builtin/clone: allow remote helpers to detect repo

[alt-git.git] / commit-reach.c

#include "git-compat-util.h"
#include "commit.h"
#include "commit-graph.h"
#include "decorate.h"
#include "hex.h"
#include "prio-queue.h"
#include "ref-filter.h"
#include "revision.h"
#include "tag.h"
#include "commit-reach.h"
#include "ewah/ewok.h"

/* Remember to update object flag allocation in object.h */
#define PARENT1         (1u<<16)
#define PARENT2         (1u<<17)
#define STALE           (1u<<18)
#define RESULT          (1u<<19)

static const unsigned all_flags = (PARENT1 | PARENT2 | STALE | RESULT);

static int compare_commits_by_gen(const void *_a, const void *_b)
{
        const struct commit *a = *(const struct commit * const *)_a;
        const struct commit *b = *(const struct commit * const *)_b;

        timestamp_t generation_a = commit_graph_generation(a);
        timestamp_t generation_b = commit_graph_generation(b);

        if (generation_a < generation_b)
                return -1;
        if (generation_a > generation_b)
                return 1;
        if (a->date < b->date)
                return -1;
        if (a->date > b->date)
                return 1;
        return 0;
}

static int queue_has_nonstale(struct prio_queue *queue)
{
        int i;
        for (i = 0; i < queue->nr; i++) {
                struct commit *commit = queue->array[i].data;
                if (!(commit->object.flags & STALE))
                        return 1;
        }
        return 0;
}

/* all input commits in one and twos[] must have been parsed! */
static struct commit_list *paint_down_to_common(struct repository *r,
                                                struct commit *one, int n,
                                                struct commit **twos,
                                                timestamp_t min_generation)
{
        struct prio_queue queue = { compare_commits_by_gen_then_commit_date };
        struct commit_list *result = NULL;
        int i;
        timestamp_t last_gen = GENERATION_NUMBER_INFINITY;

        if (!min_generation && !corrected_commit_dates_enabled(r))
                queue.compare = compare_commits_by_commit_date;

        one->object.flags |= PARENT1;
        if (!n) {
                commit_list_append(one, &result);
                return result;
        }
        prio_queue_put(&queue, one);

        for (i = 0; i < n; i++) {
                twos[i]->object.flags |= PARENT2;
                prio_queue_put(&queue, twos[i]);
        }

        while (queue_has_nonstale(&queue)) {
                struct commit *commit = prio_queue_get(&queue);
                struct commit_list *parents;
                int flags;
                timestamp_t generation = commit_graph_generation(commit);

                if (min_generation && generation > last_gen)
                        BUG("bad generation skip %"PRItime" > %"PRItime" at %s",
                            generation, last_gen,
                            oid_to_hex(&commit->object.oid));
                last_gen = generation;

                if (generation < min_generation)
                        break;

                flags = commit->object.flags & (PARENT1 | PARENT2 | STALE);
                if (flags == (PARENT1 | PARENT2)) {
                        if (!(commit->object.flags & RESULT)) {
                                commit->object.flags |= RESULT;
                                commit_list_insert_by_date(commit, &result);
                        }
                        /* Mark parents of a found merge stale */
                        flags |= STALE;
                }
                parents = commit->parents;
                while (parents) {
                        struct commit *p = parents->item;
                        parents = parents->next;
                        if ((p->object.flags & flags) == flags)
                                continue;
                        if (repo_parse_commit(r, p))
                                return NULL;
                        p->object.flags |= flags;
                        prio_queue_put(&queue, p);
                }
        }

        clear_prio_queue(&queue);
        return result;
}

static struct commit_list *merge_bases_many(struct repository *r,
                                            struct commit *one, int n,
                                            struct commit **twos)
{
        struct commit_list *list = NULL;
        struct commit_list *result = NULL;
        int i;

        for (i = 0; i < n; i++) {
                if (one == twos[i])
                        /*
                         * We do not mark this even with RESULT so we do not
                         * have to clean it up.
                         */
                        return commit_list_insert(one, &result);
        }

        if (repo_parse_commit(r, one))
                return NULL;
        for (i = 0; i < n; i++) {
                if (repo_parse_commit(r, twos[i]))
                        return NULL;
        }

        list = paint_down_to_common(r, one, n, twos, 0);

