text: #include <sys/socket.h>
  #include <arpa/inet.h>
  #include <ctype.h>
  #include <errno.h>
  #include <string.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]=0;
  			if (!*++s) break;
  			continue;
  		}
  		for (v=j=0; j<4 && (d=hexval(s[j]))>=0; j++)
  			v=16*v+d;
  		if (j==0) return 0;
  		ip[i] = 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;
  }
  