+#include "cache.h"
+#include "commit.h"
+#include "tag.h"
+#include "diff.h"
+#include "revision.h"
+#include "progress.h"
+#include "list-objects.h"
+#include "pack.h"
+#include "pack-bitmap.h"
+#include "pack-revindex.h"
+#include "pack-objects.h"
+
+/*
+ * An entry on the bitmap index, representing the bitmap for a given
+ * commit.
+ */
+struct stored_bitmap {
+       unsigned char sha1[20];
+       struct ewah_bitmap *root;
+       struct stored_bitmap *xor;
+       int flags;
+};
+
+/*
+ * The currently active bitmap index. By design, repositories only have
+ * a single bitmap index available (the index for the biggest packfile in
+ * the repository), since bitmap indexes need full closure.
+ *
+ * If there is more than one bitmap index available (e.g. because of alternates),
+ * the active bitmap index is the largest one.
+ */
+static struct bitmap_index {
+       /* Packfile to which this bitmap index belongs to */
+       struct packed_git *pack;
+
+       /* reverse index for the packfile */
+       struct pack_revindex *reverse_index;
+
+       /*
+        * Mark the first `reuse_objects` in the packfile as reused:
+        * they will be sent as-is without using them for repacking
+        * calculations
+        */
+       uint32_t reuse_objects;
+
+       /* mmapped buffer of the whole bitmap index */
+       unsigned char *map;
+       size_t map_size; /* size of the mmaped buffer */
+       size_t map_pos; /* current position when loading the index */
+
+       /*
+        * Type indexes.
+        *
+        * Each bitmap marks which objects in the packfile  are of the given
+        * type. This provides type information when yielding the objects from
+        * the packfile during a walk, which allows for better delta bases.
+        */
+       struct ewah_bitmap *commits;
+       struct ewah_bitmap *trees;
+       struct ewah_bitmap *blobs;
+       struct ewah_bitmap *tags;
+
+       /* Map from SHA1 -> `stored_bitmap` for all the bitmapped comits */
+       khash_sha1 *bitmaps;
+
+       /* Number of bitmapped commits */
+       uint32_t entry_count;
+
+       /*
+        * Extended index.
+        *
+        * When trying to perform bitmap operations with objects that are not
+        * packed in `pack`, these objects are added to this "fake index" and
+        * are assumed to appear at the end of the packfile for all operations
+        */
+       struct eindex {
+               struct object **objects;
+               uint32_t *hashes;
+               uint32_t count, alloc;
+               khash_sha1_pos *positions;
+       } ext_index;
+
+       /* Bitmap result of the last performed walk */
+       struct bitmap *result;
+
+       /* Version of the bitmap index */
+       unsigned int version;
+
+       unsigned loaded : 1;
+
+} bitmap_git;
+
+static struct ewah_bitmap *lookup_stored_bitmap(struct stored_bitmap *st)
+{
+       struct ewah_bitmap *parent;
+       struct ewah_bitmap *composed;
+
+       if (st->xor == NULL)
+               return st->root;
+
+       composed = ewah_pool_new();
+       parent = lookup_stored_bitmap(st->xor);
+       ewah_xor(st->root, parent, composed);
+
+       ewah_pool_free(st->root);
+       st->root = composed;
+       st->xor = NULL;
+
+       return composed;
+}
+
+/*
+ * Read a bitmap from the current read position on the mmaped
+ * index, and increase the read position accordingly
+ */
+static struct ewah_bitmap *read_bitmap_1(struct bitmap_index *index)
+{
+       struct ewah_bitmap *b = ewah_pool_new();
+
+       int bitmap_size = ewah_read_mmap(b,
+               index->map + index->map_pos,
+               index->map_size - index->map_pos);
+
+       if (bitmap_size < 0) {
+               error("Failed to load bitmap index (corrupted?)");
+               ewah_pool_free(b);
