gitlab-ci: introduce stages and dependencies

[git/gitster.git] / pack-bitmap-write.c

#define USE_THE_REPOSITORY_VARIABLE

#include "git-compat-util.h"
#include "environment.h"
#include "gettext.h"
#include "hex.h"
#include "object-store-ll.h"
#include "commit.h"
#include "diff.h"
#include "revision.h"
#include "progress.h"
#include "pack.h"
#include "pack-bitmap.h"
#include "hash-lookup.h"
#include "pack-objects.h"
#include "path.h"
#include "commit-reach.h"
#include "prio-queue.h"
#include "trace2.h"
#include "tree.h"
#include "tree-walk.h"
#include "pseudo-merge.h"
#include "oid-array.h"
#include "config.h"
#include "alloc.h"
#include "refs.h"
#include "strmap.h"

struct bitmapped_commit {
        struct commit *commit;
        struct ewah_bitmap *bitmap;
        struct ewah_bitmap *write_as;
        int flags;
        int xor_offset;
        uint32_t commit_pos;
        unsigned pseudo_merge : 1;
};

static inline int bitmap_writer_nr_selected_commits(struct bitmap_writer *writer)
{
        return writer->selected_nr - writer->pseudo_merges_nr;
}

void bitmap_writer_init(struct bitmap_writer *writer, struct repository *r,
                        struct packing_data *pdata)
{
        memset(writer, 0, sizeof(struct bitmap_writer));
        if (writer->bitmaps)
                BUG("bitmap writer already initialized");
        writer->bitmaps = kh_init_oid_map();
        writer->pseudo_merge_commits = kh_init_oid_map();
        writer->to_pack = pdata;

        string_list_init_dup(&writer->pseudo_merge_groups);

        load_pseudo_merges_from_config(r, &writer->pseudo_merge_groups);
}

static void free_pseudo_merge_commit_idx(struct pseudo_merge_commit_idx *idx)
{
        if (!idx)
                return;
        free(idx->pseudo_merge);
        free(idx);
}

void bitmap_writer_free(struct bitmap_writer *writer)
{
        uint32_t i;
        struct pseudo_merge_commit_idx *idx;

        if (!writer)
                return;

        ewah_free(writer->commits);
        ewah_free(writer->trees);
        ewah_free(writer->blobs);
        ewah_free(writer->tags);

        kh_destroy_oid_map(writer->bitmaps);

        kh_foreach_value(writer->pseudo_merge_commits, idx,
                         free_pseudo_merge_commit_idx(idx));
        kh_destroy_oid_map(writer->pseudo_merge_commits);

        for (i = 0; i < writer->selected_nr; i++) {
                struct bitmapped_commit *bc = &writer->selected[i];
                if (bc->write_as != bc->bitmap)
                        ewah_free(bc->write_as);
                ewah_free(bc->bitmap);
        }
        free(writer->selected);
}

void bitmap_writer_show_progress(struct bitmap_writer *writer, int show)
{
        writer->show_progress = show;
}

/**
 * Build the initial type index for the packfile or multi-pack-index
 */
void bitmap_writer_build_type_index(struct bitmap_writer *writer,
                                    struct pack_idx_entry **index)
{
        uint32_t i;

        writer->commits = ewah_new();
        writer->trees = ewah_new();
        writer->blobs = ewah_new();
        writer->tags = ewah_new();
        ALLOC_ARRAY(writer->to_pack->in_pack_pos, writer->to_pack->nr_objects);

        for (i = 0; i < writer->to_pack->nr_objects; ++i) {
                struct object_entry *entry = (struct object_entry *)index[i];
                enum object_type real_type;

                oe_set_in_pack_pos(writer->to_pack, entry, i);

                switch (oe_type(entry)) {
                case OBJ_COMMIT:
                case OBJ_TREE:
                case OBJ_BLOB:
                case OBJ_TAG:
                        real_type = oe_type(entry);
                        break;

                default:
                        real_type = oid_object_info(writer->to_pack->repo,
                                                    &entry->idx.oid, NULL);
                        break;
                }

                switch (real_type) {
                case OBJ_COMMIT:
                        ewah_set(writer->commits, i);
                        break;

                case OBJ_TREE:
                        ewah_set(writer->trees, i);
                        break;

                case OBJ_BLOB:
                        ewah_set(writer->blobs, i);
                        break;

                case OBJ_TAG:
                        ewah_set(writer->tags, i);
                        break;

                default:
                        die("Missing type information for %s (%d/%d)",
                            oid_to_hex(&entry->idx.oid), real_type,
                            oe_type(entry));
                }
        }
}

int bitmap_writer_has_bitmapped_object_id(struct bitmap_writer *writer,
                                          const struct object_id *oid)
{
        return kh_get_oid_map(writer->bitmaps, *oid) != kh_end(writer->bitmaps);
}

