This code block does linear search, which can take O(n) time can we replace with pattern search considering domain sid strings would be similar, just few bytes would differ?

This may make few microsec difference but summation of microseconds can be significant in bigger enviornment.

#define WBC_MAXSUBAUTHS 15

fstring dom_sid;
#define FSTRING_LEN 256
typedef char fstring[FSTRING_LEN];

source3/passdb/machine_sid.c

int dom_sid_compare(const struct dom_sid *sid1, const struct dom_sid *sid2)
...
        for (i = sid1->num_auths-1; i >= 0; --i)
                if (sid1->sub_auths[i] != sid2->sub_auths[i])
                        return sid1->sub_auths[i] - sid2->sub_auths[i];