std::bit_expand - cppreference.com
From cppreference.com
| Defined in header |
||
template< class T > constexpr int bit_expand( T x, T m ) noexcept; |
(since C++29) | |
Selects the least significant bits of x and places them where m has a 1-bit. The remaining bits are 0.
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).
Parameters
| x | - | value of unsigned integer type |
| m | - | value of unsigned integer type |
Return value
x with the bit deposit through the mask m applied.
Notes
The function is has the same result as the PDEP x86_64 and PDEP ARM instructions.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_bitops |
202606L |
(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_compress(T x) noexcept { T result = 0; for (int i = 0, j = 0; i < numeric_limits<T>::digits; ++i) { bool mask_bit = (m >> i) & 1; result |= (mask_bit & (x >> j)) << i; j += mask_bit; } return result; }
Example
#include <bit> #include <cstdint> static_assert( std::bit_expand( std::uint16_t{0xABCD}, // source std::uint16_t{0x0F0F}) // mask == std::uint16_t{0x0C0D} // result ); static_assert( std::bit_expand( std::uint8_t{0b1010'1001}, // source std::uint8_t{0b0011'0011}) // mask == std::uint8_t{0b0010'0001} // result ); int main() {}
See also
compresses bits of an operand using a mask (PEXT) (function template) [edit] |