/**
 * Compute the actual bitmaps
 */

void bitmap_writer_push_commit(struct bitmap_writer *writer,
                               struct commit *commit, unsigned pseudo_merge)
{
        if (writer->selected_nr >= writer->selected_alloc) {
                writer->selected_alloc = (writer->selected_alloc + 32) * 2;
                REALLOC_ARRAY(writer->selected, writer->selected_alloc);
        }

        if (!pseudo_merge) {
                int hash_ret;
                khiter_t hash_pos = kh_put_oid_map(writer->bitmaps,
                                                   commit->object.oid,
                                                   &hash_ret);

                if (!hash_ret)
                        die(_("duplicate entry when writing bitmap index: %s"),
                            oid_to_hex(&commit->object.oid));
                kh_value(writer->bitmaps, hash_pos) = NULL;
        }

        writer->selected[writer->selected_nr].commit = commit;
        writer->selected[writer->selected_nr].bitmap = NULL;
        writer->selected[writer->selected_nr].write_as = NULL;
        writer->selected[writer->selected_nr].flags = 0;
        writer->selected[writer->selected_nr].pseudo_merge = pseudo_merge;

        writer->selected_nr++;
}

static uint32_t find_object_pos(struct bitmap_writer *writer,
                                const struct object_id *oid, int *found)
{
        struct object_entry *entry = packlist_find(writer->to_pack, oid);

        if (!entry) {
                if (found)
                        *found = 0;
                warning("Failed to write bitmap index. Packfile doesn't have full closure "
                        "(object %s is missing)", oid_to_hex(oid));
                return 0;
        }

        if (found)
                *found = 1;
        return oe_in_pack_pos(writer->to_pack, entry);
}

static void compute_xor_offsets(struct bitmap_writer *writer)
{
        static const int MAX_XOR_OFFSET_SEARCH = 10;

        int i, next = 0;

        while (next < writer->selected_nr) {
                struct bitmapped_commit *stored = &writer->selected[next];
                int best_offset = 0;
                struct ewah_bitmap *best_bitmap = stored->bitmap;
                struct ewah_bitmap *test_xor;

                if (stored->pseudo_merge)
                        goto next;

                for (i = 1; i <= MAX_XOR_OFFSET_SEARCH; ++i) {
                        int curr = next - i;

                        if (curr < 0)
                                break;
                        if (writer->selected[curr].pseudo_merge)
                                continue;

                        test_xor = ewah_pool_new();
                        ewah_xor(writer->selected[curr].bitmap, stored->bitmap, test_xor);

                        if (test_xor->buffer_size < best_bitmap->buffer_size) {
                                if (best_bitmap != stored->bitmap)
                                        ewah_pool_free(best_bitmap);

                                best_bitmap = test_xor;
                                best_offset = i;
                        } else {
                                ewah_pool_free(test_xor);
                        }
                }

next:
                stored->xor_offset = best_offset;
                stored->write_as = best_bitmap;

                next++;
        }
}

struct bb_commit {
        struct commit_list *reverse_edges;
        struct bitmap *commit_mask;
        struct bitmap *bitmap;
        unsigned selected:1,
                 maximal:1,
                 pseudo_merge:1;
        unsigned idx; /* within selected array */
};

static void clear_bb_commit(struct bb_commit *commit)
{
        free_commit_list(commit->reverse_edges);
        bitmap_free(commit->commit_mask);
        bitmap_free(commit->bitmap);
}

define_commit_slab(bb_data, struct bb_commit);

struct bitmap_builder {
        struct bb_data data;
        struct commit **commits;
        size_t commits_nr, commits_alloc;
};

static void bitmap_builder_init(struct bitmap_builder *bb,
                                struct bitmap_writer *writer,
                                struct bitmap_index *old_bitmap)
{
        struct rev_info revs;
        struct commit *commit;
        struct commit_list *reusable = NULL;
        struct commit_list *r;
        unsigned int i, num_maximal = 0;

        memset(bb, 0, sizeof(*bb));
        init_bb_data(&bb->data);

