old = a + len_a;
new = b + len_b;
sfx_length = 0;
- while (a <= old && b <= new && *old == *new) {
+ /*
+ * Note:
+ * if pfx_length is 0, old/new will never reach a - 1 because it
+ * would mean the whole string is common suffix. But then, the
+ * whole string would also be a common prefix, and we would not
+ * have pfx_length equals 0.
+ */
+ while (a + pfx_length - 1 <= old &&
+ b + pfx_length - 1 <= new &&
+ *old == *new) {
if (*old == '/')
sfx_length = len_a - (old - a);
old--;