+               return NULL;
+       }
+
+       index->map_pos += bitmap_size;
+       return b;
+}
+
+static int load_bitmap_header(struct bitmap_index *index)
+{
+       struct bitmap_disk_header *header = (void *)index->map;
+
+       if (index->map_size < sizeof(*header) + 20)
+               return error("Corrupted bitmap index (missing header data)");
+
+       if (memcmp(header->magic, BITMAP_IDX_SIGNATURE, sizeof(BITMAP_IDX_SIGNATURE)) != 0)
+               return error("Corrupted bitmap index file (wrong header)");
+
+       index->version = ntohs(header->version);
+       if (index->version != 1)
+               return error("Unsupported version for bitmap index file (%d)", index->version);
+
+       /* Parse known bitmap format options */
+       {
+               uint32_t flags = ntohs(header->options);
+
+               if ((flags & BITMAP_OPT_FULL_DAG) == 0)
+                       return error("Unsupported options for bitmap index file "
+                               "(Git requires BITMAP_OPT_FULL_DAG)");
+       }
+
+       index->entry_count = ntohl(header->entry_count);
+       index->map_pos += sizeof(*header);
+       return 0;
+}
+
+static struct stored_bitmap *store_bitmap(struct bitmap_index *index,
+                                         struct ewah_bitmap *root,
+                                         const unsigned char *sha1,
+                                         struct stored_bitmap *xor_with,
+                                         int flags)
+{
+       struct stored_bitmap *stored;
+       khiter_t hash_pos;
+       int ret;
+
+       stored = xmalloc(sizeof(struct stored_bitmap));
+       stored->root = root;
+       stored->xor = xor_with;
+       stored->flags = flags;
+       hashcpy(stored->sha1, sha1);
+
+       hash_pos = kh_put_sha1(index->bitmaps, stored->sha1, &ret);
+
+       /* a 0 return code means the insertion succeeded with no changes,
+        * because the SHA1 already existed on the map. this is bad, there
+        * shouldn't be duplicated commits in the index */
+       if (ret == 0) {
+               error("Duplicate entry in bitmap index: %s", sha1_to_hex(sha1));
+               return NULL;
+       }
+
+       kh_value(index->bitmaps, hash_pos) = stored;
+       return stored;
+}
+
+static int load_bitmap_entries_v1(struct bitmap_index *index)
+{
+       static const size_t MAX_XOR_OFFSET = 160;
+
+       uint32_t i;
+       struct stored_bitmap **recent_bitmaps;
+       struct bitmap_disk_entry *entry;
+
+       recent_bitmaps = xcalloc(MAX_XOR_OFFSET, sizeof(struct stored_bitmap));
+
+       for (i = 0; i < index->entry_count; ++i) {
+               int xor_offset, flags;
+               struct ewah_bitmap *bitmap = NULL;
+               struct stored_bitmap *xor_bitmap = NULL;
+               uint32_t commit_idx_pos;
+               const unsigned char *sha1;
+
+               entry = (struct bitmap_disk_entry *)(index->map + index->map_pos);
+               index->map_pos += sizeof(struct bitmap_disk_entry);
+
+               commit_idx_pos = ntohl(entry->object_pos);
+               sha1 = nth_packed_object_sha1(index->pack, commit_idx_pos);
+
+               xor_offset = (int)entry->xor_offset;
+               flags = (int)entry->flags;
+
+               bitmap = read_bitmap_1(index);
+               if (!bitmap)
+                       return -1;
+
+               if (xor_offset > MAX_XOR_OFFSET || xor_offset > i)
+                       return error("Corrupted bitmap pack index");
+
+               if (xor_offset > 0) {
+                       xor_bitmap = recent_bitmaps[(i - xor_offset) % MAX_XOR_OFFSET];
+
+                       if (xor_bitmap == NULL)
+                               return error("Invalid XOR offset in bitmap pack index");