        reset_revision_walk();
        repo_init_revisions(writer->to_pack->repo, &revs, NULL);
        revs.topo_order = 1;
        revs.first_parent_only = 1;

        for (i = 0; i < writer->selected_nr; i++) {
                struct bitmapped_commit *bc = &writer->selected[i];
                struct bb_commit *ent = bb_data_at(&bb->data, bc->commit);

                ent->selected = 1;
                ent->maximal = 1;
                ent->pseudo_merge = bc->pseudo_merge;
                ent->idx = i;

                ent->commit_mask = bitmap_new();
                bitmap_set(ent->commit_mask, i);

                add_pending_object(&revs, &bc->commit->object, "");
        }

        if (prepare_revision_walk(&revs))
                die("revision walk setup failed");

        while ((commit = get_revision(&revs))) {
                struct commit_list *p = commit->parents;
                struct bb_commit *c_ent;

                parse_commit_or_die(commit);

                c_ent = bb_data_at(&bb->data, commit);

                /*
                 * If there is no commit_mask, there is no reason to iterate
                 * over this commit; it is not selected (if it were, it would
                 * not have a blank commit mask) and all its children have
                 * existing bitmaps (see the comment starting with "This commit
                 * has an existing bitmap" below), so it does not contribute
                 * anything to the final bitmap file or its descendants.
                 */
                if (!c_ent->commit_mask)
                        continue;

                if (old_bitmap && bitmap_for_commit(old_bitmap, commit)) {
                        /*
                         * This commit has an existing bitmap, so we can
                         * get its bits immediately without an object
                         * walk. That is, it is reusable as-is and there is no
                         * need to continue walking beyond it.
                         *
                         * Mark it as such and add it to bb->commits separately
                         * to avoid allocating a position in the commit mask.
                         */
                        commit_list_insert(commit, &reusable);
                        goto next;
                }

                if (c_ent->maximal) {
                        num_maximal++;
                        ALLOC_GROW(bb->commits, bb->commits_nr + 1, bb->commits_alloc);
                        bb->commits[bb->commits_nr++] = commit;
                }

                if (p) {
                        struct bb_commit *p_ent = bb_data_at(&bb->data, p->item);
                        int c_not_p, p_not_c;

                        if (!p_ent->commit_mask) {
                                p_ent->commit_mask = bitmap_new();
                                c_not_p = 1;
                                p_not_c = 0;
                        } else {
                                c_not_p = bitmap_is_subset(c_ent->commit_mask, p_ent->commit_mask);
                                p_not_c = bitmap_is_subset(p_ent->commit_mask, c_ent->commit_mask);
                        }

                        if (!c_not_p)
                                continue;

                        bitmap_or(p_ent->commit_mask, c_ent->commit_mask);

                        if (p_not_c)
                                p_ent->maximal = 1;
                        else {
                                p_ent->maximal = 0;
                                free_commit_list(p_ent->reverse_edges);
                                p_ent->reverse_edges = NULL;
                        }

                        if (c_ent->maximal) {
                                commit_list_insert(commit, &p_ent->reverse_edges);
                        } else {
                                struct commit_list *cc = c_ent->reverse_edges;

                                for (; cc; cc = cc->next) {
                                        if (!commit_list_contains(cc->item, p_ent->reverse_edges))
                                                commit_list_insert(cc->item, &p_ent->reverse_edges);
                                }
                        }
                }

next:
                bitmap_free(c_ent->commit_mask);
                c_ent->commit_mask = NULL;
        }

        for (r = reusable; r; r = r->next) {
                ALLOC_GROW(bb->commits, bb->commits_nr + 1, bb->commits_alloc);
                bb->commits[bb->commits_nr++] = r->item;
        }

        trace2_data_intmax("pack-bitmap-write", the_repository,
                           "num_selected_commits", writer->selected_nr);
        trace2_data_intmax("pack-bitmap-write", the_repository,
                           "num_maximal_commits", num_maximal);

        release_revisions(&revs);
        free_commit_list(reusable);
}

static void bitmap_builder_clear(struct bitmap_builder *bb)
{
        deep_clear_bb_data(&bb->data, clear_bb_commit);
        free(bb->commits);
        bb->commits_nr = bb->commits_alloc = 0;
}

static int fill_bitmap_tree(struct bitmap_writer *writer,
                            struct bitmap *bitmap,
                            struct tree *tree)
{
        int found;
        uint32_t pos;
        struct tree_desc desc;
        struct name_entry entry;

