Make git-pack-objects a builtin

Signed-off-by: Matthias Kestenholz <matthias@spinlock.ch>
Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 1376 insertions, 0 deletions

diff --git a/builtin-pack-objects.c b/builtin-pack-objects.c
new file mode 100644
index 0000000000..2301cd5c0f
--- /dev/null
+++ b/builtin-pack-objects.c
@@ -0,0 +1,1376 @@
+#include "builtin.h"
+#include "cache.h"
+#include "object.h"
+#include "blob.h"
+#include "commit.h"
+#include "tag.h"
+#include "tree.h"
+#include "delta.h"
+#include "pack.h"
+#include "csum-file.h"
+#include "tree-walk.h"
+#include <sys/time.h>
+#include <signal.h>
+
+static const char pack_usage[] = "git-pack-objects [-q] [--no-reuse-delta] [--non-empty] [--local] [--incremental] [--window=N] [--depth=N] {--stdout | base-name} < object-list";
+
+struct object_entry {
+	unsigned char sha1[20];
+	unsigned long size;	/* uncompressed size */
+	unsigned long offset;	/* offset into the final pack file;
+				 * nonzero if already written.
+				 */
+	unsigned int depth;	/* delta depth */
+	unsigned int delta_limit;	/* base adjustment for in-pack delta */
+	unsigned int hash;	/* name hint hash */
+	enum object_type type;
+	enum object_type in_pack_type;	/* could be delta */
+	unsigned long delta_size;	/* delta data size (uncompressed) */
+	struct object_entry *delta;	/* delta base object */
+	struct packed_git *in_pack; 	/* already in pack */
+	unsigned int in_pack_offset;
+	struct object_entry *delta_child; /* deltified objects who bases me */
+	struct object_entry *delta_sibling; /* other deltified objects who
+					     * uses the same base as me
+					     */
+	int preferred_base;	/* we do not pack this, but is encouraged to
+				 * be used as the base objectto delta huge
+				 * objects against.
+				 */
+};
+
+/*
+ * Objects we are going to pack are collected in objects array (dynamically
+ * expanded).  nr_objects & nr_alloc controls this array.  They are stored
+ * in the order we see -- typically rev-list --objects order that gives us
+ * nice "minimum seek" order.
+ *
+ * sorted-by-sha ans sorted-by-type are arrays of pointers that point at
+ * elements in the objects array.  The former is used to build the pack
+ * index (lists object names in the ascending order to help offset lookup),
+ * and the latter is used to group similar things together by try_delta()
+ * heuristics.
+ */
+
+static unsigned char object_list_sha1[20];
+static int non_empty = 0;
+static int no_reuse_delta = 0;
+static int local = 0;
+static int incremental = 0;
+static struct object_entry **sorted_by_sha, **sorted_by_type;
+static struct object_entry *objects = NULL;
+static int nr_objects = 0, nr_alloc = 0, nr_result = 0;
+static const char *base_name;
+static unsigned char pack_file_sha1[20];
+static int progress = 1;
+static volatile sig_atomic_t progress_update = 0;
+static int window = 10;
+
+/*
+ * The object names in objects array are hashed with this hashtable,
+ * to help looking up the entry by object name.  Binary search from
+ * sorted_by_sha is also possible but this was easier to code and faster.
+ * This hashtable is built after all the objects are seen.
+ */
+static int *object_ix = NULL;
+static int object_ix_hashsz = 0;
+
+/*
+ * Pack index for existing packs give us easy access to the offsets into
+ * corresponding pack file where each object's data starts, but the entries
+ * do not store the size of the compressed representation (uncompressed
+ * size is easily available by examining the pack entry header).  We build
+ * a hashtable of existing packs (pack_revindex), and keep reverse index
+ * here -- pack index file is sorted by object name mapping to offset; this
+ * pack_revindex[].revindex array is an ordered list of offsets, so if you
+ * know the offset of an object, next offset is where its packed
+ * representation ends.
