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-rw-r--r--bisect.c388
1 files changed, 388 insertions, 0 deletions
diff --git a/bisect.c b/bisect.c
new file mode 100644
index 000000000..27def7dac
--- /dev/null
+++ b/bisect.c
@@ -0,0 +1,388 @@
+#include "cache.h"
+#include "commit.h"
+#include "diff.h"
+#include "revision.h"
+#include "bisect.h"
+
+/* bits #0-15 in revision.h */
+
+#define COUNTED (1u<<16)
+
+/*
+ * This is a truly stupid algorithm, but it's only
+ * used for bisection, and we just don't care enough.
+ *
+ * We care just barely enough to avoid recursing for
+ * non-merge entries.
+ */
+static int count_distance(struct commit_list *entry)
+{
+ int nr = 0;
+
+ while (entry) {
+ struct commit *commit = entry->item;
+ struct commit_list *p;
+
+ if (commit->object.flags & (UNINTERESTING | COUNTED))
+ break;
+ if (!(commit->object.flags & TREESAME))
+ nr++;
+ commit->object.flags |= COUNTED;
+ p = commit->parents;
+ entry = p;
+ if (p) {
+ p = p->next;
+ while (p) {
+ nr += count_distance(p);
+ p = p->next;
+ }
+ }
+ }
+
+ return nr;
+}
+
+static void clear_distance(struct commit_list *list)
+{
+ while (list) {
+ struct commit *commit = list->item;
+ commit->object.flags &= ~COUNTED;
+ list = list->next;
+ }
+}
+
+#define DEBUG_BISECT 0
+
+static inline int weight(struct commit_list *elem)
+{
+ return *((int*)(elem->item->util));
+}
+
+static inline void weight_set(struct commit_list *elem, int weight)
+{
+ *((int*)(elem->item->util)) = weight;
+}
+
+static int count_interesting_parents(struct commit *commit)
+{
+ struct commit_list *p;
+ int count;
+
+ for (count = 0, p = commit->parents; p; p = p->next) {
+ if (p->item->object.flags & UNINTERESTING)
+ continue;
+ count++;
+ }
+ return count;
+}
+
+static inline int halfway(struct commit_list *p, int nr)
+{
+ /*
+ * Don't short-cut something we are not going to return!
+ */
+ if (p->item->object.flags & TREESAME)
+ return 0;
+ if (DEBUG_BISECT)
+ return 0;
+ /*
+ * 2 and 3 are halfway of 5.
+ * 3 is halfway of 6 but 2 and 4 are not.
+ */
+ switch (2 * weight(p) - nr) {
+ case -1: case 0: case 1:
+ return 1;
+ default:
+ return 0;
+ }
+}
+
+#if !DEBUG_BISECT
+#define show_list(a,b,c,d) do { ; } while (0)
+#else
+static void show_list(const char *debug, int counted, int nr,
+ struct commit_list *list)
+{
+ struct commit_list *p;
+
+ fprintf(stderr, "%s (%d/%d)\n", debug, counted, nr);
+
+ for (p = list; p; p = p->next) {
+ struct commit_list *pp;
+ struct commit *commit = p->item;
+ unsigned flags = commit->object.flags;
+ enum object_type type;
+ unsigned long size;
+ char *buf = read_sha1_file(commit->object.sha1, &type, &size);
+ char *ep, *sp;
+
+ fprintf(stderr, "%c%c%c ",
+ (flags & TREESAME) ? ' ' : 'T',
+ (flags & UNINTERESTING) ? 'U' : ' ',
+ (flags & COUNTED) ? 'C' : ' ');
+ if (commit->util)
+ fprintf(stderr, "%3d", weight(p));
+ else
+ fprintf(stderr, "---");
+ fprintf(stderr, " %.*s", 8, sha1_to_hex(commit->object.sha1));
+ for (pp = commit->parents; pp; pp = pp->next)
+ fprintf(stderr, " %.*s", 8,
+ sha1_to_hex(pp->item->object.sha1));
+
+ sp = strstr(buf, "\n\n");
+ if (sp) {
+ sp += 2;
+ for (ep = sp; *ep && *ep != '\n'; ep++)
+ ;
+ fprintf(stderr, " %.*s", (int)(ep - sp), sp);
+ }
+ fprintf(stderr, "\n");
+ }
+}
+#endif /* DEBUG_BISECT */
+
+static struct commit_list *best_bisection(struct commit_list *list, int nr)
+{
+ struct commit_list *p, *best;
+ int best_distance = -1;
+
+ best = list;
+ for (p = list; p; p = p->next) {
+ int distance;
+ unsigned flags = p->item->object.flags;
+
+ if (flags & TREESAME)
+ continue;
+ distance = weight(p);
+ if (nr - distance < distance)
+ distance = nr - distance;
+ if (distance > best_distance) {
+ best = p;
+ best_distance = distance;
+ }
+ }
+
+ return best;
+}
+
+struct commit_dist {
+ struct commit *commit;
+ int distance;
+};
+
+static int compare_commit_dist(const void *a_, const void *b_)
+{
+ struct commit_dist *a, *b;
+
+ a = (struct commit_dist *)a_;
+ b = (struct commit_dist *)b_;
+ if (a->distance != b->distance)
+ return b->distance - a->distance; /* desc sort */
+ return hashcmp(a->commit->object.sha1, b->commit->object.sha1);
+}
+
+static struct commit_list *best_bisection_sorted(struct commit_list *list, int nr)
+{
+ struct commit_list *p;
+ struct commit_dist *array = xcalloc(nr, sizeof(*array));
+ int cnt, i;
+
+ for (p = list, cnt = 0; p; p = p->next) {
+ int distance;
+ unsigned flags = p->item->object.flags;
+
+ if (flags & TREESAME)
+ continue;
+ distance = weight(p);
+ if (nr - distance < distance)
+ distance = nr - distance;
+ array[cnt].commit = p->item;
+ array[cnt].distance = distance;
+ cnt++;
+ }
+ qsort(array, cnt, sizeof(*array), compare_commit_dist);
+ for (p = list, i = 0; i < cnt; i++) {
+ struct name_decoration *r = xmalloc(sizeof(*r) + 100);
+ struct object *obj = &(array[i].commit->object);
+
+ sprintf(r->name, "dist=%d", array[i].distance);
+ r->next = add_decoration(&name_decoration, obj, r);
+ p->item = array[i].commit;
+ p = p->next;
+ }
+ if (p)
+ p->next = NULL;
+ free(array);
+ return list;
+}
+
+/*
+ * zero or positive weight is the number of interesting commits it can
+ * reach, including itself. Especially, weight = 0 means it does not
+ * reach any tree-changing commits (e.g. just above uninteresting one
+ * but traversal is with pathspec).