        /*
         * If our bit is already set, then there is nothing to do. Both this
         * tree and all of its children will be set.
         */
        pos = find_object_pos(writer, &tree->object.oid, &found);
        if (!found)
                return -1;
        if (bitmap_get(bitmap, pos))
                return 0;
        bitmap_set(bitmap, pos);

        if (parse_tree(tree) < 0)
                die("unable to load tree object %s",
                    oid_to_hex(&tree->object.oid));
        init_tree_desc(&desc, &tree->object.oid, tree->buffer, tree->size);

        while (tree_entry(&desc, &entry)) {
                switch (object_type(entry.mode)) {
                case OBJ_TREE:
                        if (fill_bitmap_tree(writer, bitmap,
                                             lookup_tree(the_repository, &entry.oid)) < 0)
                                return -1;
                        break;
                case OBJ_BLOB:
                        pos = find_object_pos(writer, &entry.oid, &found);
                        if (!found)
                                return -1;
                        bitmap_set(bitmap, pos);
                        break;
                default:
                        /* Gitlink, etc; not reachable */
                        break;
                }
        }

        free_tree_buffer(tree);
        return 0;
}

static int reused_bitmaps_nr;
static int reused_pseudo_merge_bitmaps_nr;

static int fill_bitmap_commit(struct bitmap_writer *writer,
                              struct bb_commit *ent,
                              struct commit *commit,
                              struct prio_queue *queue,
                              struct prio_queue *tree_queue,
                              struct bitmap_index *old_bitmap,
                              const uint32_t *mapping)
{
        int found;
        uint32_t pos;
        if (!ent->bitmap)
                ent->bitmap = bitmap_new();

        prio_queue_put(queue, commit);

        while (queue->nr) {
                struct commit_list *p;
                struct commit *c = prio_queue_get(queue);

                if (old_bitmap && mapping) {
                        struct ewah_bitmap *old;
                        struct bitmap *remapped = bitmap_new();

                        if (commit->object.flags & BITMAP_PSEUDO_MERGE)
                                old = pseudo_merge_bitmap_for_commit(old_bitmap, c);
                        else
                                old = bitmap_for_commit(old_bitmap, c);
                        /*
                         * If this commit has an old bitmap, then translate that
                         * bitmap and add its bits to this one. No need to walk
                         * parents or the tree for this commit.
                         */
                        if (old && !rebuild_bitmap(mapping, old, remapped)) {
                                bitmap_or(ent->bitmap, remapped);
                                bitmap_free(remapped);
                                if (commit->object.flags & BITMAP_PSEUDO_MERGE)
                                        reused_pseudo_merge_bitmaps_nr++;
                                else
                                        reused_bitmaps_nr++;
                                continue;
                        }
                        bitmap_free(remapped);
                }

                /*
                 * Mark ourselves and queue our tree. The commit
                 * walk ensures we cover all parents.
                 */
                if (!(c->object.flags & BITMAP_PSEUDO_MERGE)) {
                        pos = find_object_pos(writer, &c->object.oid, &found);
                        if (!found)
                                return -1;
                        bitmap_set(ent->bitmap, pos);
                        prio_queue_put(tree_queue,
                                       repo_get_commit_tree(the_repository, c));
                }

                for (p = c->parents; p; p = p->next) {
                        pos = find_object_pos(writer, &p->item->object.oid,
                                              &found);
                        if (!found)
                                return -1;
                        if (!bitmap_get(ent->bitmap, pos)) {
                                bitmap_set(ent->bitmap, pos);
                                prio_queue_put(queue, p->item);
                        }
                }
        }

        while (tree_queue->nr) {
                if (fill_bitmap_tree(writer, ent->bitmap,
                                     prio_queue_get(tree_queue)) < 0)
                        return -1;
        }
        return 0;
}

static void store_selected(struct bitmap_writer *writer,
                           struct bb_commit *ent, struct commit *commit)
{
        struct bitmapped_commit *stored = &writer->selected[ent->idx];
        khiter_t hash_pos;

        stored->bitmap = bitmap_to_ewah(ent->bitmap);

        if (ent->pseudo_merge)
                return;

        hash_pos = kh_get_oid_map(writer->bitmaps, commit->object.oid);
        if (hash_pos == kh_end(writer->bitmaps))
                die(_("attempted to store non-selected commit: '%s'"),
                    oid_to_hex(&commit->object.oid));