        while (list) {
                struct commit *commit = pop_commit(&list);
                if (!(commit->object.flags & STALE))
                        commit_list_insert_by_date(commit, &result);
        }
        return result;
}

struct commit_list *get_octopus_merge_bases(struct commit_list *in)
{
        struct commit_list *i, *j, *k, *ret = NULL;

        if (!in)
                return ret;

        commit_list_insert(in->item, &ret);

        for (i = in->next; i; i = i->next) {
                struct commit_list *new_commits = NULL, *end = NULL;

                for (j = ret; j; j = j->next) {
                        struct commit_list *bases;
                        bases = repo_get_merge_bases(the_repository, i->item,
                                                     j->item);
                        if (!new_commits)
                                new_commits = bases;
                        else
                                end->next = bases;
                        for (k = bases; k; k = k->next)
                                end = k;
                }
                free_commit_list(ret);
                ret = new_commits;
        }
        return ret;
}

static int remove_redundant_no_gen(struct repository *r,
                                   struct commit **array, int cnt)
{
        struct commit **work;
        unsigned char *redundant;
        int *filled_index;
        int i, j, filled;

        CALLOC_ARRAY(work, cnt);
        redundant = xcalloc(cnt, 1);
        ALLOC_ARRAY(filled_index, cnt - 1);

        for (i = 0; i < cnt; i++)
                repo_parse_commit(r, array[i]);
        for (i = 0; i < cnt; i++) {
                struct commit_list *common;
                timestamp_t min_generation = commit_graph_generation(array[i]);

                if (redundant[i])
                        continue;
                for (j = filled = 0; j < cnt; j++) {
                        timestamp_t curr_generation;
                        if (i == j || redundant[j])
                                continue;
                        filled_index[filled] = j;
                        work[filled++] = array[j];

                        curr_generation = commit_graph_generation(array[j]);
                        if (curr_generation < min_generation)
                                min_generation = curr_generation;
                }
                common = paint_down_to_common(r, array[i], filled,
                                              work, min_generation);
                if (array[i]->object.flags & PARENT2)
                        redundant[i] = 1;
                for (j = 0; j < filled; j++)
                        if (work[j]->object.flags & PARENT1)
                                redundant[filled_index[j]] = 1;
                clear_commit_marks(array[i], all_flags);
                clear_commit_marks_many(filled, work, all_flags);
                free_commit_list(common);
        }

        /* Now collect the result */
        COPY_ARRAY(work, array, cnt);
        for (i = filled = 0; i < cnt; i++)
                if (!redundant[i])
                        array[filled++] = work[i];
        free(work);
        free(redundant);
        free(filled_index);
        return filled;
}

static int remove_redundant_with_gen(struct repository *r,
                                     struct commit **array, int cnt)
{
        int i, count_non_stale = 0, count_still_independent = cnt;
        timestamp_t min_generation = GENERATION_NUMBER_INFINITY;
        struct commit **walk_start, **sorted;
        size_t walk_start_nr = 0, walk_start_alloc = cnt;
        int min_gen_pos = 0;

        /*
         * Sort the input by generation number, ascending. This allows
         * us to increase the "min_generation" limit when we discover
         * the commit with lowest generation is STALE. The index
         * min_gen_pos points to the current position within 'array'
         * that is not yet known to be STALE.
         */
        DUP_ARRAY(sorted, array, cnt);
        QSORT(sorted, cnt, compare_commits_by_gen);
        min_generation = commit_graph_generation(sorted[0]);

        ALLOC_ARRAY(walk_start, walk_start_alloc);

        /* Mark all parents of the input as STALE */
        for (i = 0; i < cnt; i++) {
                struct commit_list *parents;

                repo_parse_commit(r, array[i]);
                array[i]->object.flags |= RESULT;
                parents = array[i]->parents;

                while (parents) {
                        repo_parse_commit(r, parents->item);
                        if (!(parents->item->object.flags & STALE)) {
                                parents->item->object.flags |= STALE;
                                ALLOC_GROW(walk_start, walk_start_nr + 1, walk_start_alloc);
                                walk_start[walk_start_nr++] = parents->item;
                        }
                        parents = parents->next;
                }
        }

        QSORT(walk_start, walk_start_nr, compare_commits_by_gen);

        /* remove STALE bit for now to allow walking through parents */
        for (i = 0; i < walk_start_nr; i++)
                walk_start[i]->object.flags &= ~STALE;