+               }
+
+               recent_bitmaps[i % MAX_XOR_OFFSET] = store_bitmap(
+                       index, bitmap, sha1, xor_bitmap, flags);
+       }
+
+       return 0;
+}
+
+static int open_pack_bitmap_1(struct packed_git *packfile)
+{
+       int fd;
+       struct stat st;
+       char *idx_name;
+
+       if (open_pack_index(packfile))
+               return -1;
+
+       idx_name = pack_bitmap_filename(packfile);
+       fd = git_open_noatime(idx_name);
+       free(idx_name);
+
+       if (fd < 0)
+               return -1;
+
+       if (fstat(fd, &st)) {
+               close(fd);
+               return -1;
+       }
+
+       if (bitmap_git.pack) {
+               warning("ignoring extra bitmap file: %s", packfile->pack_name);
+               close(fd);
+               return -1;
+       }
+
+       bitmap_git.pack = packfile;
+       bitmap_git.map_size = xsize_t(st.st_size);
+       bitmap_git.map = xmmap(NULL, bitmap_git.map_size, PROT_READ, MAP_PRIVATE, fd, 0);
+       bitmap_git.map_pos = 0;
+       close(fd);
+
+       if (load_bitmap_header(&bitmap_git) < 0) {
+               munmap(bitmap_git.map, bitmap_git.map_size);
+               bitmap_git.map = NULL;
+               bitmap_git.map_size = 0;
+               return -1;
+       }
+
+       return 0;
+}
+
+static int load_pack_bitmap(void)
+{
+       assert(bitmap_git.map && !bitmap_git.loaded);
+
+       bitmap_git.bitmaps = kh_init_sha1();
+       bitmap_git.ext_index.positions = kh_init_sha1_pos();
+       bitmap_git.reverse_index = revindex_for_pack(bitmap_git.pack);
+
+       if (!(bitmap_git.commits = read_bitmap_1(&bitmap_git)) ||
+               !(bitmap_git.trees = read_bitmap_1(&bitmap_git)) ||
+               !(bitmap_git.blobs = read_bitmap_1(&bitmap_git)) ||
+               !(bitmap_git.tags = read_bitmap_1(&bitmap_git)))
+               goto failed;
+
+       if (load_bitmap_entries_v1(&bitmap_git) < 0)
+               goto failed;
+
+       bitmap_git.loaded = 1;
+       return 0;
+
+failed:
+       munmap(bitmap_git.map, bitmap_git.map_size);
+       bitmap_git.map = NULL;
+       bitmap_git.map_size = 0;
+       return -1;
+}
+
+char *pack_bitmap_filename(struct packed_git *p)
+{
+       char *idx_name;
+       int len;
+
+       len = strlen(p->pack_name) - strlen(".pack");
+       idx_name = xmalloc(len + strlen(".bitmap") + 1);
+
+       memcpy(idx_name, p->pack_name, len);
+       memcpy(idx_name + len, ".bitmap", strlen(".bitmap") + 1);
+
+       return idx_name;
+}
+
+static int open_pack_bitmap(void)
+{
+       struct packed_git *p;
+       int ret = -1;
+
+       assert(!bitmap_git.map && !bitmap_git.loaded);
+
+       prepare_packed_git();
+       for (p = packed_git; p; p = p->next) {
+               if (open_pack_bitmap_1(p) == 0)
+                       ret = 0;
+       }
+
+       return ret;
+}
+
+int prepare_bitmap_git(void)
+{
+       if (bitmap_git.loaded)
+               return 0;
+
+       if (!open_pack_bitmap())
+               return load_pack_bitmap();
+
+       return -1;
+}
+
+struct include_data {
+       struct bitmap *base;
+       struct bitmap *seen;
+};
+
+static inline int bitmap_position_extended(const unsigned char *sha1)
+{
+       khash_sha1_pos *positions = bitmap_git.ext_index.positions;
+       khiter_t pos = kh_get_sha1_pos(positions, sha1);
+
+       if (pos < kh_end(positions)) {
+               int bitmap_pos = kh_value(positions, pos);
+               return bitmap_pos + bitmap_git.pack->num_objects;
+       }
+
+       return -1;
+}
+
+static inline int bitmap_position_packfile(const unsigned char *sha1)
+{
+       off_t offset = find_pack_entry_one(sha1, bitmap_git.pack);
+       if (!offset)
+               return -1;
+
+       return find_revindex_position(bitmap_git.reverse_index, offset);