        kh_value(writer->bitmaps, hash_pos) = stored;
}

int bitmap_writer_build(struct bitmap_writer *writer)
{
        struct bitmap_builder bb;
        size_t i;
        int nr_stored = 0; /* for progress */
        struct prio_queue queue = { compare_commits_by_gen_then_commit_date };
        struct prio_queue tree_queue = { NULL };
        struct bitmap_index *old_bitmap;
        uint32_t *mapping;
        int closed = 1; /* until proven otherwise */

        if (writer->show_progress)
                writer->progress = start_progress("Building bitmaps",
                                                  writer->selected_nr);
        trace2_region_enter("pack-bitmap-write", "building_bitmaps_total",
                            the_repository);

        old_bitmap = prepare_bitmap_git(writer->to_pack->repo);
        if (old_bitmap)
                mapping = create_bitmap_mapping(old_bitmap, writer->to_pack);
        else
                mapping = NULL;

        bitmap_builder_init(&bb, writer, old_bitmap);
        for (i = bb.commits_nr; i > 0; i--) {
                struct commit *commit = bb.commits[i-1];
                struct bb_commit *ent = bb_data_at(&bb.data, commit);
                struct commit *child;
                int reused = 0;

                if (fill_bitmap_commit(writer, ent, commit, &queue, &tree_queue,
                                       old_bitmap, mapping) < 0) {
                        closed = 0;
                        break;
                }

                if (ent->selected) {
                        store_selected(writer, ent, commit);
                        nr_stored++;
                        display_progress(writer->progress, nr_stored);
                }

                while ((child = pop_commit(&ent->reverse_edges))) {
                        struct bb_commit *child_ent =
                                bb_data_at(&bb.data, child);

                        if (child_ent->bitmap)
                                bitmap_or(child_ent->bitmap, ent->bitmap);
                        else if (reused)
                                child_ent->bitmap = bitmap_dup(ent->bitmap);
                        else {
                                child_ent->bitmap = ent->bitmap;
                                reused = 1;
                        }
                }
                if (!reused)
                        bitmap_free(ent->bitmap);
                ent->bitmap = NULL;
        }
        clear_prio_queue(&queue);
        clear_prio_queue(&tree_queue);
        bitmap_builder_clear(&bb);
        free_bitmap_index(old_bitmap);
        free(mapping);

        trace2_region_leave("pack-bitmap-write", "building_bitmaps_total",
                            the_repository);
        trace2_data_intmax("pack-bitmap-write", the_repository,
                           "building_bitmaps_reused", reused_bitmaps_nr);
        trace2_data_intmax("pack-bitmap-write", the_repository,
                           "building_bitmaps_pseudo_merge_reused",
                           reused_pseudo_merge_bitmaps_nr);

        stop_progress(&writer->progress);

        if (closed)
                compute_xor_offsets(writer);
        return closed ? 0 : -1;
}

/**
 * Select the commits that will be bitmapped
 */
static inline unsigned int next_commit_index(unsigned int idx)
{
        static const unsigned int MIN_COMMITS = 100;
        static const unsigned int MAX_COMMITS = 5000;

        static const unsigned int MUST_REGION = 100;
        static const unsigned int MIN_REGION = 20000;

        unsigned int offset, next;

        if (idx <= MUST_REGION)
                return 0;

        if (idx <= MIN_REGION) {
                offset = idx - MUST_REGION;
                return (offset < MIN_COMMITS) ? offset : MIN_COMMITS;
        }

        offset = idx - MIN_REGION;
        next = (offset < MAX_COMMITS) ? offset : MAX_COMMITS;

        return (next > MIN_COMMITS) ? next : MIN_COMMITS;
}

static int date_compare(const void *_a, const void *_b)
{
        struct commit *a = *(struct commit **)_a;
        struct commit *b = *(struct commit **)_b;
        return (long)b->date - (long)a->date;
}

void bitmap_writer_select_commits(struct bitmap_writer *writer,
                                  struct commit **indexed_commits,
                                  unsigned int indexed_commits_nr)
{
        unsigned int i = 0, j, next;

        QSORT(indexed_commits, indexed_commits_nr, date_compare);

        if (indexed_commits_nr < 100) {
                for (i = 0; i < indexed_commits_nr; ++i)
                        bitmap_writer_push_commit(writer, indexed_commits[i], 0);

                select_pseudo_merges(writer);

                return;
        }

        if (writer->show_progress)
                writer->progress = start_progress("Selecting bitmap commits", 0);

        for (;;) {
                struct commit *chosen = NULL;

                next = next_commit_index(i);

                if (i + next >= indexed_commits_nr)
                        break;

                if (next == 0) {
                        chosen = indexed_commits[i];
                } else {
                        chosen = indexed_commits[i + next];

