/* char *
 * inet_ntop(af, src, dst, size)
 *  convert a network format address to presentation format.
 * return:
 *  pointer to presentation format address (`dst'), or NULL (see errno).
 * author:
 *  Paul Vixie, 1996.
 */
const char *
inet_ntop(af, src, dst, size)
    int af;
    const void *src;
    char *dst;
    socklen_t size;
{
    switch (af) {
    case AF_INET:
        return (inet_ntop4(src, dst, size));
    case AF_INET6:
        return (inet_ntop6(src, dst, size));
    default:
        __set_errno (EAFNOSUPPORT);
        return (NULL);
    }
    /* NOTREACHED */
}
/* const char *
 * inet_ntop4(src, dst, size)
 *  format an IPv4 address
 * return:
 *  `dst' (as a const)
 * notes:
 *  (1) uses no statics
 *  (2) takes a u_char* not an in_addr as input
 * author:
 *  Paul Vixie, 1996.
 */
static const char *
internal_function
inet_ntop4(src, dst, size)
    const u_char *src;
    char *dst;
    socklen_t size;
{
    static const char fmt[] = "%u.%u.%u.%u";
    char tmp[sizeof "255.255.255.255"];
 
    if (SPRINTF((tmp, fmt, src[0], src[1], src[2], src[3])) >= size) {
        __set_errno (ENOSPC);
        return (NULL);
    }
    return strcpy(dst, tmp);
}
/* const char *
 * inet_ntop6(src, dst, size)
 *  convert IPv6 binary address into presentation (printable) format
 * author:
 *  Paul Vixie, 1996.
 */
static const char *
internal_function
inet_ntop6(src, dst, size)
    const u_char *src;
    char *dst;
    socklen_t size;
{
    /*
     * Note that int32_t and int16_t need only be "at least" large enough
     * to contain a value of the specified size.  On some systems, like
     * Crays, there is no such thing as an integer variable with 16 bits.
     * Keep this in mind if you think this function should have been coded
     * to use pointer overlays.  All the world's not a VAX.
     */
    char tmp[sizeof "ffff:ffff:ffff:ffff:ffff:ffff:255.255.255.255"], *tp;
    struct { int base, len; } best, cur;
    u_int words[NS_IN6ADDRSZ / NS_INT16SZ];
    int i;
 
    /*
     * Preprocess:
     *  Copy the input (bytewise) array into a wordwise array.
     *  Find the longest run of 0x00's in src[] for :: shorthanding.
     */
    memset(words, '', sizeof words);
    for (i = 0; i < NS_IN6ADDRSZ; i += 2)
        words[i / 2] = (src[i] << 8) | src[i + 1];
    best.base = -1;
    cur.base = -1;
    best.len = 0;
    cur.len = 0;
    for (i = 0; i < (NS_IN6ADDRSZ / NS_INT16SZ); i++) {
        if (words[i] == 0) {
            if (cur.base == -1)
                cur.base = i, cur.len = 1;
            else
                cur.len++;
        } else {
            if (cur.base != -1) {
                if (best.base == -1 || cur.len > best.len)
                    best = cur;
                cur.base = -1;
            }
        }
    }
    if (cur.base != -1) {
        if (best.base == -1 || cur.len > best.len)
            best = cur;
    }
    if (best.base != -1 && best.len < 2)
        best.base = -1;
 
    /*
     * Format the result.
     */
    tp = tmp;
    for (i = 0; i < (NS_IN6ADDRSZ / NS_INT16SZ); i++) {
        /* Are we inside the best run of 0x00's? */
        if (best.base != -1 && i >= best.base &&
            i < (best.base + best.len)) {
            if (i == best.base)
                *tp++ = ':';
            continue;
        }
        /* Are we following an initial run of 0x00s or any real hex? */
        if (i != 0)
            *tp++ = ':';
        /* Is this address an encapsulated IPv4? */
        if (i == 6 && best.base == 0 &&
            (best.len == 6 || (best.len == 5 && words[5] == 0xffff))) {
            if (!inet_ntop4(src+12, tp, sizeof tmp - (tp - tmp)))
                return (NULL);
            tp += strlen(tp);
            break;
        }
        tp += SPRINTF((tp, "%x", words[i]));
    }
    /* Was it a trailing run of 0x00's? */
    if (best.base != -1 && (best.base + best.len) ==
        (NS_IN6ADDRSZ / NS_INT16SZ))
        *tp++ = ':';
    *tp++ = '';
 
    /*
     * Check for overflow, copy, and we're done.
     */
    if ((socklen_t)(tp - tmp) > size) {
        __set_errno (ENOSPC);
        return (NULL);
    }
    return strcpy(dst, tmp);
}