bit_ceil.h

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#pragma once
 
#include "di/bit/operation/bit_width.h"
#include "di/meta/core.h"
 
namespace di::bit {
namespace detail {
    struct BitCeilFunction {
        template<concepts::UnsignedInteger T>
        constexpr auto operator()(T value) const -> T {
            if (value <= 1U) {
                return T(1);
            }
            if constexpr (concepts::SameAs<T, decltype(+value)>) {
                return T(1) << bit_width(T(value - 1));
            } else {
                // Ensure UB if the result cannot fit inside T. This is needed because
                // T promotes to an int automatically.
                constexpr int extra_offset = math::NumericLimits<unsigned int>::digits - math::NumericLimits<T>::digits;
                return T(1U << (bit_width(T(value - 1)) + extra_offset) >> extra_offset);
            }
        }
    };
}
 
constexpr inline auto bit_ceil = detail::BitCeilFunction {};
}
 
namespace di {
using bit::bit_ceil;
}