+ */
+struct pack_revindex {
+	struct packed_git *p;
+	unsigned long *revindex;
+} *pack_revindex = NULL;
+static int pack_revindex_hashsz = 0;
+
+/*
+ * stats
+ */
+static int written = 0;
+static int written_delta = 0;
+static int reused = 0;
+static int reused_delta = 0;
+
+static int pack_revindex_ix(struct packed_git *p)
+{
+	unsigned long ui = (unsigned long)p;
+	int i;
+
+	ui = ui ^ (ui >> 16); /* defeat structure alignment */
+	i = (int)(ui % pack_revindex_hashsz);
+	while (pack_revindex[i].p) {
+		if (pack_revindex[i].p == p)
+			return i;
+		if (++i == pack_revindex_hashsz)
+			i = 0;
+	}
+	return -1 - i;
+}
+
+static void prepare_pack_ix(void)
+{
+	int num;
+	struct packed_git *p;
+	for (num = 0, p = packed_git; p; p = p->next)
+		num++;
+	if (!num)
+		return;
+	pack_revindex_hashsz = num * 11;
+	pack_revindex = xcalloc(sizeof(*pack_revindex), pack_revindex_hashsz);
+	for (p = packed_git; p; p = p->next) {
+		num = pack_revindex_ix(p);
+		num = - 1 - num;
+		pack_revindex[num].p = p;
+	}
+	/* revindex elements are lazily initialized */
+}
+
+static int cmp_offset(const void *a_, const void *b_)
+{
+	unsigned long a = *(unsigned long *) a_;
+	unsigned long b = *(unsigned long *) b_;
+	if (a < b)
+		return -1;
+	else if (a == b)
+		return 0;
+	else
+		return 1;
+}
+
+/*
+ * Ordered list of offsets of objects in the pack.
+ */
+static void prepare_pack_revindex(struct pack_revindex *rix)
+{
+	struct packed_git *p = rix->p;
+	int num_ent = num_packed_objects(p);
+	int i;
+	void *index = p->index_base + 256;
+
+	rix->revindex = xmalloc(sizeof(unsigned long) * (num_ent + 1));
+	for (i = 0; i < num_ent; i++) {
+		unsigned int hl = *((unsigned int *)((char *) index + 24*i));
+		rix->revindex[i] = ntohl(hl);
+	}
+	/* This knows the pack format -- the 20-byte trailer
+	 * follows immediately after the last object data.
+	 */
+	rix->revindex[num_ent] = p->pack_size - 20;
+	qsort(rix->revindex, num_ent, sizeof(unsigned long), cmp_offset);
+}
+
+static unsigned long find_packed_object_size(struct packed_git *p,
+					     unsigned long ofs)
+{
+	int num;
+	int lo, hi;
+	struct pack_revindex *rix;
+	unsigned long *revindex;
+	num = pack_revindex_ix(p);
+	if (num < 0)
+		die("internal error: pack revindex uninitialized");
+	rix = &pack_revindex[num];
+	if (!rix->revindex)
+		prepare_pack_revindex(rix);
+	revindex = rix->revindex;
+	lo = 0;
+	hi = num_packed_objects(p) + 1;
+	do {
+		int mi = (lo + hi) / 2;
+		if (revindex[mi] == ofs) {
+			return revindex[mi+1] - ofs;
+		}
+		else if (ofs < revindex[mi])
+			hi = mi;
+		else
+			lo = mi + 1;
+	} while (lo < hi);
+	die("internal error: pack revindex corrupt");
+}
+
+static void *delta_against(void *buf, unsigned long size, struct object_entry *entry)
+{
+	unsigned long othersize, delta_size;
+	char type[10];
+	void *otherbuf = read_sha1_file(entry->delta->sha1, type, &othersize);
+	void *delta_buf;
+
+	if (!otherbuf)
+		die("unable to read %s", sha1_to_hex(entry->delta->sha1));
+        delta_buf = diff_delta(otherbuf, othersize,
+			       buf, size, &delta_size, 0);
+        if (!delta_buf || delta_size != entry->delta_size)
+        	die("delta size changed");
+        free(buf);
+        free(otherbuf);
+	return delta_buf;
+}
+
+/*
+ * The per-object header is a pretty dense thing, which is
+ *  - first byte: low four bits are "size", then three bits of "type",
+ *    and the high bit is "size continues".
