std::bit_floor
From cppreference.com
C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Utilities library
Relational operators (deprecated in C++20) Integer comparison functions
Swap and type operations Common vocabulary types
Type support (basic types, RTTI)
Library feature-test macros (C++20)
(C++11)
(C++20)
(C++26)
(C++20)
Coroutine support (C++20)
Contract support (C++26)
(C++20)(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)(C++20)(C++20)
(C++20)(C++20)(C++20)
General utilities
(C++20)(C++20)(C++20)
(C++20)(C++20)(C++20)
(C++20)
Bit manipulation
(C++20)
(C++23)
(C++20)
(C++20)
bit_floor
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
Defined in header
<bit>
template< class T >
constexpr T bit_floor( T x ) noexcept;
(since C++20)
constexpr T bit_floor( T x ) noexcept;
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).
[edit] Parameters
x
-
unsigned integer value
[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.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_int_pow2 |
202002L |
(C++20) | Integral power-of-2 operations |
[edit] Possible implementation
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_floor(T x) noexcept { if (x != 0) return T{1} << (std::bit_width (x) - 1); return 0; }
[edit] Example
Run this code
#include <bit> #include <bitset> #include <iostream> 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
(C++20)
(function template) [edit]
(C++20)
(function template) [edit]