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std::bit_width(3)	       C++ Standard Libary	       std::bit_width(3)

NAME
     std::bit_width - std::bit_width

Synopsis
	Defined in header <bit>
	template< class T >			  (since C++20)
	constexpr int bit_width( T x ) noexcept;

	If  x  is  not	zero,  calculates the number of bits needed to store the
     value x, that
	is, \(1 + \lfloor \log_2(x) \rfloor\)1 + floor(log
	2(x)). If x is zero, returns zero.

	This overload participates in overload resolution only if T  is  an  un-
     signed integer
	type  (that  is,  unsigned  char, unsigned short, unsigned int, unsigned
     long, unsigned
	long long, or an extended unsigned integer type).

Parameters
	x - unsigned integer value

Return value
	Zero if x is zero; otherwise, one plus the base-2 logarithm of	x,  with
     any
	fractional part discarded.

Notes
	This function is equivalent to return std::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

Example
     // Run this code

      #include <bit>
      #include <bitset>
      #include <iostream>

      int main()
      {
	  for (unsigned x{0}; x != 8; ++x)
	  {
	      std::cout
		  << "bit_width( "
		  << std::bitset<4>{x} << " ) = "
		  << std::bit_width(x) << '\n';
	  }
      }

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

	Defect reports

	The  following	behavior-changing  defect  reports were applied retroac-
     tively to
	previously published C++ standards.

	   DR	 Applied to		 Behavior as published		    Cor-
     rect behavior
	LWG 3656 C++20	    the return type of bit_width is the same as the made
     it int
			    type of its function argument

See also
	countl_zero counts the number of consecutive 0 bits, starting  from  the
     most
	(C++20)     significant bit
		    (function template)

http://cppreference.com 	   2024.06.10		       std::bit_width(3)
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