+ *  - each byte afterwards: low seven bits are size continuation,
+ *    with the high bit being "size continues"
+ */
+static int encode_header(enum object_type type, unsigned long size, unsigned char *hdr)
+{
+	int n = 1;
+	unsigned char c;
+
+	if (type < OBJ_COMMIT || type > OBJ_DELTA)
+		die("bad type %d", type);
+
+	c = (type << 4) | (size & 15);
+	size >>= 4;
+	while (size) {
+		*hdr++ = c | 0x80;
+		c = size & 0x7f;
+		size >>= 7;
+		n++;
+	}
+	*hdr = c;
+	return n;
+}
+
+static unsigned long write_object(struct sha1file *f,
+				  struct object_entry *entry)
+{
+	unsigned long size;
+	char type[10];
+	void *buf;
+	unsigned char header[10];
+	unsigned hdrlen, datalen;
+	enum object_type obj_type;
+	int to_reuse = 0;
+
+	if (entry->preferred_base)
+		return 0;
+
+	obj_type = entry->type;
+	if (! entry->in_pack)
+		to_reuse = 0;	/* can't reuse what we don't have */
+	else if (obj_type == OBJ_DELTA)
+		to_reuse = 1;	/* check_object() decided it for us */
+	else if (obj_type != entry->in_pack_type)
+		to_reuse = 0;	/* pack has delta which is unusable */
+	else if (entry->delta)
+		to_reuse = 0;	/* we want to pack afresh */
+	else
+		to_reuse = 1;	/* we have it in-pack undeltified,
+				 * and we do not need to deltify it.
+				 */
+
+	if (! to_reuse) {
+		buf = read_sha1_file(entry->sha1, type, &size);
+		if (!buf)
+			die("unable to read %s", sha1_to_hex(entry->sha1));
+		if (size != entry->size)
+			die("object %s size inconsistency (%lu vs %lu)",
+			    sha1_to_hex(entry->sha1), size, entry->size);
+		if (entry->delta) {
+			buf = delta_against(buf, size, entry);
+			size = entry->delta_size;
+			obj_type = OBJ_DELTA;
+		}
+		/*
+		 * The object header is a byte of 'type' followed by zero or
+		 * more bytes of length.  For deltas, the 20 bytes of delta
+		 * sha1 follows that.
+		 */
+		hdrlen = encode_header(obj_type, size, header);
+		sha1write(f, header, hdrlen);
+
+		if (entry->delta) {
+			sha1write(f, entry->delta, 20);
+			hdrlen += 20;
+		}
+		datalen = sha1write_compressed(f, buf, size);
+		free(buf);
+	}
+	else {
+		struct packed_git *p = entry->in_pack;
+		use_packed_git(p);
+
+		datalen = find_packed_object_size(p, entry->in_pack_offset);
+		buf = (char *) p->pack_base + entry->in_pack_offset;
+		sha1write(f, buf, datalen);
+		unuse_packed_git(p);
+		hdrlen = 0; /* not really */
+		if (obj_type == OBJ_DELTA)
+			reused_delta++;
+		reused++;
+	}
+	if (obj_type == OBJ_DELTA)
+		written_delta++;
+	written++;
+	return hdrlen + datalen;
+}
+
+static unsigned long write_one(struct sha1file *f,
+			       struct object_entry *e,
+			       unsigned long offset)
+{
+	if (e->offset)
+		/* offset starts from header size and cannot be zero
+		 * if it is written already.
