`<bit>` Support

#include <boost/int256/bit.hpp>

The following are functions analogous to those found in the C++20 <bit> header, but for boost::int256::uint256. None of these functions apply to signed integral types. All of them are constexpr and available using C++14 like the rest of the library, and all of them operate over the full 256 bits, so a bit set in the most significant word is 192 bits from the least significant end.

has_single_bit

Checks if x is an integral power of two. Returns true if x is a power of two; otherwise false.

namespace boost {
namespace int256 {

BOOST_INT256_HOST_DEVICE constexpr bool has_single_bit(const uint256& x) noexcept;

} // namespace int256
} // namespace boost

countl_zero

Returns the number of consecutive 0 bits in the value x, starting from the most significant. For x == 0 the result is 256, and for x == 1 it is 255.

namespace boost {
namespace int256 {

BOOST_INT256_HOST_DEVICE constexpr int countl_zero(const uint256& x) noexcept;

} // namespace int256
} // namespace boost

countl_one

Returns the number of consecutive 1 bits in the value x, starting from the most significant.

namespace boost {
namespace int256 {

BOOST_INT256_HOST_DEVICE constexpr int countl_one(const uint256& x) noexcept;

} // namespace int256
} // namespace boost

bit_width

If x is not zero, returns the number of bits needed to store the value x, which is at most 256. If x is zero, returns 0.

namespace boost {
namespace int256 {

BOOST_INT256_HOST_DEVICE constexpr int bit_width(const uint256& x) noexcept;

} // namespace int256
} // namespace boost

bit_ceil

Returns the smallest integral power of two that is not smaller than x. As for the standard function, the behavior is undefined when the result is not representable, that is when x is greater than 2²⁵⁵.

namespace boost {
namespace int256 {

BOOST_INT256_HOST_DEVICE constexpr uint256 bit_ceil(const uint256& x) noexcept;

} // namespace int256
} // namespace boost

bit_floor

Returns the largest integral power of two that is not greater than x. If x is 0 then returns 0.

namespace boost {
namespace int256 {

BOOST_INT256_HOST_DEVICE constexpr uint256 bit_floor(const uint256& x) noexcept;

} // namespace int256
} // namespace boost

countr_zero

Returns the number of consecutive 0 bits in the value x, starting from the least significant. For x == 0 the result is 256.

namespace boost {
namespace int256 {

BOOST_INT256_HOST_DEVICE constexpr int countr_zero(const uint256& x) noexcept;

} // namespace int256
} // namespace boost

countr_one

Returns the number of consecutive 1 bits in the value x, starting from the least significant.

namespace boost {
namespace int256 {

BOOST_INT256_HOST_DEVICE constexpr int countr_one(const uint256& x) noexcept;

} // namespace int256
} // namespace boost

rotl

Computes the result of bitwise left-rotating the value of x by s positions. This operation is also known as a left circular shift. The count is taken modulo 256, and a negative count rotates in the other direction, so rotl(x, 256) == x and rotl(x, -1) == rotr(x, 1).

namespace boost {
namespace int256 {

BOOST_INT256_HOST_DEVICE constexpr uint256 rotl(const uint256& x, int s) noexcept;

} // namespace int256
} // namespace boost

rotr

Computes the result of bitwise right-rotating the value of x by s positions. This operation is also known as a right circular shift. The count is handled as for rotl.

namespace boost {
namespace int256 {

BOOST_INT256_HOST_DEVICE constexpr uint256 rotr(const uint256& x, int s) noexcept;

} // namespace int256
} // namespace boost

popcount

Returns the number of 1 bits in x, which is at most 256.

namespace boost {
namespace int256 {

BOOST_INT256_HOST_DEVICE constexpr int popcount(const uint256& x) noexcept;

} // namespace int256
} // namespace boost

byteswap

Reverses the 32 bytes of the given value x, so the words swap places and each one is individually byte reversed. Unlike the byte order conversions, this is a pure value transformation and does not depend on the host byte order.

namespace boost {
namespace int256 {

BOOST_INT256_HOST_DEVICE constexpr uint256 byteswap(const uint256& x) noexcept;

} // namespace int256
} // namespace boost

See the bit manipulation example for a program that exercises all of these.

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<bit> Support