+ *
+ * weight = -1 means it has one parent and its distance is yet to
+ * be computed.
+ *
+ * weight = -2 means it has more than one parent and its distance is
+ * unknown. After running count_distance() first, they will get zero
+ * or positive distance.
+ */
+static struct commit_list *do_find_bisection(struct commit_list *list,
+ int nr, int *weights,
+ int find_all)
+{
+ int n, counted;
+ struct commit_list *p;
+
+ counted = 0;
+
+ for (n = 0, p = list; p; p = p->next) {
+ struct commit *commit = p->item;
+ unsigned flags = commit->object.flags;
+
+ p->item->util = &weights[n++];
+ switch (count_interesting_parents(commit)) {
+ case 0:
+ if (!(flags & TREESAME)) {
+ weight_set(p, 1);
+ counted++;
+ show_list("bisection 2 count one",
+ counted, nr, list);
+ }
+ /*
+ * otherwise, it is known not to reach any
+ * tree-changing commit and gets weight 0.
+ */
+ break;
+ case 1:
+ weight_set(p, -1);
+ break;
+ default:
+ weight_set(p, -2);
+ break;
+ }
+ }
+
+ show_list("bisection 2 initialize", counted, nr, list);
+
+ /*
+ * If you have only one parent in the resulting set
+ * then you can reach one commit more than that parent
+ * can reach. So we do not have to run the expensive
+ * count_distance() for single strand of pearls.
+ *
+ * However, if you have more than one parents, you cannot
+ * just add their distance and one for yourself, since
+ * they usually reach the same ancestor and you would
+ * end up counting them twice that way.
+ *
+ * So we will first count distance of merges the usual
+ * way, and then fill the blanks using cheaper algorithm.
+ */
+ for (p = list; p; p = p->next) {
+ if (p->item->object.flags & UNINTERESTING)
+ continue;
+ if (weight(p) != -2)
+ continue;
+ weight_set(p, count_distance(p));
+ clear_distance(list);
+
+ /* Does it happen to be at exactly half-way? */
+ if (!find_all && halfway(p, nr))
+ return p;
+ counted++;
+ }
+
+ show_list("bisection 2 count_distance", counted, nr, list);
+
+ while (counted < nr) {
+ for (p = list; p; p = p->next) {
+ struct commit_list *q;
+ unsigned flags = p->item->object.flags;
+
+ if (0 <= weight(p))
+ continue;
+ for (q = p->item->parents; q; q = q->next) {
+ if (q->item->object.flags & UNINTERESTING)
+ continue;
+ if (0 <= weight(q))
+ break;
+ }
+ if (!q)
+ continue;
+
+ /*
+ * weight for p is unknown but q is known.
+ * add one for p itself if p is to be counted,
+ * otherwise inherit it from q directly.
+ */
+ if (!(flags & TREESAME)) {
+ weight_set(p, weight(q)+1);
+ counted++;
+ show_list("bisection 2 count one",
+ counted, nr, list);
+ }
+ else
+ weight_set(p, weight(q));
+
+ /* Does it happen to be at exactly half-way? */
+ if (!find_all && halfway(p, nr))
+ return p;
+ }
+ }
+
+ show_list("bisection 2 counted all", counted, nr, list);
+
+ if (!find_all)
+ return best_bisection(list, nr);
+ else
+ return best_bisection_sorted(list, nr);
+}
+
+struct commit_list *find_bisection(struct commit_list *list,
+ int *reaches, int *all,
+ int find_all)
+{
+ int nr, on_list;
+ struct commit_list *p, *best, *next, *last;
+ int *weights;
+
+ show_list("bisection 2 entry", 0, 0, list);
+
+ /*
+ * Count the number of total and tree-changing items on the
+ * list, while reversing the list.
+ */
+ for (nr = on_list = 0, last = NULL, p = list;
+ p;
+ p = next) {
+ unsigned flags = p->item->object.flags;
+
+ next = p->next;
+ if (flags & UNINTERESTING)
+ continue;
+ p->next = last;
+ last = p;
+ if (!(flags & TREESAME))
+ nr++;
+ on_list++;
+ }
+ list = last;
+ show_list("bisection 2 sorted", 0, nr, list);
+
+ *all = nr;
+ weights = xcalloc(on_list, sizeof(*weights));
+
+ /* Do the real work of finding bisection commit. */
+ best = do_find_bisection(list, nr, weights, find_all);
+ if (best) {
+ if (!find_all)
+ best->next = NULL;
+ *reaches = weight(best);
+ }
+ free(weights);
+ return best;
+}
+
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