        /*
         * Start walking from the highest generation. Hopefully, it will
         * find all other items during the first-parent walk, and we can
         * terminate early. Otherwise, we will do the same amount of work
         * as before.
         */
        for (i = walk_start_nr - 1; i >= 0 && count_still_independent > 1; i--) {
                /* push the STALE bits up to min generation */
                struct commit_list *stack = NULL;

                commit_list_insert(walk_start[i], &stack);
                walk_start[i]->object.flags |= STALE;

                while (stack) {
                        struct commit_list *parents;
                        struct commit *c = stack->item;

                        repo_parse_commit(r, c);

                        if (c->object.flags & RESULT) {
                                c->object.flags &= ~RESULT;
                                if (--count_still_independent <= 1)
                                        break;
                                if (oideq(&c->object.oid, &sorted[min_gen_pos]->object.oid)) {
                                        while (min_gen_pos < cnt - 1 &&
                                               (sorted[min_gen_pos]->object.flags & STALE))
                                                min_gen_pos++;
                                        min_generation = commit_graph_generation(sorted[min_gen_pos]);
                                }
                        }

                        if (commit_graph_generation(c) < min_generation) {
                                pop_commit(&stack);
                                continue;
                        }

                        parents = c->parents;
                        while (parents) {
                                if (!(parents->item->object.flags & STALE)) {
                                        parents->item->object.flags |= STALE;
                                        commit_list_insert(parents->item, &stack);
                                        break;
                                }
                                parents = parents->next;
                        }

                        /* pop if all parents have been visited already */
                        if (!parents)
                                pop_commit(&stack);
                }
                free_commit_list(stack);
        }
        free(sorted);

        /* clear result */
        for (i = 0; i < cnt; i++)
                array[i]->object.flags &= ~RESULT;

        /* rearrange array */
        for (i = count_non_stale = 0; i < cnt; i++) {
                if (!(array[i]->object.flags & STALE))
                        array[count_non_stale++] = array[i];
        }

        /* clear marks */
        clear_commit_marks_many(walk_start_nr, walk_start, STALE);
        free(walk_start);

        return count_non_stale;
}

static int remove_redundant(struct repository *r, struct commit **array, int cnt)
{
        /*
         * Some commit in the array may be an ancestor of
         * another commit.  Move the independent commits to the
         * beginning of 'array' and return their number. Callers
         * should not rely upon the contents of 'array' after
         * that number.
         */
        if (generation_numbers_enabled(r)) {
                int i;

                /*
                 * If we have a single commit with finite generation
                 * number, then the _with_gen algorithm is preferred.
                 */
                for (i = 0; i < cnt; i++) {
                        if (commit_graph_generation(array[i]) < GENERATION_NUMBER_INFINITY)
                                return remove_redundant_with_gen(r, array, cnt);
                }
        }

        return remove_redundant_no_gen(r, array, cnt);
}

static struct commit_list *get_merge_bases_many_0(struct repository *r,
                                                  struct commit *one,
                                                  int n,
                                                  struct commit **twos,
                                                  int cleanup)
{
        struct commit_list *list;
        struct commit **rslt;
        struct commit_list *result;
        int cnt, i;

        result = merge_bases_many(r, one, n, twos);
        for (i = 0; i < n; i++) {
                if (one == twos[i])
                        return result;
        }
        if (!result || !result->next) {
                if (cleanup) {
                        clear_commit_marks(one, all_flags);
                        clear_commit_marks_many(n, twos, all_flags);
                }
                return result;
        }

        /* There are more than one */
        cnt = commit_list_count(result);
        CALLOC_ARRAY(rslt, cnt);
        for (list = result, i = 0; list; list = list->next)
                rslt[i++] = list->item;
        free_commit_list(result);

        clear_commit_marks(one, all_flags);
        clear_commit_marks_many(n, twos, all_flags);

        cnt = remove_redundant(r, rslt, cnt);
        result = NULL;
        for (i = 0; i < cnt; i++)
                commit_list_insert_by_date(rslt[i], &result);
        free(rslt);
        return result;
}

struct commit_list *repo_get_merge_bases_many(struct repository *r,
                                              struct commit *one,
                                              int n,
                                              struct commit **twos)
{
        return get_merge_bases_many_0(r, one, n, twos, 1);
}

struct commit_list *repo_get_merge_bases_many_dirty(struct repository *r,
                                                    struct commit *one,
                                                    int n,
                                                    struct commit **twos)
{
        return get_merge_bases_many_0(r, one, n, twos, 0);
}

struct commit_list *repo_get_merge_bases(struct repository *r,
                                         struct commit *one,
                                         struct commit *two)
{
        return get_merge_bases_many_0(r, one, 1, &two, 1);
}

