Stackoverflow relevant comment: https://stackoverflow.com/questions/180947/base64-decode-snippet-in-c#comment137345692_13935718

Claude version:

std::string base64encode(const char* data, size_t length) { static const char* base64_chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" "abcdefghijklmnopqrstuvwxyz" "0123456789+/";

  std::string result;
  result.reserve(((length + 2) / 3) * 4);

  size_t i = 0;
  unsigned char char_array_3[3];
  unsigned char char_array_4[4];

  while (length--)
  {
    char_array_3[i++] = *(data++);
    if (i == 3)
    {
      char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
      char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);
      char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);
      char_array_4[3] = char_array_3[2] & 0x3f;

      for (i = 0; i < 4; i++)
        result += base64_chars[char_array_4[i]];
      i = 0;
    }
  }

  if (i)
  {
    for (size_t j = i; j < 3; j++)
      char_array_3[j] = '\0';

    char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
    char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);
    char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);

    for (size_t j = 0; j < i + 1; j++)
      result += base64_chars[char_array_4[j]];

    while (i++ < 3)
      result += '=';
  }

  return result;
}