std::bit_repeat - cppreference.com
Namespaces
Variants

    std::bit_repeat

    From cppreference.com
     
    C++
     
    Utilities library
    General utilities
    Relational operators (deprecated in C++20)
    Integer comparison functions
    (C++20)(C++20)(C++20)    
    (C++20)
    Swap and type operations
    (C++20)
    (C++14)
    (C++11)
    (C++23)
    (C++11)
    (C++23)
    (C++11)
    (C++11)
    (C++17)
    Common vocabulary types
    (C++11)
    (C++17)
    (C++17)
    (C++17)
    (C++11)
    (C++11)
    (C++17)
    (C++17)
    (C++23)



     
    Bit manipulation
    (C++20)
    (C++23)
    Integral powers of 2
    (C++20)
    (C++20)
    (C++20)
    (C++20)
    Shifting
    (C++29)
    (C++29)
    Rotating
    (C++20)
    (C++20)
    Counting
    (C++20)
    (C++20)
    (C++20)
    (C++20)
    (C++20)
    Permutation
    (C++29)
    (C++29)
    (C++29)
    (C++29)
    Endian
    (C++20)
     
    Defined in header <bit> 
    template< class T >
constexpr T bit_repeat( T pattern, int length );
    		(since C++29)

    Repeats the bit pattern in pattern of length length as many times as fits into the result (with the last repetition potentially truncated).

    If length is less than or equal to 0, the behavior is undefined. Call to this function is permitted in constant evaluation only if the undefined behavior does not occur.

    Parameters

    pattern - the bit pattern to repeat
    length - the length of the bit pattern
    Type requirements
    T - must be an unsigned integer type (that is, unsigned char, unsigned short, unsigned int, unsigned long, unsigned long long, or an extended unsigned integer type) in order to participate in overload resolution.

    Return value

    The repeated bit pattern.

    Exceptions

    Throws nothing.

    Notes

    Feature-test macro Value Std Feature
    __cpp_lib_bitops 202607L (C++29) Bit permutations

    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_repeat(T pattern, int length) noexcept
{
    T result = 0;
    for (int i = 0; i != std::numeric_limits<T>::digits; ++i)
        result |= ((pattern >> (i % length)) & 1) << i;
    return result;
}

    Example

    Run this code
    #include <bit>
#include <cstdint>

static_assert(
    std::bit_repeat(
        std::uint8_t{1}, 1) ==
        std::uint8_t{0b1111'1111} and
    std::bit_repeat(
        std::uint8_t{0b1110}, 2) ==
        std::uint8_t{0b1010'1010} and
    std::bit_repeat(
        std::uint8_t{0b101}, 3) ==
        std::uint8_t{0b1'101'101} and
    std::bit_repeat(
        std::uint16_t{0b1100}, 4) ==
        std::uint16_t{0b1100'1100'1100'1100}
);

int main() {}

    See also