to_little_endian.hpp

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// SPDX-FileCopyrightText: 2006-2025 Knut Reinert & Freie Universität Berlin
// SPDX-FileCopyrightText: 2016-2025 Knut Reinert & MPI für molekulare Genetik
// SPDX-License-Identifier: BSD-3-Clause

 
#pragma once
 
#include <bit>
#include <concepts>
 
// Find correct header for byte-order conversion functions.
#if __has_include(<endian.h>) // unix GLIBC
#    include <endian.h>
#elif __has_include(<sys/endian.h>) // *BSD
#    include <sys/endian.h>
#endif // __has_include(endian.h)
 
#include <seqan3/core/platform.hpp>
 
namespace seqan3::detail
{
template <std::integral type>
constexpr type to_little_endian(type const in) noexcept
{
    if constexpr (std::endian::native == std::endian::little)
    {
        return in;
    }
    else if constexpr (std::endian::native == std::endian::big)
    {
        static_assert(sizeof(type) <= 8,
                      "Can only convert the byte encoding for integral numbers with a size of up to 8 bytes.");
        static_assert(std::has_single_bit(sizeof(type)),
                      "Can only convert the byte encoding for integral numbers whose byte size is a power of two.");
 
        if constexpr (sizeof(type) == 2)
            return htole16(in);
        else if constexpr (sizeof(type) == 4)
            return htole32(in);
        else if constexpr (sizeof(type) == 8)
            return htole64(in);
        else
            return in; // single byte.
    }
    else
    {
        static_assert(std::endian::native == std::endian::little || std::endian::native == std::endian::big,
                      "Expected a little-endian or big-endian platform.");
    }
}
 
} // namespace seqan3::detail