Function ip6_sprintf

freebsd/netinet6/in6.c:1635–1710

 */
static char digits[] = "0123456789abcdef";
char *
ip6_sprintf(char *ip6buf, const struct in6_addr *addr)
{
	int i, cnt = 0, maxcnt = 0, idx = 0, index = 0;
	char *cp;
	const u_int16_t *a = (const u_int16_t *)addr;
	const u_int8_t *d;
	int dcolon = 0, zero = 0;

	cp = ip6buf;

	for (i = 0; i < 8; i++) {
		if (*(a + i) == 0) {
			cnt++;
			if (cnt == 1)
				idx = i;
		}
		else if (maxcnt < cnt) {
			maxcnt = cnt;
			index = idx;
			cnt = 0;
		}
	}
	if (maxcnt < cnt) {
		maxcnt = cnt;
		index = idx;
	}

	for (i = 0; i < 8; i++) {
		if (dcolon == 1) {
			if (*a == 0) {
				if (i == 7)
					*cp++ = ':';
				a++;
				continue;
			} else
				dcolon = 2;
		}
		if (*a == 0) {
			if (dcolon == 0 && *(a + 1) == 0 && i == index) {
				if (i == 0)
					*cp++ = ':';
				*cp++ = ':';
				dcolon = 1;
			} else {
				*cp++ = '0';
				*cp++ = ':';
			}
			a++;
			continue;
		}
		d = (const u_char *)a;
		/* Try to eliminate leading zeros in printout like in :0001. */
		zero = 1;
		*cp = digits[*d >> 4];
		if (*cp != '0') {
			zero = 0;
			cp++;