+}
+
+static int bitmap_position(const unsigned char *sha1)
+{
+       int pos = bitmap_position_packfile(sha1);
+       return (pos >= 0) ? pos : bitmap_position_extended(sha1);
+}
+
+static int ext_index_add_object(struct object *object, const char *name)
+{
+       struct eindex *eindex = &bitmap_git.ext_index;
+
+       khiter_t hash_pos;
+       int hash_ret;
+       int bitmap_pos;
+
+       hash_pos = kh_put_sha1_pos(eindex->positions, object->sha1, &hash_ret);
+       if (hash_ret > 0) {
+               if (eindex->count >= eindex->alloc) {
+                       eindex->alloc = (eindex->alloc + 16) * 3 / 2;
+                       eindex->objects = xrealloc(eindex->objects,
+                               eindex->alloc * sizeof(struct object *));
+                       eindex->hashes = xrealloc(eindex->hashes,
+                               eindex->alloc * sizeof(uint32_t));
+               }
+
+               bitmap_pos = eindex->count;
+               eindex->objects[eindex->count] = object;
+               eindex->hashes[eindex->count] = pack_name_hash(name);
+               kh_value(eindex->positions, hash_pos) = bitmap_pos;
+               eindex->count++;
+       } else {
+               bitmap_pos = kh_value(eindex->positions, hash_pos);
+       }
+
+       return bitmap_pos + bitmap_git.pack->num_objects;
+}
+
+static void show_object(struct object *object, const struct name_path *path,
+                       const char *last, void *data)
+{
+       struct bitmap *base = data;
+       int bitmap_pos;
+
+       bitmap_pos = bitmap_position(object->sha1);
+
+       if (bitmap_pos < 0) {
+               char *name = path_name(path, last);
+               bitmap_pos = ext_index_add_object(object, name);
+               free(name);
+       }
+
+       bitmap_set(base, bitmap_pos);
+}
+
+static void show_commit(struct commit *commit, void *data)
+{
+}
+
+static int add_to_include_set(struct include_data *data,
+                             const unsigned char *sha1,
+                             int bitmap_pos)
+{
+       khiter_t hash_pos;
+
+       if (data->seen && bitmap_get(data->seen, bitmap_pos))
+               return 0;
+
+       if (bitmap_get(data->base, bitmap_pos))
+               return 0;
+
+       hash_pos = kh_get_sha1(bitmap_git.bitmaps, sha1);
+       if (hash_pos < kh_end(bitmap_git.bitmaps)) {
+               struct stored_bitmap *st = kh_value(bitmap_git.bitmaps, hash_pos);
+               bitmap_or_ewah(data->base, lookup_stored_bitmap(st));
+               return 0;
+       }
+
+       bitmap_set(data->base, bitmap_pos);
+       return 1;
+}
+
+static int should_include(struct commit *commit, void *_data)
+{
+       struct include_data *data = _data;
+       int bitmap_pos;
+
+       bitmap_pos = bitmap_position(commit->object.sha1);
+       if (bitmap_pos < 0)
+               bitmap_pos = ext_index_add_object((struct object *)commit, NULL);
+
+       if (!add_to_include_set(data, commit->object.sha1, bitmap_pos)) {
+               struct commit_list *parent = commit->parents;
+
+               while (parent) {
+                       parent->item->object.flags |= SEEN;
+                       parent = parent->next;
+               }
+
+               return 0;
+       }
+
+       return 1;
+}
+
+static struct bitmap *find_objects(struct rev_info *revs,
+                                  struct object_list *roots,
+                                  struct bitmap *seen)
+{
+       struct bitmap *base = NULL;
+       int needs_walk = 0;
+
+       struct object_list *not_mapped = NULL;
+
+       /*
+        * Go through all the roots for the walk. The ones that have bitmaps
+        * on the bitmap index will be `or`ed together to form an initial
+        * global reachability analysis.
