Function encode

src/base64.cpp:42–71

base64 encoder snippet altered from https://stackoverflow.com/a/37109258

/// base64 encoder snippet altered from https://stackoverflow.com/a/37109258
std::string encode(const std::vector<byte>& buf)
{
    std::size_t len = buf.size();
    std::vector<byte> res_vec((len + 2) / 3 * 4, '=');
    std::size_t j         = 0;
    std::size_t remaining = len % 3;
    const size_t last     = len - remaining;

    for(size_t i = 0; i < last; i += 3)
    {
        std::size_t n = static_cast<std::size_t>(buf.at(i)) << 16u |
                        static_cast<std::size_t>(buf.at(i + 1)) << 8u |
                        static_cast<std::size_t>(buf.at(i + 2));
        res_vec.at(j++) = b64_chars.at(n >> 18u);
        res_vec.at(j++) = b64_chars.at(n >> 12u & 0x3Fu);
        res_vec.at(j++) = b64_chars.at(n >> 6u & 0x3Fu);
        res_vec.at(j++) = b64_chars.at(n & 0x3Fu);
    }
    // Set padding
    if(remaining != 0)
    {
        std::size_t n   = --remaining == 0 ? static_cast<std::size_t>(buf.at(last))
                                           : static_cast<std::size_t>(buf.at(last)) << 8u |
                                               static_cast<std::size_t>(buf.at(last + 1));
        res_vec.at(j++) = b64_chars.at(remaining == 0 ? n >> 2u : n >> 10u & 0x3Fu);
        res_vec.at(j++) = b64_chars.at(remaining == 0 ? n << 4u & 0x3Fu : n >> 4u & 0x03Fu);
        res_vec.at(j++) = remaining == 0 ? '=' : b64_chars.at(n << 2u & 0x3Fu);
    }
    return {res_vec.begin(), res_vec.end()};
}

} // namespace