+		 */
+		return offset;
+	e->offset = offset;
+	offset += write_object(f, e);
+	/* if we are deltified, write out its base object. */
+	if (e->delta)
+		offset = write_one(f, e->delta, offset);
+	return offset;
+}
+
+static void write_pack_file(void)
+{
+	int i;
+	struct sha1file *f;
+	unsigned long offset;
+	struct pack_header hdr;
+	unsigned last_percent = 999;
+	int do_progress = 0;
+
+	if (!base_name)
+		f = sha1fd(1, "<stdout>");
+	else {
+		f = sha1create("%s-%s.%s", base_name,
+			       sha1_to_hex(object_list_sha1), "pack");
+		do_progress = progress;
+	}
+	if (do_progress)
+		fprintf(stderr, "Writing %d objects.\n", nr_result);
+
+	hdr.hdr_signature = htonl(PACK_SIGNATURE);
+	hdr.hdr_version = htonl(PACK_VERSION);
+	hdr.hdr_entries = htonl(nr_result);
+	sha1write(f, &hdr, sizeof(hdr));
+	offset = sizeof(hdr);
+	if (!nr_result)
+		goto done;
+	for (i = 0; i < nr_objects; i++) {
+		offset = write_one(f, objects + i, offset);
+		if (do_progress) {
+			unsigned percent = written * 100 / nr_result;
+			if (progress_update || percent != last_percent) {
+				fprintf(stderr, "%4u%% (%u/%u) done\r",
+					percent, written, nr_result);
+				progress_update = 0;
+				last_percent = percent;
+			}
+		}
+	}
+	if (do_progress)
+		fputc('\n', stderr);
+ done:
+	sha1close(f, pack_file_sha1, 1);
+}
+
+static void write_index_file(void)
+{
+	int i;
+	struct sha1file *f = sha1create("%s-%s.%s", base_name,
+					sha1_to_hex(object_list_sha1), "idx");
+	struct object_entry **list = sorted_by_sha;
+	struct object_entry **last = list + nr_result;
+	unsigned int array[256];
+
+	/*
+	 * Write the first-level table (the list is sorted,
+	 * but we use a 256-entry lookup to be able to avoid
+	 * having to do eight extra binary search iterations).
+	 */
+	for (i = 0; i < 256; i++) {
+		struct object_entry **next = list;
+		while (next < last) {
+			struct object_entry *entry = *next;
+			if (entry->sha1[0] != i)
+				break;
+			next++;
+		}
+		array[i] = htonl(next - sorted_by_sha);
+		list = next;
+	}
+	sha1write(f, array, 256 * sizeof(int));
+
+	/*
+	 * Write the actual SHA1 entries..
+	 */
+	list = sorted_by_sha;
+	for (i = 0; i < nr_result; i++) {
+		struct object_entry *entry = *list++;
+		unsigned int offset = htonl(entry->offset);
+		sha1write(f, &offset, 4);
+		sha1write(f, entry->sha1, 20);
+	}
+	sha1write(f, pack_file_sha1, 20);
+	sha1close(f, NULL, 1);
+}
+
+static int locate_object_entry_hash(const unsigned char *sha1)
+{
+	int i;
+	unsigned int ui;
+	memcpy(&ui, sha1, sizeof(unsigned int));
+	i = ui % object_ix_hashsz;
+	while (0 < object_ix[i]) {
+		if (!memcmp(sha1, objects[object_ix[i]-1].sha1, 20))
+			return i;
+		if (++i == object_ix_hashsz)
+			i = 0;
+	}
+	return -1 - i;
+}
+
+static struct object_entry *locate_object_entry(const unsigned char *sha1)
+{
+	int i;
+
+	if (!object_ix_hashsz)
+		return NULL;
+
+	i = locate_object_entry_hash(sha1);
+	if (0 <= i)
+		return &objects[object_ix[i]-1];
+	return NULL;
+}
+
+static void rehash_objects(void)
+{
+	int i;
+	struct object_entry *oe;
+
+	object_ix_hashsz = nr_objects * 3;
+	if (object_ix_hashsz < 1024)
+		object_ix_hashsz = 1024;
+	object_ix = xrealloc(object_ix, sizeof(int) * object_ix_hashsz);
+	memset(object_ix, 0, sizeof(int) * object_ix_hashsz);
+	for (i = 0, oe = objects; i < nr_objects; i++, oe++) {
+		int ix = locate_object_entry_hash(oe->sha1);
+		if (0 <= ix)
+			continue;
+		ix = -1 - ix;
+		object_ix[ix] = i + 1;
+	}
+}
+
+static unsigned name_hash(const char *name)
+{
+	unsigned char c;
+	unsigned hash = 0;
+
+	/*
+	 * This effectively just creates a sortable number from the
+	 * last sixteen non-whitespace characters. Last characters
+	 * count "most", so things that end in ".c" sort together.