+        *
+        * The ones without bitmaps in the index will be stored in the
+        * `not_mapped_list` for further processing.
+        */
+       while (roots) {
+               struct object *object = roots->item;
+               roots = roots->next;
+
+               if (object->type == OBJ_COMMIT) {
+                       khiter_t pos = kh_get_sha1(bitmap_git.bitmaps, object->sha1);
+
+                       if (pos < kh_end(bitmap_git.bitmaps)) {
+                               struct stored_bitmap *st = kh_value(bitmap_git.bitmaps, pos);
+                               struct ewah_bitmap *or_with = lookup_stored_bitmap(st);
+
+                               if (base == NULL)
+                                       base = ewah_to_bitmap(or_with);
+                               else
+                                       bitmap_or_ewah(base, or_with);
+
+                               object->flags |= SEEN;
+                               continue;
+                       }
+               }
+
+               object_list_insert(object, ¬_mapped);
+       }
+
+       /*
+        * Best case scenario: We found bitmaps for all the roots,
+        * so the resulting `or` bitmap has the full reachability analysis
+        */
+       if (not_mapped == NULL)
+               return base;
+
+       roots = not_mapped;
+
+       /*
+        * Let's iterate through all the roots that don't have bitmaps to
+        * check if we can determine them to be reachable from the existing
+        * global bitmap.
+        *
+        * If we cannot find them in the existing global bitmap, we'll need
+        * to push them to an actual walk and run it until we can confirm
+        * they are reachable
+        */
+       while (roots) {
+               struct object *object = roots->item;
+               int pos;
+
+               roots = roots->next;
+               pos = bitmap_position(object->sha1);
+
+               if (pos < 0 || base == NULL || !bitmap_get(base, pos)) {
+                       object->flags &= ~UNINTERESTING;
+                       add_pending_object(revs, object, "");
+                       needs_walk = 1;
+               } else {
+                       object->flags |= SEEN;
+               }
+       }
+
+       if (needs_walk) {
+               struct include_data incdata;
+
+               if (base == NULL)
+                       base = bitmap_new();
+
+               incdata.base = base;
+               incdata.seen = seen;
+
+               revs->include_check = should_include;
+               revs->include_check_data = &incdata;
+
+               if (prepare_revision_walk(revs))
+                       die("revision walk setup failed");
+
+               traverse_commit_list(revs, show_commit, show_object, base);
+       }
+
+       return base;
+}
+
+static void show_extended_objects(struct bitmap *objects,
+                                 show_reachable_fn show_reach)
+{
+       struct eindex *eindex = &bitmap_git.ext_index;
+       uint32_t i;
+
+       for (i = 0; i < eindex->count; ++i) {
+               struct object *obj;
+
+               if (!bitmap_get(objects, bitmap_git.pack->num_objects + i))
+                       continue;
+
+               obj = eindex->objects[i];
+               show_reach(obj->sha1, obj->type, 0, eindex->hashes[i], NULL, 0);
+       }
+}
+
+static void show_objects_for_type(
+       struct bitmap *objects,
+       struct ewah_bitmap *type_filter,
+       enum object_type object_type,
+       show_reachable_fn show_reach)
+{
+       size_t pos = 0, i = 0;
+       uint32_t offset;
+
+       struct ewah_iterator it;
+       eword_t filter;
+
+       if (bitmap_git.reuse_objects == bitmap_git.pack->num_objects)
+               return;
+
+       ewah_iterator_init(&it, type_filter);
+
+       while (i < objects->word_alloc && ewah_iterator_next(&filter, &it)) {
