ipv6.cc

#include <string>

int base16Pows[] = {
    0x1,
    0x10,
    0x100,
    0x1000,
    0x10000
};

inline int convertFromHex(char hex, int position)
{
    int offset;
    if (hex >= '0' && hex <= '9') {
        offset = '0';
    } else if (hex >= 'a' && hex <= 'f') {
        offset = 'a' - 10;
    } else if (hex >= 'A' && hex <= 'F') {
        offset = 'A' - 10;
    } else {
        return -1;
    }
    return (hex - offset) * base16Pows[position];
}

inline void reportFailed(int position, std::string reason)
{
    fprintf(stderr, "Failed at position %d\n", position);
    fprintf(stderr, "Reason: %s\n", reason.c_str());
}

int main()
{
    std::string ipString = "2001:0db8:0000:0000:0000:ff00:0042:8329";
    uint16_t ip[8] = {0};
    int ipPart = 7;
    int subPosition = 0;
    int sum = 0;

    for (int i = ipString.size() - 1; i >= 0; i--) {
        if (ipPart < 0) {
            reportFailed(i, "More than 8 sets");
            return 0;
        }
        if (ipString[i] == ':') {
            ip[ipPart] = sum;
            sum = 0;
            ipPart--;
            subPosition = 0;
        } else {
            int number = convertFromHex(ipString[i], subPosition);
            if (number == -1) {
                reportFailed(i, "Not Hex");
                return 0;
            }
            sum += number;
            if (sum > 0xFFFF) {
                reportFailed(i, "Hex too big");
                return 0;
            }
            subPosition++;
        }
    }

    ip[ipPart] = sum;
    fprintf(stdout, "Got number %x:%x:%x:%x:%x:%x:%x:%x\n", ip[0], ip[1], ip[2], ip[3], ip[4], ip[5], ip[6], ip[7]);

    return 0;
}