midpoint.h

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#pragma once
 
#include "di/function/curry_back.h"
#include "di/meta/language.h"
#include "di/types/prelude.h"
 
namespace di::math {
namespace detail {
    struct MidpointFunction {
        template<concepts::Integral T>
        requires(!concepts::SameAs<T, bool>)
        constexpr auto operator()(T a, T b) const -> T {
            // Compute the midpoint without signed overflow.
            // The implementation is from this CppCon talk:
            // https://m.youtube.com/watch?v=sBtAGxBh-XI
            using U = meta::MakeUnsigned<T>;
            int sign = 1;
            U min = a;
            U max = b;
            if (b < a) {
                sign = -1;
                min = b;
                max = a;
            }
            return a + sign * T(U(max - min) >> 1);
        }
 
        template<concepts::Pointer T>
        requires(concepts::Object<meta::RemovePointer<T>>)
        constexpr auto operator()(T a, T b) const -> T {
            return a + (b - a) / 2;
        }
    };
}
 
constexpr inline auto midpoint = function::curry_back(detail::MidpointFunction {}, meta::c_<2ZU>);
}
 
namespace di {
using math::midpoint;
}