+
+ /* Lower bits of sline->flag records if the parent had this
+ * line, so XOR with all_mask gives us on-bits for parents we
+ * have differences with.
+ */
+ unsigned long common_adds = (sline->flag ^ all_mask) & all_mask;
+ unsigned long common_removes = all_mask;
+
+ /* If all the parents have this line, that also counts as
+ * having the same difference.
+ */
+ if (!common_adds)
+ common_adds = all_mask;
+
+ if (sline->lost_head) {
+ /* Lost head list records the lines removed from
+ * the parents, and parent_map records from which
+ * parent the line was removed.
+ */
+ struct lline *ll;
+ for (ll = sline->lost_head; ll; ll = ll->next) {
+ common_removes &= ll->parent_map;
+ }
+ }
+ return common_adds & common_removes;
+}
+
+static unsigned long line_all_diff(struct sline *sline, unsigned long all_mask)
+{
+ /*
+ * Look at the line and see from which parents we have some difference.
+ */
+ unsigned long different = (sline->flag ^ all_mask) & all_mask;