                        for (j = 0; j <= next; ++j) {
                                struct commit *cm = indexed_commits[i + j];

                                if ((cm->object.flags & NEEDS_BITMAP) != 0) {
                                        chosen = cm;
                                        break;
                                }

                                if (cm->parents && cm->parents->next)
                                        chosen = cm;
                        }
                }

                bitmap_writer_push_commit(writer, chosen, 0);

                i += next + 1;
                display_progress(writer->progress, i);
        }

        stop_progress(&writer->progress);

        select_pseudo_merges(writer);
}


static int hashwrite_ewah_helper(void *f, const void *buf, size_t len)
{
        /* hashwrite will die on error */
        hashwrite(f, buf, len);
        return len;
}

/**
 * Write the bitmap index to disk
 */
static inline void dump_bitmap(struct hashfile *f, struct ewah_bitmap *bitmap)
{
        if (ewah_serialize_to(bitmap, hashwrite_ewah_helper, f) < 0)
                die("Failed to write bitmap index");
}

static const struct object_id *oid_access(size_t pos, const void *table)
{
        const struct pack_idx_entry * const *index = table;
        return &index[pos]->oid;
}

static void write_selected_commits_v1(struct bitmap_writer *writer,
                                      struct hashfile *f, off_t *offsets)
{
        int i;

        for (i = 0; i < bitmap_writer_nr_selected_commits(writer); ++i) {
                struct bitmapped_commit *stored = &writer->selected[i];
                if (stored->pseudo_merge)
                        BUG("unexpected pseudo-merge among selected: %s",
                            oid_to_hex(&stored->commit->object.oid));

                if (offsets)
                        offsets[i] = hashfile_total(f);

                hashwrite_be32(f, stored->commit_pos);
                hashwrite_u8(f, stored->xor_offset);
                hashwrite_u8(f, stored->flags);

                dump_bitmap(f, stored->write_as);
        }
}

static void write_pseudo_merges(struct bitmap_writer *writer,
                                struct hashfile *f)
{
        struct oid_array commits = OID_ARRAY_INIT;
        struct bitmap **commits_bitmap = NULL;
        off_t *pseudo_merge_ofs = NULL;
        off_t start, table_start, next_ext;

        uint32_t base = bitmap_writer_nr_selected_commits(writer);
        size_t i, j = 0;

        CALLOC_ARRAY(commits_bitmap, writer->pseudo_merges_nr);
        CALLOC_ARRAY(pseudo_merge_ofs, writer->pseudo_merges_nr);

        for (i = 0; i < writer->pseudo_merges_nr; i++) {
                struct bitmapped_commit *merge = &writer->selected[base + i];
                struct commit_list *p;

                if (!merge->pseudo_merge)
                        BUG("found non-pseudo merge commit at %"PRIuMAX, (uintmax_t)i);

                commits_bitmap[i] = bitmap_new();

                for (p = merge->commit->parents; p; p = p->next)
                        bitmap_set(commits_bitmap[i],
                                   find_object_pos(writer, &p->item->object.oid,
                                                   NULL));
        }

        start = hashfile_total(f);

        for (i = 0; i < writer->pseudo_merges_nr; i++) {
                struct ewah_bitmap *commits_ewah = bitmap_to_ewah(commits_bitmap[i]);

                pseudo_merge_ofs[i] = hashfile_total(f);

                dump_bitmap(f, commits_ewah);
                dump_bitmap(f, writer->selected[base+i].write_as);

                ewah_free(commits_ewah);
        }

        next_ext = st_add(hashfile_total(f),
                          st_mult(kh_size(writer->pseudo_merge_commits),
                                  sizeof(uint64_t)));

        table_start = hashfile_total(f);

        commits.alloc = kh_size(writer->pseudo_merge_commits);
        CALLOC_ARRAY(commits.oid, commits.alloc);

        for (i = kh_begin(writer->pseudo_merge_commits); i != kh_end(writer->pseudo_merge_commits); i++) {
                if (!kh_exist(writer->pseudo_merge_commits, i))
                        continue;
                oid_array_append(&commits, &kh_key(writer->pseudo_merge_commits, i));
        }

        oid_array_sort(&commits);