/*
 * Is "commit" a descendant of one of the elements on the "with_commit" list?
 */
int repo_is_descendant_of(struct repository *r,
                          struct commit *commit,
                          struct commit_list *with_commit)
{
        if (!with_commit)
                return 1;

        if (generation_numbers_enabled(r)) {
                struct commit_list *from_list = NULL;
                int result;
                commit_list_insert(commit, &from_list);
                result = can_all_from_reach(from_list, with_commit, 0);
                free_commit_list(from_list);
                return result;
        } else {
                while (with_commit) {
                        struct commit *other;

                        other = with_commit->item;
                        with_commit = with_commit->next;
                        if (repo_in_merge_bases_many(r, other, 1, &commit))
                                return 1;
                }
                return 0;
        }
}

/*
 * Is "commit" an ancestor of one of the "references"?
 */
int repo_in_merge_bases_many(struct repository *r, struct commit *commit,
                             int nr_reference, struct commit **reference)
{
        struct commit_list *bases;
        int ret = 0, i;
        timestamp_t generation, max_generation = GENERATION_NUMBER_ZERO;

        if (repo_parse_commit(r, commit))
                return ret;
        for (i = 0; i < nr_reference; i++) {
                if (repo_parse_commit(r, reference[i]))
                        return ret;

                generation = commit_graph_generation(reference[i]);
                if (generation > max_generation)
                        max_generation = generation;
        }

        generation = commit_graph_generation(commit);
        if (generation > max_generation)
                return ret;

        bases = paint_down_to_common(r, commit,
                                     nr_reference, reference,
                                     generation);
        if (commit->object.flags & PARENT2)
                ret = 1;
        clear_commit_marks(commit, all_flags);
        clear_commit_marks_many(nr_reference, reference, all_flags);
        free_commit_list(bases);
        return ret;
}

/*
 * Is "commit" an ancestor of (i.e. reachable from) the "reference"?
 */
int repo_in_merge_bases(struct repository *r,
                        struct commit *commit,
                        struct commit *reference)
{
        int res;
        struct commit_list *list = NULL;
        struct commit_list **next = &list;

        next = commit_list_append(commit, next);
        res = repo_is_descendant_of(r, reference, list);
        free_commit_list(list);

        return res;
}

struct commit_list *reduce_heads(struct commit_list *heads)
{
        struct commit_list *p;
        struct commit_list *result = NULL, **tail = &result;
        struct commit **array;
        int num_head, i;

        if (!heads)
                return NULL;

        /* Uniquify */
        for (p = heads; p; p = p->next)
                p->item->object.flags &= ~STALE;
        for (p = heads, num_head = 0; p; p = p->next) {
                if (p->item->object.flags & STALE)
                        continue;
                p->item->object.flags |= STALE;
                num_head++;
        }
        CALLOC_ARRAY(array, num_head);
        for (p = heads, i = 0; p; p = p->next) {
                if (p->item->object.flags & STALE) {
                        array[i++] = p->item;
                        p->item->object.flags &= ~STALE;
                }
        }
        num_head = remove_redundant(the_repository, array, num_head);
        for (i = 0; i < num_head; i++)
                tail = &commit_list_insert(array[i], tail)->next;
        free(array);
        return result;
}

void reduce_heads_replace(struct commit_list **heads)
{
        struct commit_list *result = reduce_heads(*heads);
        free_commit_list(*heads);
        *heads = result;
}

int ref_newer(const struct object_id *new_oid, const struct object_id *old_oid)
{
        struct object *o;
        struct commit *old_commit, *new_commit;
        struct commit_list *old_commit_list = NULL;
        int ret;