+	 */
+	while ((c = *name++) != 0) {
+		if (isspace(c))
+			continue;
+		hash = (hash >> 2) + (c << 24);
+	}
+	return hash;
+}
+
+static int add_object_entry(const unsigned char *sha1, unsigned hash, int exclude)
+{
+	unsigned int idx = nr_objects;
+	struct object_entry *entry;
+	struct packed_git *p;
+	unsigned int found_offset = 0;
+	struct packed_git *found_pack = NULL;
+	int ix, status = 0;
+
+	if (!exclude) {
+		for (p = packed_git; p; p = p->next) {
+			struct pack_entry e;
+			if (find_pack_entry_one(sha1, &e, p)) {
+				if (incremental)
+					return 0;
+				if (local && !p->pack_local)
+					return 0;
+				if (!found_pack) {
+					found_offset = e.offset;
+					found_pack = e.p;
+				}
+			}
+		}
+	}
+	if ((entry = locate_object_entry(sha1)) != NULL)
+		goto already_added;
+
+	if (idx >= nr_alloc) {
+		unsigned int needed = (idx + 1024) * 3 / 2;
+		objects = xrealloc(objects, needed * sizeof(*entry));
+		nr_alloc = needed;
+	}
+	entry = objects + idx;
+	nr_objects = idx + 1;
+	memset(entry, 0, sizeof(*entry));
+	memcpy(entry->sha1, sha1, 20);
+	entry->hash = hash;
+
+	if (object_ix_hashsz * 3 <= nr_objects * 4)
+		rehash_objects();
+	else {
+		ix = locate_object_entry_hash(entry->sha1);
+		if (0 <= ix)
+			die("internal error in object hashing.");
+		object_ix[-1 - ix] = idx + 1;
+	}
+	status = 1;
+
+ already_added:
+	if (progress_update) {
+		fprintf(stderr, "Counting objects...%d\r", nr_objects);
+		progress_update = 0;
+	}
+	if (exclude)
+		entry->preferred_base = 1;
+	else {
+		if (found_pack) {
+			entry->in_pack = found_pack;
+			entry->in_pack_offset = found_offset;
+		}
+	}
+	return status;
+}
+
+struct pbase_tree_cache {
+	unsigned char sha1[20];
+	int ref;
+	int temporary;
+	void *tree_data;
+	unsigned long tree_size;
+};
+
+static struct pbase_tree_cache *(pbase_tree_cache[256]);
+static int pbase_tree_cache_ix(const unsigned char *sha1)
+{
+	return sha1[0] % ARRAY_SIZE(pbase_tree_cache);
+}
+static int pbase_tree_cache_ix_incr(int ix)
+{
+	return (ix+1) % ARRAY_SIZE(pbase_tree_cache);
+}
+
+static struct pbase_tree {
+	struct pbase_tree *next;
+	/* This is a phony "cache" entry; we are not
+	 * going to evict it nor find it through _get()
+	 * mechanism -- this is for the toplevel node that
+	 * would almost always change with any commit.
+	 */
+	struct pbase_tree_cache pcache;
+} *pbase_tree;
+
+static struct pbase_tree_cache *pbase_tree_get(const unsigned char *sha1)
+{
+	struct pbase_tree_cache *ent, *nent;
+	void *data;
+	unsigned long size;
+	char type[20];
+	int neigh;
+	int my_ix = pbase_tree_cache_ix(sha1);
+	int available_ix = -1;
+
+	/* pbase-tree-cache acts as a limited hashtable.