        /* write lookup table (non-extended) */
        for (i = 0; i < commits.nr; i++) {
                int hash_pos;
                struct pseudo_merge_commit_idx *c;

                hash_pos = kh_get_oid_map(writer->pseudo_merge_commits,
                                          commits.oid[i]);
                if (hash_pos == kh_end(writer->pseudo_merge_commits))
                        BUG("could not find pseudo-merge commit %s",
                            oid_to_hex(&commits.oid[i]));

                c = kh_value(writer->pseudo_merge_commits, hash_pos);

                hashwrite_be32(f, find_object_pos(writer, &commits.oid[i],
                                                  NULL));
                if (c->nr == 1)
                        hashwrite_be64(f, pseudo_merge_ofs[c->pseudo_merge[0]]);
                else if (c->nr > 1) {
                        if (next_ext & ((uint64_t)1<<63))
                                die(_("too many pseudo-merges"));
                        hashwrite_be64(f, next_ext | ((uint64_t)1<<63));
                        next_ext = st_add3(next_ext,
                                           sizeof(uint32_t),
                                           st_mult(c->nr, sizeof(uint64_t)));
                } else
                        BUG("expected commit '%s' to have at least one "
                            "pseudo-merge", oid_to_hex(&commits.oid[i]));
        }

        /* write lookup table (extended) */
        for (i = 0; i < commits.nr; i++) {
                int hash_pos;
                struct pseudo_merge_commit_idx *c;

                hash_pos = kh_get_oid_map(writer->pseudo_merge_commits,
                                          commits.oid[i]);
                if (hash_pos == kh_end(writer->pseudo_merge_commits))
                        BUG("could not find pseudo-merge commit %s",
                            oid_to_hex(&commits.oid[i]));

                c = kh_value(writer->pseudo_merge_commits, hash_pos);
                if (c->nr == 1)
                        continue;

                hashwrite_be32(f, c->nr);
                for (j = 0; j < c->nr; j++)
                        hashwrite_be64(f, pseudo_merge_ofs[c->pseudo_merge[j]]);
        }

        /* write positions for all pseudo merges */
        for (i = 0; i < writer->pseudo_merges_nr; i++)
                hashwrite_be64(f, pseudo_merge_ofs[i]);

        hashwrite_be32(f, writer->pseudo_merges_nr);
        hashwrite_be32(f, kh_size(writer->pseudo_merge_commits));
        hashwrite_be64(f, table_start - start);
        hashwrite_be64(f, hashfile_total(f) - start + sizeof(uint64_t));

        for (i = 0; i < writer->pseudo_merges_nr; i++)
                bitmap_free(commits_bitmap[i]);

        free(pseudo_merge_ofs);
        free(commits_bitmap);
}

static int table_cmp(const void *_va, const void *_vb, void *_data)
{
        struct bitmap_writer *writer = _data;
        struct bitmapped_commit *a = &writer->selected[*(uint32_t *)_va];
        struct bitmapped_commit *b = &writer->selected[*(uint32_t *)_vb];

        if (a->commit_pos < b->commit_pos)
                return -1;
        else if (a->commit_pos > b->commit_pos)
                return 1;

        return 0;
}

static void write_lookup_table(struct bitmap_writer *writer, struct hashfile *f,
                               off_t *offsets)
{
        uint32_t i;
        uint32_t *table, *table_inv;

        ALLOC_ARRAY(table, bitmap_writer_nr_selected_commits(writer));
        ALLOC_ARRAY(table_inv, bitmap_writer_nr_selected_commits(writer));

        for (i = 0; i < bitmap_writer_nr_selected_commits(writer); i++)
                table[i] = i;

        /*
         * At the end of this sort table[j] = i means that the i'th
         * bitmap corresponds to j'th bitmapped commit (among the selected
         * commits) in lex order of OIDs.
         */
        QSORT_S(table, bitmap_writer_nr_selected_commits(writer), table_cmp, writer);