        /*
         * Both new_commit and old_commit must be commit-ish and new_commit is descendant of
         * old_commit.  Otherwise we require --force.
         */
        o = deref_tag(the_repository, parse_object(the_repository, old_oid),
                      NULL, 0);
        if (!o || o->type != OBJ_COMMIT)
                return 0;
        old_commit = (struct commit *) o;

        o = deref_tag(the_repository, parse_object(the_repository, new_oid),
                      NULL, 0);
        if (!o || o->type != OBJ_COMMIT)
                return 0;
        new_commit = (struct commit *) o;

        if (repo_parse_commit(the_repository, new_commit) < 0)
                return 0;

        commit_list_insert(old_commit, &old_commit_list);
        ret = repo_is_descendant_of(the_repository,
                                    new_commit, old_commit_list);
        free_commit_list(old_commit_list);
        return ret;
}

/*
 * Mimicking the real stack, this stack lives on the heap, avoiding stack
 * overflows.
 *
 * At each recursion step, the stack items points to the commits whose
 * ancestors are to be inspected.
 */
struct contains_stack {
        int nr, alloc;
        struct contains_stack_entry {
                struct commit *commit;
                struct commit_list *parents;
        } *contains_stack;
};

static int in_commit_list(const struct commit_list *want, struct commit *c)
{
        for (; want; want = want->next)
                if (oideq(&want->item->object.oid, &c->object.oid))
                        return 1;
        return 0;
}

/*
 * Test whether the candidate is contained in the list.
 * Do not recurse to find out, though, but return -1 if inconclusive.
 */
static enum contains_result contains_test(struct commit *candidate,
                                          const struct commit_list *want,
                                          struct contains_cache *cache,
                                          timestamp_t cutoff)
{
        enum contains_result *cached = contains_cache_at(cache, candidate);

        /* If we already have the answer cached, return that. */
        if (*cached)
                return *cached;

        /* or are we it? */
        if (in_commit_list(want, candidate)) {
                *cached = CONTAINS_YES;
                return CONTAINS_YES;
        }

        /* Otherwise, we don't know; prepare to recurse */
        parse_commit_or_die(candidate);

        if (commit_graph_generation(candidate) < cutoff)
                return CONTAINS_NO;

        return CONTAINS_UNKNOWN;
}

static void push_to_contains_stack(struct commit *candidate, struct contains_stack *contains_stack)
{
        ALLOC_GROW(contains_stack->contains_stack, contains_stack->nr + 1, contains_stack->alloc);
        contains_stack->contains_stack[contains_stack->nr].commit = candidate;
        contains_stack->contains_stack[contains_stack->nr++].parents = candidate->parents;
}

static enum contains_result contains_tag_algo(struct commit *candidate,
                                              const struct commit_list *want,
                                              struct contains_cache *cache)
{
        struct contains_stack contains_stack = { 0, 0, NULL };
        enum contains_result result;
        timestamp_t cutoff = GENERATION_NUMBER_INFINITY;
        const struct commit_list *p;

        for (p = want; p; p = p->next) {
                timestamp_t generation;
                struct commit *c = p->item;
                load_commit_graph_info(the_repository, c);
                generation = commit_graph_generation(c);
                if (generation < cutoff)
                        cutoff = generation;
        }

        result = contains_test(candidate, want, cache, cutoff);
        if (result != CONTAINS_UNKNOWN)
                return result;

        push_to_contains_stack(candidate, &contains_stack);
        while (contains_stack.nr) {
                struct contains_stack_entry *entry = &contains_stack.contains_stack[contains_stack.nr - 1];
                struct commit *commit = entry->commit;
                struct commit_list *parents = entry->parents;

                if (!parents) {
                        *contains_cache_at(cache, commit) = CONTAINS_NO;
                        contains_stack.nr--;
                }
                /*
                 * If we just popped the stack, parents->item has been marked,
                 * therefore contains_test will return a meaningful yes/no.
                 */
                else switch (contains_test(parents->item, want, cache, cutoff)) {
                case CONTAINS_YES:
                        *contains_cache_at(cache, commit) = CONTAINS_YES;
                        contains_stack.nr--;
                        break;
                case CONTAINS_NO:
                        entry->parents = parents->next;
                        break;
                case CONTAINS_UNKNOWN:
                        push_to_contains_stack(parents->item, &contains_stack);
                        break;
                }
        }
        free(contains_stack.contains_stack);
        return contains_test(candidate, want, cache, cutoff);
}

int commit_contains(struct ref_filter *filter, struct commit *commit,
                    struct commit_list *list, struct contains_cache *cache)
{
        if (filter->with_commit_tag_algo)
                return contains_tag_algo(commit, list, cache) == CONTAINS_YES;
        return repo_is_descendant_of(the_repository, commit, list);
}

int can_all_from_reach_with_flag(struct object_array *from,
                                 unsigned int with_flag,
                                 unsigned int assign_flag,
                                 time_t min_commit_date,
                                 timestamp_t min_generation)
{
        struct commit **list = NULL;
        int i;
        int nr_commits;
        int result = 1;

