#include <arpa/inet.h>
#include <ctype.h>
#include <errno.h>
#include <string.h>
#include <sys/socket.h>

static int hexval(unsigned c) {
    if (c - '0' < 10)
        return c - '0';
    c |= 32;
    if (c - 'a' < 6)
        return c - 'a' + 10;
    return -1;
}

int inet_pton(int af, const char* restrict s, void* restrict a0) {
    uint16_t ip[8];
    unsigned char* a = a0;
    int i, j, v, d, brk = -1, need_v4 = 0;

    if (af == AF_INET) {
        for (i = 0; i < 4; i++) {
            for (v = j = 0; j < 3 && isdigit(s[j]); j++)
                v = 10 * v + s[j] - '0';
            if (j == 0 || (j > 1 && s[0] == '0') || v > 255)
                return 0;
            a[i] = v;
            if (s[j] == 0 && i == 3)
                return 1;
            if (s[j] != '.')
                return 0;
            s += j + 1;
        }
        return 0;
    } else if (af != AF_INET6) {
        errno = EAFNOSUPPORT;
        return -1;
    }

    if (*s == ':' && *++s != ':')
        return 0;

    for (i = 0;; i++) {
        if (s[0] == ':' && brk < 0) {
            brk = i;
            ip[i & 7] = 0;
            if (!*++s)
                break;
            if (i == 7)
                return 0;
            continue;
        }
        for (v = j = 0; j < 4 && (d = hexval(s[j])) >= 0; j++)
            v = 16 * v + d;
        if (j == 0)
            return 0;
        ip[i & 7] = v;
        if (!s[j] && (brk >= 0 || i == 7))
            break;
        if (i == 7)
            return 0;
        if (s[j] != ':') {
            if (s[j] != '.' || (i < 6 && brk < 0))
                return 0;
            need_v4 = 1;
            i++;
            break;
        }
        s += j + 1;
    }
    if (brk >= 0) {
        memmove(ip + brk + 7 - i, ip + brk, 2 * (i + 1 - brk));
        for (j = 0; j < 7 - i; j++)
            ip[brk + j] = 0;
    }
    for (j = 0; j < 8; j++) {
        *a++ = ip[j] >> 8;
        *a++ = ip[j];
    }
    if (need_v4 && inet_pton(AF_INET, (void*)s, a - 4) <= 0)
        return 0;
    return 1;
}