+	 * your object will be found at your index or within a few
+	 * slots after that slot if it is cached.
+	 */
+	for (neigh = 0; neigh < 8; neigh++) {
+		ent = pbase_tree_cache[my_ix];
+		if (ent && !memcmp(ent->sha1, sha1, 20)) {
+			ent->ref++;
+			return ent;
+		}
+		else if (((available_ix < 0) && (!ent || !ent->ref)) ||
+			 ((0 <= available_ix) &&
+			  (!ent && pbase_tree_cache[available_ix])))
+			available_ix = my_ix;
+		if (!ent)
+			break;
+		my_ix = pbase_tree_cache_ix_incr(my_ix);
+	}
+
+	/* Did not find one.  Either we got a bogus request or
+	 * we need to read and perhaps cache.
+	 */
+	data = read_sha1_file(sha1, type, &size);
+	if (!data)
+		return NULL;
+	if (strcmp(type, tree_type)) {
+		free(data);
+		return NULL;
+	}
+
+	/* We need to either cache or return a throwaway copy */
+
+	if (available_ix < 0)
+		ent = NULL;
+	else {
+		ent = pbase_tree_cache[available_ix];
+		my_ix = available_ix;
+	}
+
+	if (!ent) {
+		nent = xmalloc(sizeof(*nent));
+		nent->temporary = (available_ix < 0);
+	}
+	else {
+		/* evict and reuse */
+		free(ent->tree_data);
+		nent = ent;
+	}
+	memcpy(nent->sha1, sha1, 20);
+	nent->tree_data = data;
+	nent->tree_size = size;
+	nent->ref = 1;
+	if (!nent->temporary)
+		pbase_tree_cache[my_ix] = nent;
+	return nent;
+}
+
+static void pbase_tree_put(struct pbase_tree_cache *cache)
+{
+	if (!cache->temporary) {
+		cache->ref--;
+		return;
+	}
+	free(cache->tree_data);
+	free(cache);
+}
+
+static int name_cmp_len(const char *name)
+{
+	int i;
+	for (i = 0; name[i] && name[i] != '\n' && name[i] != '/'; i++)
+		;
+	return i;
+}
+
+static void add_pbase_object(struct tree_desc *tree,
+			     const char *name,
+			     int cmplen,
+			     const char *fullname)
+{
+	struct name_entry entry;
+
+	while (tree_entry(tree,&entry)) {
+		unsigned long size;
+		char type[20];
+
+		if (entry.pathlen != cmplen ||
+		    memcmp(entry.path, name, cmplen) ||
+		    !has_sha1_file(entry.sha1) ||
+		    sha1_object_info(entry.sha1, type, &size))
+			continue;
+		if (name[cmplen] != '/') {
+			unsigned hash = name_hash(fullname);
+			add_object_entry(entry.sha1, hash, 1);
+			return;
+		}
+		if (!strcmp(type, tree_type)) {
+			struct tree_desc sub;
+			struct pbase_tree_cache *tree;
+			const char *down = name+cmplen+1;
+			int downlen = name_cmp_len(down);
+
+			tree = pbase_tree_get(entry.sha1);
+			if (!tree)
+				return;
+			sub.buf = tree->tree_data;
+			sub.size = tree->tree_size;
+
+			add_pbase_object(&sub, down, downlen, fullname);
+			pbase_tree_put(tree);
+		}
+	}
+}
+
+static unsigned *done_pbase_paths;
+static int done_pbase_paths_num;
+static int done_pbase_paths_alloc;
+static int done_pbase_path_pos(unsigned hash)
+{
+	int lo = 0;
+	int hi = done_pbase_paths_num;
+	while (lo < hi) {
+		int mi = (hi + lo) / 2;