        ALLOC_ARRAY(list, from->nr);
        nr_commits = 0;
        for (i = 0; i < from->nr; i++) {
                struct object *from_one = from->objects[i].item;

                if (!from_one || from_one->flags & assign_flag)
                        continue;

                from_one = deref_tag(the_repository, from_one,
                                     "a from object", 0);
                if (!from_one || from_one->type != OBJ_COMMIT) {
                        /*
                         * no way to tell if this is reachable by
                         * looking at the ancestry chain alone, so
                         * leave a note to ourselves not to worry about
                         * this object anymore.
                         */
                        from->objects[i].item->flags |= assign_flag;
                        continue;
                }

                list[nr_commits] = (struct commit *)from_one;
                if (repo_parse_commit(the_repository, list[nr_commits]) ||
                    commit_graph_generation(list[nr_commits]) < min_generation) {
                        result = 0;
                        goto cleanup;
                }

                nr_commits++;
        }

        QSORT(list, nr_commits, compare_commits_by_gen);

        for (i = 0; i < nr_commits; i++) {
                /* DFS from list[i] */
                struct commit_list *stack = NULL;

                list[i]->object.flags |= assign_flag;
                commit_list_insert(list[i], &stack);

                while (stack) {
                        struct commit_list *parent;

                        if (stack->item->object.flags & (with_flag | RESULT)) {
                                pop_commit(&stack);
                                if (stack)
                                        stack->item->object.flags |= RESULT;
                                continue;
                        }

                        for (parent = stack->item->parents; parent; parent = parent->next) {
                                if (parent->item->object.flags & (with_flag | RESULT))
                                        stack->item->object.flags |= RESULT;

                                if (!(parent->item->object.flags & assign_flag)) {
                                        parent->item->object.flags |= assign_flag;

                                        if (repo_parse_commit(the_repository, parent->item) ||
                                            parent->item->date < min_commit_date ||
                                            commit_graph_generation(parent->item) < min_generation)
                                                continue;

                                        commit_list_insert(parent->item, &stack);
                                        break;
                                }
                        }

                        if (!parent)
                                pop_commit(&stack);
                }

                if (!(list[i]->object.flags & (with_flag | RESULT))) {
                        result = 0;
                        goto cleanup;
                }
        }

cleanup:
        clear_commit_marks_many(nr_commits, list, RESULT | assign_flag);
        free(list);

        for (i = 0; i < from->nr; i++) {
                struct object *from_one = from->objects[i].item;

                if (from_one)
                        from_one->flags &= ~assign_flag;
        }

        return result;
}

int can_all_from_reach(struct commit_list *from, struct commit_list *to,
                       int cutoff_by_min_date)
{
        struct object_array from_objs = OBJECT_ARRAY_INIT;
        time_t min_commit_date = cutoff_by_min_date ? from->item->date : 0;
        struct commit_list *from_iter = from, *to_iter = to;
        int result;
        timestamp_t min_generation = GENERATION_NUMBER_INFINITY;

        while (from_iter) {
                add_object_array(&from_iter->item->object, NULL, &from_objs);

                if (!repo_parse_commit(the_repository, from_iter->item)) {
                        timestamp_t generation;
                        if (from_iter->item->date < min_commit_date)
                                min_commit_date = from_iter->item->date;

                        generation = commit_graph_generation(from_iter->item);
                        if (generation < min_generation)
                                min_generation = generation;
                }

                from_iter = from_iter->next;
        }

        while (to_iter) {
                if (!repo_parse_commit(the_repository, to_iter->item)) {
                        timestamp_t generation;
                        if (to_iter->item->date < min_commit_date)
                                min_commit_date = to_iter->item->date;

