Function decode_base64

src/gpu/cl/ClKernelLibrary.cpp:58–118

Decode a base64 encoded string * * @param[in] str Base64 encoded string to decode * * @return The decode string in case of a valid, non-empty string otherwise an empty string */

 * @return The decode string in case of a valid, non-empty string otherwise an empty string
 */
std::string decode_base64(const std::string &str)
{
    constexpr const char pad_char = '=';

    // Handle empty string
    if (str.empty())
    {
        return {};
    }

    // Base64 encoded string has size multiple of 4
    if (str.length() % 4)
    {
        return {};
    }

    //
    // Check encoded string padding
    std::size_t padding = (str.rbegin()[0] == pad_char) + (str.rbegin()[1] == pad_char);
    const int   str_len = str.size();

    // Reserve memory for the decoded string
    // Note each 4 consecutive elements of 6-bit encode 3 bytes
    std::string dec_b64;
    dec_b64.reserve(((str_len / 4) * 3));

    // Block decoding function (exclude padding)
    int       c   = 0;
    const int end = str_len - 4 - padding;
    for (; c <= end; c += 4)
    {
        const int byte0 = b64_invtab[str[c]];
        const int byte1 = b64_invtab[str[c + 1]];
        const int byte2 = b64_invtab[str[c + 2]];
        const int byte3 = b64_invtab[str[c + 3]];

        dec_b64.push_back((byte0 << 2) | (byte1 >> 4));
        dec_b64.push_back((byte1 << 4) | (byte2 >> 2));
        dec_b64.push_back((byte2 << 6) | (byte3));
    }

    // Last step that might contain padding symbols
    if (padding == 1)
    {
        const int byte0 = b64_invtab[str[c]];
        const int byte1 = b64_invtab[str[c + 1]];
        const int byte2 = b64_invtab[str[c + 2]];

        dec_b64.push_back((byte0 << 2) | (byte1 >> 4));
        dec_b64.push_back((byte1 << 4) | (byte2 >> 2));
    }
    else if (padding == 2)
    {
        const int byte0 = b64_invtab[str[c]];
        const int byte1 = b64_invtab[str[c + 1]];

        dec_b64.push_back((byte0 << 2) | (byte1 >> 4));
    }