urlencode & urldecode

//not by me

unsigned char to_hex( unsigned char x )
{
    return x + (x > 9 ? ('A'-10) : '0');
}

const std::string urlencode( const std::string& s )
{
    std::ostringstream os;

    for ( std::string::const_iterator ci = s.begin(); ci != s.end(); ++ci )
    {
        if ( (*ci >= 'a' && *ci <= 'z') ||
                (*ci >= 'A' && *ci <= 'Z') ||
                (*ci >= '0' && *ci <= '9') )
        { // allowed
            os << *ci;
        }
        else if ( *ci == ' ')
        {
            os << '+';
        }
        else
        {
            os << '%' << to_hex(*ci >> 4) << to_hex(*ci % 16);
        }
    }

    return os.str();
}

unsigned char from_hex (
    unsigned char ch
)
{
    if (ch <= '9' && ch >= '0')
        ch -= '0';
    else if (ch <= 'f' && ch >= 'a')
        ch -= 'a' - 10;
    else if (ch <= 'F' && ch >= 'A')
        ch -= 'A' - 10;
    else
        ch = 0;
    return ch;
}

const std::string urldecode (
    const std::string& str
)
{
    using namespace std;
    string result;
    string::size_type i;
    for (i = 0; i < str.size(); ++i)
    {
        if (str[i] == '+')
        {
            result += ' ';
        }
        else if (str[i] == '%' && str.size() > i+2)
        {
            const unsigned char ch1 = from_hex(str[i+1]);
            const unsigned char ch2 = from_hex(str[i+2]);
            const unsigned char ch = (ch1 << 4) | ch2;
            result += ch;
            i += 2;
        }
        else
        {
            result += str[i];
        }
    }
    return result;
}