                        generation = commit_graph_generation(to_iter->item);
                        if (generation < min_generation)
                                min_generation = generation;
                }

                to_iter->item->object.flags |= PARENT2;

                to_iter = to_iter->next;
        }

        result = can_all_from_reach_with_flag(&from_objs, PARENT2, PARENT1,
                                              min_commit_date, min_generation);

        while (from) {
                clear_commit_marks(from->item, PARENT1);
                from = from->next;
        }

        while (to) {
                clear_commit_marks(to->item, PARENT2);
                to = to->next;
        }

        object_array_clear(&from_objs);
        return result;
}

struct commit_list *get_reachable_subset(struct commit **from, int nr_from,
                                         struct commit **to, int nr_to,
                                         unsigned int reachable_flag)
{
        struct commit **item;
        struct commit *current;
        struct commit_list *found_commits = NULL;
        struct commit **to_last = to + nr_to;
        struct commit **from_last = from + nr_from;
        timestamp_t min_generation = GENERATION_NUMBER_INFINITY;
        int num_to_find = 0;

        struct prio_queue queue = { compare_commits_by_gen_then_commit_date };

        for (item = to; item < to_last; item++) {
                timestamp_t generation;
                struct commit *c = *item;

                repo_parse_commit(the_repository, c);
                generation = commit_graph_generation(c);
                if (generation < min_generation)
                        min_generation = generation;

                if (!(c->object.flags & PARENT1)) {
                        c->object.flags |= PARENT1;
                        num_to_find++;
                }
        }

        for (item = from; item < from_last; item++) {
                struct commit *c = *item;
                if (!(c->object.flags & PARENT2)) {
                        c->object.flags |= PARENT2;
                        repo_parse_commit(the_repository, c);

                        prio_queue_put(&queue, *item);
                }
        }

        while (num_to_find && (current = prio_queue_get(&queue)) != NULL) {
                struct commit_list *parents;

                if (current->object.flags & PARENT1) {
                        current->object.flags &= ~PARENT1;
                        current->object.flags |= reachable_flag;
                        commit_list_insert(current, &found_commits);
                        num_to_find--;
                }

                for (parents = current->parents; parents; parents = parents->next) {
                        struct commit *p = parents->item;

                        repo_parse_commit(the_repository, p);

                        if (commit_graph_generation(p) < min_generation)
                                continue;

                        if (p->object.flags & PARENT2)
                                continue;

                        p->object.flags |= PARENT2;
                        prio_queue_put(&queue, p);
                }
        }

        clear_prio_queue(&queue);

        clear_commit_marks_many(nr_to, to, PARENT1);
        clear_commit_marks_many(nr_from, from, PARENT2);

        return found_commits;
}

define_commit_slab(bit_arrays, struct bitmap *);
static struct bit_arrays bit_arrays;

static void insert_no_dup(struct prio_queue *queue, struct commit *c)
{
        if (c->object.flags & PARENT2)
                return;
        prio_queue_put(queue, c);
        c->object.flags |= PARENT2;
}

static struct bitmap *get_bit_array(struct commit *c, int width)
{
        struct bitmap **bitmap = bit_arrays_at(&bit_arrays, c);
        if (!*bitmap)
                *bitmap = bitmap_word_alloc(width);
        return *bitmap;
}

static void free_bit_array(struct commit *c)
{
        struct bitmap **bitmap = bit_arrays_at(&bit_arrays, c);
        if (!*bitmap)
                return;
        bitmap_free(*bitmap);
        *bitmap = NULL;
}

void ahead_behind(struct repository *r,
                  struct commit **commits, size_t commits_nr,
                  struct ahead_behind_count *counts, size_t counts_nr)
{
        struct prio_queue queue = { .compare = compare_commits_by_gen_then_commit_date };
        size_t width = DIV_ROUND_UP(commits_nr, BITS_IN_EWORD);

        if (!commits_nr || !counts_nr)
                return;

        for (size_t i = 0; i < counts_nr; i++) {
                counts[i].ahead = 0;
                counts[i].behind = 0;
        }

        ensure_generations_valid(r, commits, commits_nr);

        init_bit_arrays(&bit_arrays);

        for (size_t i = 0; i < commits_nr; i++) {
                struct commit *c = commits[i];
                struct bitmap *bitmap = get_bit_array(c, width);

                bitmap_set(bitmap, i);
                insert_no_dup(&queue, c);
        }

        while (queue_has_nonstale(&queue)) {
                struct commit *c = prio_queue_get(&queue);
                struct commit_list *p;
                struct bitmap *bitmap_c = get_bit_array(c, width);

                for (size_t i = 0; i < counts_nr; i++) {
                        int reach_from_tip = !!bitmap_get(bitmap_c, counts[i].tip_index);
                        int reach_from_base = !!bitmap_get(bitmap_c, counts[i].base_index);