        /* table_inv helps us discover that relationship (i'th bitmap
         * to j'th commit by j = table_inv[i])
         */
        for (i = 0; i < bitmap_writer_nr_selected_commits(writer); i++)
                table_inv[table[i]] = i;

        trace2_region_enter("pack-bitmap-write", "writing_lookup_table", the_repository);
        for (i = 0; i < bitmap_writer_nr_selected_commits(writer); i++) {
                struct bitmapped_commit *selected = &writer->selected[table[i]];
                uint32_t xor_offset = selected->xor_offset;
                uint32_t xor_row;

                if (xor_offset) {
                        /*
                         * xor_index stores the index (in the bitmap entries)
                         * of the corresponding xor bitmap. But we need to convert
                         * this index into lookup table's index. So, table_inv[xor_index]
                         * gives us the index position w.r.t. the lookup table.
                         *
                         * If "k = table[i] - xor_offset" then the xor base is the k'th
                         * bitmap. `table_inv[k]` gives us the position of that bitmap
                         * in the lookup table.
                         */
                        uint32_t xor_index = table[i] - xor_offset;
                        xor_row = table_inv[xor_index];
                } else {
                        xor_row = 0xffffffff;
                }

                hashwrite_be32(f, writer->selected[table[i]].commit_pos);
                hashwrite_be64(f, (uint64_t)offsets[table[i]]);
                hashwrite_be32(f, xor_row);
        }
        trace2_region_leave("pack-bitmap-write", "writing_lookup_table", the_repository);

        free(table);
        free(table_inv);
}

static void write_hash_cache(struct hashfile *f,
                             struct pack_idx_entry **index,
                             uint32_t index_nr)
{
        uint32_t i;

        for (i = 0; i < index_nr; ++i) {
                struct object_entry *entry = (struct object_entry *)index[i];
                hashwrite_be32(f, entry->hash);
        }
}

void bitmap_writer_set_checksum(struct bitmap_writer *writer,
                                const unsigned char *sha1)
{
        hashcpy(writer->pack_checksum, sha1, the_repository->hash_algo);
}

void bitmap_writer_finish(struct bitmap_writer *writer,
                          struct pack_idx_entry **index,
                          const char *filename,
                          uint16_t options)
{
        static uint16_t default_version = 1;
        static uint16_t flags = BITMAP_OPT_FULL_DAG;
        struct strbuf tmp_file = STRBUF_INIT;
        struct hashfile *f;
        off_t *offsets = NULL;
        uint32_t i;

        struct bitmap_disk_header header;

        int fd = odb_mkstemp(&tmp_file, "pack/tmp_bitmap_XXXXXX");

        if (writer->pseudo_merges_nr)
                options |= BITMAP_OPT_PSEUDO_MERGES;

        f = hashfd(fd, tmp_file.buf);

        memcpy(header.magic, BITMAP_IDX_SIGNATURE, sizeof(BITMAP_IDX_SIGNATURE));
        header.version = htons(default_version);
        header.options = htons(flags | options);
        header.entry_count = htonl(bitmap_writer_nr_selected_commits(writer));
        hashcpy(header.checksum, writer->pack_checksum, the_repository->hash_algo);

        hashwrite(f, &header, sizeof(header) - GIT_MAX_RAWSZ + the_hash_algo->rawsz);
        dump_bitmap(f, writer->commits);
        dump_bitmap(f, writer->trees);
        dump_bitmap(f, writer->blobs);
        dump_bitmap(f, writer->tags);

        if (options & BITMAP_OPT_LOOKUP_TABLE)
                CALLOC_ARRAY(offsets, writer->to_pack->nr_objects);

        for (i = 0; i < bitmap_writer_nr_selected_commits(writer); i++) {
                struct bitmapped_commit *stored = &writer->selected[i];
                int commit_pos = oid_pos(&stored->commit->object.oid, index,
                                         writer->to_pack->nr_objects,
                                         oid_access);

                if (commit_pos < 0)
                        BUG(_("trying to write commit not in index"));
                stored->commit_pos = commit_pos;
        }

        write_selected_commits_v1(writer, f, offsets);

        if (options & BITMAP_OPT_PSEUDO_MERGES)
                write_pseudo_merges(writer, f);

        if (options & BITMAP_OPT_LOOKUP_TABLE)
                write_lookup_table(writer, f, offsets);

        if (options & BITMAP_OPT_HASH_CACHE)
                write_hash_cache(f, index, writer->to_pack->nr_objects);

        finalize_hashfile(f, NULL, FSYNC_COMPONENT_PACK_METADATA,
                          CSUM_HASH_IN_STREAM | CSUM_FSYNC | CSUM_CLOSE);

        if (adjust_shared_perm(tmp_file.buf))
                die_errno("unable to make temporary bitmap file readable");

        if (rename(tmp_file.buf, filename))
                die_errno("unable to rename temporary bitmap file to '%s'", filename);

        strbuf_release(&tmp_file);
        free(offsets);
}