Bits.h

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//   Copyright 2024 Jaroslav Pevno, JPLSpatial is offered under the terms of the ISC license:
//
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#pragma once
 
#include <algorithm>
#include <concepts>
#include <bit>
#include <limits>
#include <climits>
 
namespace JPL
{
    template<std::integral T>
    [[nodiscard]] constexpr T Byteswap(T value) noexcept
    {
#if defined(__cpp_lib_byteswap) && __cpp_lib_byteswap >= 202110L
        return std::byteswap(value);
#else
        static_assert(std::has_unique_object_representations_v<T>, "T may not have padding bits");
        auto value_representation = std::bit_cast<std::array<std::byte, sizeof(T)>>(value);
        std::ranges::reverse(value_representation);
        return std::bit_cast<T>(value_representation);
#endif
    }
 
    template <class T> requires (std::unsigned_integral<T>)
    [[nodiscard]] constexpr int MSBIndex(T n) noexcept
    {
        if (n == T(0))
            return -1;
        return std::numeric_limits<T>::digits - std::countl_zero(n) - 1;
    }
 
    template<std::integral T>
    [[nodiscard]] constexpr T RoundUpBy4(T n) noexcept
    {
        return (n + T(3)) & ~T(3);
    }
 
    template<std::integral T>
    [[nodiscard]] constexpr std::size_t BitWidthOf() noexcept { return sizeof(T) * CHAR_BIT; }
 
} // namespace JPL