+		if (done_pbase_paths[mi] == hash)
+			return mi;
+		if (done_pbase_paths[mi] < hash)
+			hi = mi;
+		else
+			lo = mi + 1;
+	}
+	return -lo-1;
+}
+
+static int check_pbase_path(unsigned hash)
+{
+	int pos = (!done_pbase_paths) ? -1 : done_pbase_path_pos(hash);
+	if (0 <= pos)
+		return 1;
+	pos = -pos - 1;
+	if (done_pbase_paths_alloc <= done_pbase_paths_num) {
+		done_pbase_paths_alloc = alloc_nr(done_pbase_paths_alloc);
+		done_pbase_paths = xrealloc(done_pbase_paths,
+					    done_pbase_paths_alloc *
+					    sizeof(unsigned));
+	}
+	done_pbase_paths_num++;
+	if (pos < done_pbase_paths_num)
+		memmove(done_pbase_paths + pos + 1,
+			done_pbase_paths + pos,
+			(done_pbase_paths_num - pos - 1) * sizeof(unsigned));
+	done_pbase_paths[pos] = hash;
+	return 0;
+}
+
+static void add_preferred_base_object(char *name, unsigned hash)
+{
+	struct pbase_tree *it;
+	int cmplen = name_cmp_len(name);
+
+	if (check_pbase_path(hash))
+		return;
+
+	for (it = pbase_tree; it; it = it->next) {
+		if (cmplen == 0) {
+			hash = name_hash("");
+			add_object_entry(it->pcache.sha1, hash, 1);
+		}
+		else {
+			struct tree_desc tree;
+			tree.buf = it->pcache.tree_data;
+			tree.size = it->pcache.tree_size;
+			add_pbase_object(&tree, name, cmplen, name);
+		}
+	}
+}
+
+static void add_preferred_base(unsigned char *sha1)
+{
+	struct pbase_tree *it;
+	void *data;
+	unsigned long size;
+	unsigned char tree_sha1[20];
+
+	data = read_object_with_reference(sha1, tree_type, &size, tree_sha1);
+	if (!data)
+		return;
+
+	for (it = pbase_tree; it; it = it->next) {
+		if (!memcmp(it->pcache.sha1, tree_sha1, 20)) {
+			free(data);
+			return;
+		}
+	}
+
+	it = xcalloc(1, sizeof(*it));
+	it->next = pbase_tree;
+	pbase_tree = it;
+
+	memcpy(it->pcache.sha1, tree_sha1, 20);
+	it->pcache.tree_data = data;
+	it->pcache.tree_size = size;
+}
+
+static void check_object(struct object_entry *entry)
+{
+	char type[20];
+
+	if (entry->in_pack && !entry->preferred_base) {
+		unsigned char base[20];
+		unsigned long size;
+		struct object_entry *base_entry;
+
+		/* We want in_pack_type even if we do not reuse delta.
+		 * There is no point not reusing non-delta representations.
+		 */
+		check_reuse_pack_delta(entry->in_pack,
+				       entry->in_pack_offset,
+				       base, &size,
+				       &entry->in_pack_type);
+
+		/* Check if it is delta, and the base is also an object
+		 * we are going to pack.  If so we will reuse the existing
+		 * delta.
+		 */
+		if (!no_reuse_delta &&
+		    entry->in_pack_type == OBJ_DELTA &&
+		    (base_entry = locate_object_entry(base)) &&
+		    (!base_entry->preferred_base)) {
+
+			/* Depth value does not matter - find_deltas()
+			 * will never consider reused delta as the
+			 * base object to deltify other objects
+			 * against, in order to avoid circular deltas.