                        if (reach_from_tip ^ reach_from_base) {
                                if (reach_from_base)
                                        counts[i].behind++;
                                else
                                        counts[i].ahead++;
                        }
                }

                for (p = c->parents; p; p = p->next) {
                        struct bitmap *bitmap_p;

                        repo_parse_commit(r, p->item);

                        bitmap_p = get_bit_array(p->item, width);
                        bitmap_or(bitmap_p, bitmap_c);

                        /*
                         * If this parent is reachable from every starting
                         * commit, then none of its ancestors can contribute
                         * to the ahead/behind count. Mark it as STALE, so
                         * we can stop the walk when every commit in the
                         * queue is STALE.
                         */
                        if (bitmap_popcount(bitmap_p) == commits_nr)
                                p->item->object.flags |= STALE;

                        insert_no_dup(&queue, p->item);
                }

                free_bit_array(c);
        }

        /* STALE is used here, PARENT2 is used by insert_no_dup(). */
        repo_clear_commit_marks(r, PARENT2 | STALE);
        clear_bit_arrays(&bit_arrays);
        clear_prio_queue(&queue);
}

struct commit_and_index {
        struct commit *commit;
        unsigned int index;
        timestamp_t generation;
};

static int compare_commit_and_index_by_generation(const void *va, const void *vb)
{
        const struct commit_and_index *a = (const struct commit_and_index *)va;
        const struct commit_and_index *b = (const struct commit_and_index *)vb;

        if (a->generation > b->generation)
                return 1;
        if (a->generation < b->generation)
                return -1;
        return 0;
}

void tips_reachable_from_bases(struct repository *r,
                               struct commit_list *bases,
                               struct commit **tips, size_t tips_nr,
                               int mark)
{
        struct commit_and_index *commits;
        size_t min_generation_index = 0;
        timestamp_t min_generation;
        struct commit_list *stack = NULL;

        if (!bases || !tips || !tips_nr)
                return;

        /*
         * Do a depth-first search starting at 'bases' to search for the
         * tips. Stop at the lowest (un-found) generation number. When
         * finding the lowest commit, increase the minimum generation
         * number to the next lowest (un-found) generation number.
         */

        CALLOC_ARRAY(commits, tips_nr);

        for (size_t i = 0; i < tips_nr; i++) {
                commits[i].commit = tips[i];
                commits[i].index = i;
                commits[i].generation = commit_graph_generation(tips[i]);
        }

        /* Sort with generation number ascending. */
        QSORT(commits, tips_nr, compare_commit_and_index_by_generation);
        min_generation = commits[0].generation;

        while (bases) {
                repo_parse_commit(r, bases->item);
                commit_list_insert(bases->item, &stack);
                bases = bases->next;
        }

        while (stack) {
                int explored_all_parents = 1;
                struct commit_list *p;
                struct commit *c = stack->item;
                timestamp_t c_gen = commit_graph_generation(c);

                /* Does it match any of our tips? */
                for (size_t j = min_generation_index; j < tips_nr; j++) {
                        if (c_gen < commits[j].generation)
                                break;

                        if (commits[j].commit == c) {
                                tips[commits[j].index]->object.flags |= mark;

                                if (j == min_generation_index) {
                                        unsigned int k = j + 1;
                                        while (k < tips_nr &&
                                               (tips[commits[k].index]->object.flags & mark))
                                                k++;

                                        /* Terminate early if all found. */
                                        if (k >= tips_nr)
                                                goto done;

                                        min_generation_index = k;
                                        min_generation = commits[k].generation;
                                }
                        }
                }

                for (p = c->parents; p; p = p->next) {
                        repo_parse_commit(r, p->item);

                        /* Have we already explored this parent? */
                        if (p->item->object.flags & SEEN)
                                continue;

                        /* Is it below the current minimum generation? */
                        if (commit_graph_generation(p->item) < min_generation)
                                continue;

                        /* Ok, we will explore from here on. */
                        p->item->object.flags |= SEEN;
                        explored_all_parents = 0;
                        commit_list_insert(p->item, &stack);
                        break;
                }

                if (explored_all_parents)
                        pop_commit(&stack);
        }

done:
        free(commits);
        repo_clear_commit_marks(r, SEEN);
}