byteswap.h

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// This file's extension implies that it's C, but it's really -*- C++ -*-.
/*
 * Copyright (C) 2002-2025 CERN for the benefit of the ATLAS collaboration.
 */
 
 
#ifndef CXXUTILS_BYTESWAP_H
#define CXXUTILS_BYTESWAP_H
 
 
#include <version>
#include <concepts>
#include <bit>
#include <array>
#include <algorithm>
 
 
namespace CxxUtils {
 
 
#if __cpp_lib_byteswap
 
// Use library version if available.
using std::byteswap;
 
#else
 

template<std::integral T>
constexpr T byteswap(T value) noexcept
{
    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 // not __cpp_lib_byteswap
 
 
} // namespace CxxUtils
 
 
#endif // not CXXUTILS_BYTESWAP_H