std::bit_floor - cppreference.com (original) (raw)

| Defined in header | | | | ------------------------------------------------------------- | | ------------- | | template< class T > constexpr T bit_floor( T x ) noexcept; | | (since C++20) |

If x is not zero, calculates the largest integral power of two that is not greater than x. If x is zero, returns zero.

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).

Contents

• 1 Parameters
• 2 Return value
• 3 Notes
• 4 Possible implementation
• 5 Example
• 6 See also

[edit] Parameters

[edit] Return value

Zero if x is zero; otherwise, the largest integral power of two that is not greater than x.

[edit] Notes

Prior to P1956R1, the proposed name for this function template was floor2.

[edit] Possible implementation

template<typename T, typename ... U> concept neither = (<T, U> && ...);   template<std::unsigned_integral T> requires neither<T, bool, char, char8_t, char16_t, char32_t, wchar_t> constexpr T bit_floor(T x) noexcept { if (x != 0) return T{1} << (std::bit_width(x) - 1); return 0; }

[edit] Example

#include #include #include   int main() { using bin = std::bitset<8>; for (unsigned x{}; x != 012; ++x) std::cout << "bit_floor( " << bin(x) << " ) = " << bin(std::bit_floor(x)) << '\n'; }

Output:

bit_floor( 00000000 ) = 00000000 bit_floor( 00000001 ) = 00000001 bit_floor( 00000010 ) = 00000010 bit_floor( 00000011 ) = 00000010 bit_floor( 00000100 ) = 00000100 bit_floor( 00000101 ) = 00000100 bit_floor( 00000110 ) = 00000100 bit_floor( 00000111 ) = 00000100 bit_floor( 00001000 ) = 00001000 bit_floor( 00001001 ) = 00001000

[edit] See also

| | finds the smallest integral power of 2 not less than the given value (function template) [edit] | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | computes the result of bitwise right-rotation (function template) [edit] | | | finds the smallest number of bits needed to represent the given value (function template) [edit] | | | checks if a number is an integral power of 2 (function template) [edit] |