+               eword_t word = objects->words[i] & filter;
+
+               for (offset = 0; offset < BITS_IN_WORD; ++offset) {
+                       const unsigned char *sha1;
+                       struct revindex_entry *entry;
+                       uint32_t hash = 0;
+
+                       if ((word >> offset) == 0)
+                               break;
+
+                       offset += ewah_bit_ctz64(word >> offset);
+
+                       if (pos + offset < bitmap_git.reuse_objects)
+                               continue;
+
+                       entry = &bitmap_git.reverse_index->revindex[pos + offset];
+                       sha1 = nth_packed_object_sha1(bitmap_git.pack, entry->nr);
+
+                       show_reach(sha1, object_type, 0, hash, bitmap_git.pack, entry->offset);
+               }
+
+               pos += BITS_IN_WORD;
+               i++;
+       }
+}
+
+static int in_bitmapped_pack(struct object_list *roots)
+{
+       while (roots) {
+               struct object *object = roots->item;
+               roots = roots->next;
+
+               if (find_pack_entry_one(object->sha1, bitmap_git.pack) > 0)
+                       return 1;
+       }
+
+       return 0;
+}
+
+int prepare_bitmap_walk(struct rev_info *revs)
+{
+       unsigned int i;
+       unsigned int pending_nr = revs->pending.nr;
+       struct object_array_entry *pending_e = revs->pending.objects;
+
+       struct object_list *wants = NULL;
+       struct object_list *haves = NULL;
+
+       struct bitmap *wants_bitmap = NULL;
+       struct bitmap *haves_bitmap = NULL;
+
+       if (!bitmap_git.loaded) {
+               /* try to open a bitmapped pack, but don't parse it yet
+                * because we may not need to use it */
+               if (open_pack_bitmap() < 0)
+                       return -1;
+       }
+
+       for (i = 0; i < pending_nr; ++i) {
+               struct object *object = pending_e[i].item;
+
+               if (object->type == OBJ_NONE)
+                       parse_object_or_die(object->sha1, NULL);
+
+               while (object->type == OBJ_TAG) {
+                       struct tag *tag = (struct tag *) object;
+
+                       if (object->flags & UNINTERESTING)
+                               object_list_insert(object, &haves);
+                       else
+                               object_list_insert(object, &wants);
+
+                       if (!tag->tagged)
+                               die("bad tag");
+                       object = parse_object_or_die(tag->tagged->sha1, NULL);
+               }
+
+               if (object->flags & UNINTERESTING)
+                       object_list_insert(object, &haves);
+               else
+                       object_list_insert(object, &wants);
+       }
+
+       /*
+        * if we have a HAVES list, but none of those haves is contained
+        * in the packfile that has a bitmap, we don't have anything to
+        * optimize here
+        */
+       if (haves && !in_bitmapped_pack(haves))
+               return -1;
+
+       /* if we don't want anything, we're done here */
+       if (!wants)
+               return -1;
+
+       /*
+        * now we're going to use bitmaps, so load the actual bitmap entries
+        * from disk. this is the point of no return; after this the rev_list
+        * becomes invalidated and we must perform the revwalk through bitmaps
+        */
+       if (!bitmap_git.loaded && load_pack_bitmap() < 0)
+               return -1;
+
+       revs->pending.nr = 0;
+       revs->pending.alloc = 0;
+       revs->pending.objects = NULL;
+
+       if (haves) {
+               haves_bitmap = find_objects(revs, haves, NULL);
+               reset_revision_walk();
+
+               if (haves_bitmap == NULL)
