- for (ix = ixo = 0;;) {
- /*
- * Find the first changed line in the to-be-compacted file.
- * We need to keep track of both indexes, so if we find a
- * changed lines group on the other file, while scanning the
- * to-be-compacted file, we need to skip it properly. Note
- * that loops that are testing for changed lines on rchg* do
- * not need index bounding since the array is prepared with
- * a zero at position -1 and N.
- */
- for (; ix < nrec && !rchg[ix]; ix++)
- while (rchgo[ixo++]);
- if (ix == nrec)
- break;
+ long end;
+};
+
+/*
+ * Initialize g to point at the first group in xdf.
+ */
+static void group_init(xdfile_t *xdf, struct group *g)
+{
+ g->start = g->end = 0;
+ while (xdf->rchg[g->end])
+ g->end++;
+}
+
+/*
+ * Move g to describe the next (possibly empty) group in xdf and return 0. If g
+ * is already at the end of the file, do nothing and return -1.
+ */
+static inline int group_next(xdfile_t *xdf, struct group *g)
+{
+ if (g->end == xdf->nrec)
+ return -1;
+
+ g->start = g->end + 1;
+ for (g->end = g->start; xdf->rchg[g->end]; g->end++)
+ ;
+
+ return 0;
+}
+
+/*
+ * Move g to describe the previous (possibly empty) group in xdf and return 0.
+ * If g is already at the beginning of the file, do nothing and return -1.
+ */
+static inline int group_previous(xdfile_t *xdf, struct group *g)
+{
+ if (g->start == 0)
+ return -1;
+
+ g->end = g->start - 1;
+ for (g->start = g->end; xdf->rchg[g->start - 1]; g->start--)
+ ;
+
+ return 0;
+}
+
+/*
+ * If g can be slid toward the end of the file, do so, and if it bumps into a
+ * following group, expand this group to include it. Return 0 on success or -1
+ * if g cannot be slid down.
+ */
+static int group_slide_down(xdfile_t *xdf, struct group *g, long flags)
+{
+ if (g->end < xdf->nrec &&
+ recs_match(xdf->recs[g->start], xdf->recs[g->end], flags)) {
+ xdf->rchg[g->start++] = 0;
+ xdf->rchg[g->end++] = 1;
+
+ while (xdf->rchg[g->end])
+ g->end++;
+
+ return 0;
+ } else {
+ return -1;
+ }
+}
+
+/*
+ * If g can be slid toward the beginning of the file, do so, and if it bumps
+ * into a previous group, expand this group to include it. Return 0 on success
+ * or -1 if g cannot be slid up.
+ */
+static int group_slide_up(xdfile_t *xdf, struct group *g, long flags)
+{
+ if (g->start > 0 &&
+ recs_match(xdf->recs[g->start - 1], xdf->recs[g->end - 1], flags)) {
+ xdf->rchg[--g->start] = 1;
+ xdf->rchg[--g->end] = 0;
+
+ while (xdf->rchg[g->start - 1])
+ g->start--;
+
+ return 0;
+ } else {
+ return -1;
+ }
+}
+
+static void xdl_bug(const char *msg)
+{
+ fprintf(stderr, "BUG: %s\n", msg);
+ exit(1);
+}
+
+/*
+ * Move back and forward change groups for a consistent and pretty diff output.
+ * This also helps in finding joinable change groups and reducing the diff
+ * size.
+ */
+int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
+ struct group g, go;
+ long earliest_end, end_matching_other;
+ long groupsize;
+ unsigned int blank_lines;
+
+ group_init(xdf, &g);
+ group_init(xdfo, &go);
+
+ while (1) {
+ /* If the group is empty in the to-be-compacted file, skip it: */
+ if (g.end == g.start)
+ goto next;