 0bit_width( 0001 ) = 1bit_width( 0010 ) = 2bit_width( 0011 ) = 2bit_width( 0100 ) = 3bit_width( 0101 ) = 3bit_width( 0110 ) = 3bit_width( 0111 ) = 3