+                       die("BUG: failed to perform bitmap walk");
+       }
+
+       wants_bitmap = find_objects(revs, wants, haves_bitmap);
+
+       if (!wants_bitmap)
+               die("BUG: failed to perform bitmap walk");
+
+       if (haves_bitmap)
+               bitmap_and_not(wants_bitmap, haves_bitmap);
+
+       bitmap_git.result = wants_bitmap;
+
+       bitmap_free(haves_bitmap);
+       return 0;
+}
+
+int reuse_partial_packfile_from_bitmap(struct packed_git **packfile,
+                                      uint32_t *entries,
+                                      off_t *up_to)
+{
+       /*
+        * Reuse the packfile content if we need more than
+        * 90% of its objects
+        */
+       static const double REUSE_PERCENT = 0.9;
+
+       struct bitmap *result = bitmap_git.result;
+       uint32_t reuse_threshold;
+       uint32_t i, reuse_objects = 0;
+
+       assert(result);
+
+       for (i = 0; i < result->word_alloc; ++i) {
+               if (result->words[i] != (eword_t)~0) {
+                       reuse_objects += ewah_bit_ctz64(~result->words[i]);
+                       break;
+               }
+
+               reuse_objects += BITS_IN_WORD;
+       }
+
+#ifdef GIT_BITMAP_DEBUG
+       {
+               const unsigned char *sha1;
+               struct revindex_entry *entry;
+
+               entry = &bitmap_git.reverse_index->revindex[reuse_objects];
+               sha1 = nth_packed_object_sha1(bitmap_git.pack, entry->nr);
+
+               fprintf(stderr, "Failed to reuse at %d (%016llx)\n",
+                       reuse_objects, result->words[i]);
+               fprintf(stderr, " %s\n", sha1_to_hex(sha1));
+       }
+#endif
+
+       if (!reuse_objects)
+               return -1;
+
+       if (reuse_objects >= bitmap_git.pack->num_objects) {
+               bitmap_git.reuse_objects = *entries = bitmap_git.pack->num_objects;
+               *up_to = -1; /* reuse the full pack */
+               *packfile = bitmap_git.pack;
+               return 0;
+       }
+
+       reuse_threshold = bitmap_popcount(bitmap_git.result) * REUSE_PERCENT;
+
+       if (reuse_objects < reuse_threshold)
+               return -1;
+
+       bitmap_git.reuse_objects = *entries = reuse_objects;
+       *up_to = bitmap_git.reverse_index->revindex[reuse_objects].offset;
+       *packfile = bitmap_git.pack;
+
+       return 0;
+}
+
+void traverse_bitmap_commit_list(show_reachable_fn show_reachable)
+{
+       assert(bitmap_git.result);
+
+       show_objects_for_type(bitmap_git.result, bitmap_git.commits,
+               OBJ_COMMIT, show_reachable);
+       show_objects_for_type(bitmap_git.result, bitmap_git.trees,
+               OBJ_TREE, show_reachable);
+       show_objects_for_type(bitmap_git.result, bitmap_git.blobs,
+               OBJ_BLOB, show_reachable);
+       show_objects_for_type(bitmap_git.result, bitmap_git.tags,
+               OBJ_TAG, show_reachable);
+
+       show_extended_objects(bitmap_git.result, show_reachable);
+
+       bitmap_free(bitmap_git.result);
+       bitmap_git.result = NULL;
+}
+
+static uint32_t count_object_type(struct bitmap *objects,
+                                 enum object_type type)
+{
+       struct eindex *eindex = &bitmap_git.ext_index;
+
+       uint32_t i = 0, count = 0;
+       struct ewah_iterator it;
+       eword_t filter;
+
+       switch (type) {
+       case OBJ_COMMIT:
+               ewah_iterator_init(&it, bitmap_git.commits);
+               break;
+
+       case OBJ_TREE:
+               ewah_iterator_init(&it, bitmap_git.trees);
+               break;
+
+       case OBJ_BLOB:
+               ewah_iterator_init(&it, bitmap_git.blobs);
+               break;
+
+       case OBJ_TAG:
+               ewah_iterator_init(&it, bitmap_git.tags);
+               break;
+
+       default:
+               return 0;
+       }
+
