The intent here is to get the highest multiple of four smaller or equal than i + 3. Instead of relying on integer division to get rid of the remainder just to "undo" everything, simply clear the lowest two bits (0b11 = 3) leaving multiples of four.
Index: ping.c =================================================================== RCS file: /cvs/src/sbin/ping/ping.c,v retrieving revision 1.218 diff -u -p -r1.218 ping.c --- ping.c 22 Feb 2017 13:43:35 -0000 1.218 +++ ping.c 13 Jun 2017 17:29:19 -0000 @@ -1379,7 +1379,7 @@ pr_ipopt(int hlen, u_char *buf) !memcmp(cp, old_rr, i) && !(options & F_FLOOD)) { (void)printf("\t(same route)"); - i = ((i + 3) / 4) * 4; + i = (i + 3) & ~0x3; hlen -= i; cp += i; break;