+       while (i < objects->word_alloc && ewah_iterator_next(&filter, &it)) {
+               eword_t word = objects->words[i++] & filter;
+               count += ewah_bit_popcount64(word);
+       }
+
+       for (i = 0; i < eindex->count; ++i) {
+               if (eindex->objects[i]->type == type &&
+                       bitmap_get(objects, bitmap_git.pack->num_objects + i))
+                       count++;
+       }
+
+       return count;
+}
+
+void count_bitmap_commit_list(uint32_t *commits, uint32_t *trees,
+                             uint32_t *blobs, uint32_t *tags)
+{
+       assert(bitmap_git.result);
+
+       if (commits)
+               *commits = count_object_type(bitmap_git.result, OBJ_COMMIT);
+
+       if (trees)
+               *trees = count_object_type(bitmap_git.result, OBJ_TREE);
+
+       if (blobs)
+               *blobs = count_object_type(bitmap_git.result, OBJ_BLOB);
+
+       if (tags)
+               *tags = count_object_type(bitmap_git.result, OBJ_TAG);
+}
+
+struct bitmap_test_data {
+       struct bitmap *base;
+       struct progress *prg;
+       size_t seen;
+};
+
+static void test_show_object(struct object *object,
+                            const struct name_path *path,
+                            const char *last, void *data)
+{
+       struct bitmap_test_data *tdata = data;
+       int bitmap_pos;
+
+       bitmap_pos = bitmap_position(object->sha1);
+       if (bitmap_pos < 0)
+               die("Object not in bitmap: %s\n", sha1_to_hex(object->sha1));
+
+       bitmap_set(tdata->base, bitmap_pos);
+       display_progress(tdata->prg, ++tdata->seen);
+}
+
+static void test_show_commit(struct commit *commit, void *data)
+{
+       struct bitmap_test_data *tdata = data;
+       int bitmap_pos;
+
+       bitmap_pos = bitmap_position(commit->object.sha1);
+       if (bitmap_pos < 0)
+               die("Object not in bitmap: %s\n", sha1_to_hex(commit->object.sha1));
+
+       bitmap_set(tdata->base, bitmap_pos);
+       display_progress(tdata->prg, ++tdata->seen);
+}
+
+void test_bitmap_walk(struct rev_info *revs)
+{
+       struct object *root;
+       struct bitmap *result = NULL;
+       khiter_t pos;
+       size_t result_popcnt;
+       struct bitmap_test_data tdata;
+
+       if (prepare_bitmap_git())
+               die("failed to load bitmap indexes");
+
+       if (revs->pending.nr != 1)
+               die("you must specify exactly one commit to test");
+
+       fprintf(stderr, "Bitmap v%d test (%d entries loaded)\n",
+               bitmap_git.version, bitmap_git.entry_count);
+
+       root = revs->pending.objects[0].item;
+       pos = kh_get_sha1(bitmap_git.bitmaps, root->sha1);
+
+       if (pos < kh_end(bitmap_git.bitmaps)) {
+               struct stored_bitmap *st = kh_value(bitmap_git.bitmaps, pos);
+               struct ewah_bitmap *bm = lookup_stored_bitmap(st);
+
+               fprintf(stderr, "Found bitmap for %s. %d bits / %08x checksum\n",
+                       sha1_to_hex(root->sha1), (int)bm->bit_size, ewah_checksum(bm));
+
+               result = ewah_to_bitmap(bm);
+       }
+
+       if (result == NULL)
+               die("Commit %s doesn't have an indexed bitmap", sha1_to_hex(root->sha1));
+
+       revs->tag_objects = 1;
+       revs->tree_objects = 1;
+       revs->blob_objects = 1;
+
+       result_popcnt = bitmap_popcount(result);
+
+       if (prepare_revision_walk(revs))
+               die("revision walk setup failed");
+
+       tdata.base = bitmap_new();
+       tdata.prg = start_progress("Verifying bitmap entries", result_popcnt);
+       tdata.seen = 0;
+
+       traverse_commit_list(revs, &test_show_commit, &test_show_object, &tdata);
+
+       stop_progress(&tdata.prg);
+
+       if (bitmap_equals(result, tdata.base))
+               fprintf(stderr, "OK!\n");
+       else
+               fprintf(stderr, "Mismatch!\n");
+}