+			 */
+
+			/* uncompressed size of the delta data */
+			entry->size = entry->delta_size = size;
+			entry->delta = base_entry;
+			entry->type = OBJ_DELTA;
+
+			entry->delta_sibling = base_entry->delta_child;
+			base_entry->delta_child = entry;
+
+			return;
+		}
+		/* Otherwise we would do the usual */
+	}
+
+	if (sha1_object_info(entry->sha1, type, &entry->size))
+		die("unable to get type of object %s",
+		    sha1_to_hex(entry->sha1));
+
+	if (!strcmp(type, commit_type)) {
+		entry->type = OBJ_COMMIT;
+	} else if (!strcmp(type, tree_type)) {
+		entry->type = OBJ_TREE;
+	} else if (!strcmp(type, blob_type)) {
+		entry->type = OBJ_BLOB;
+	} else if (!strcmp(type, tag_type)) {
+		entry->type = OBJ_TAG;
+	} else
+		die("unable to pack object %s of type %s",
+		    sha1_to_hex(entry->sha1), type);
+}
+
+static unsigned int check_delta_limit(struct object_entry *me, unsigned int n)
+{
+	struct object_entry *child = me->delta_child;
+	unsigned int m = n;
+	while (child) {
+		unsigned int c = check_delta_limit(child, n + 1);
+		if (m < c)
+			m = c;
+		child = child->delta_sibling;
+	}
+	return m;
+}
+
+static void get_object_details(void)
+{
+	int i;
+	struct object_entry *entry;
+
+	prepare_pack_ix();
+	for (i = 0, entry = objects; i < nr_objects; i++, entry++)
+		check_object(entry);
+
+	if (nr_objects == nr_result) {
+		/*
+		 * Depth of objects that depend on the entry -- this
+		 * is subtracted from depth-max to break too deep
+		 * delta chain because of delta data reusing.
+		 * However, we loosen this restriction when we know we
+		 * are creating a thin pack -- it will have to be
+		 * expanded on the other end anyway, so do not
+		 * artificially cut the delta chain and let it go as
+		 * deep as it wants.
+		 */
+		for (i = 0, entry = objects; i < nr_objects; i++, entry++)
+			if (!entry->delta && entry->delta_child)
+				entry->delta_limit =
+					check_delta_limit(entry, 1);
+	}
+}
+
+typedef int (*entry_sort_t)(const struct object_entry *, const struct object_entry *);
+
+static entry_sort_t current_sort;
+
+static int sort_comparator(const void *_a, const void *_b)
+{
+	struct object_entry *a = *(struct object_entry **)_a;
+	struct object_entry *b = *(struct object_entry **)_b;
+	return current_sort(a,b);
+}
+
+static struct object_entry **create_sorted_list(entry_sort_t sort)
+{
+	struct object_entry **list = xmalloc(nr_objects * sizeof(struct object_entry *));
+	int i;
+
+	for (i = 0; i < nr_objects; i++)
+		list[i] = objects + i;
+	current_sort = sort;
+	qsort(list, nr_objects, sizeof(struct object_entry *), sort_comparator);
+	return list;
+}
+
+static int sha1_sort(const struct object_entry *a, const struct object_entry *b)
+{
+	return memcmp(a->sha1, b->sha1, 20);
+}
+
+static struct object_entry **create_final_object_list(void)
+{
+	struct object_entry **list;
+	int i, j;
+
+	for (i = nr_result = 0; i < nr_objects; i++)
+		if (!objects[i].preferred_base)
+			nr_result++;
+	list = xmalloc(nr_result * sizeof(struct object_entry *));
+	for (i = j = 0; i < nr_objects; i++) {
+		if (!objects[i].preferred_base)
+			list[j++] = objects + i;
+	}
+	current_sort = sha1_sort;
+	qsort(list, nr_result, sizeof(struct object_entry *), sort_comparator);
+	return list;
+}
+
+static int type_size_sort(const struct object_entry *a, const struct object_entry *b)
+{
+	if (a->type < b->type)
+		return -1;
+	if (a->type > b->type)
+		return 1;
+	if (a->hash < b->hash)
+		return -1;
+	if (a->hash > b->hash)
+		return 1;
+	if (a->preferred_base < b->preferred_base)
+		return -1;
+	if (a->preferred_base > b->preferred_base)
+		return 1;
+	if (a->size < b->size)
+		return -1;
+	if (a->size > b->size)
+		return 1;
+	return a < b ? -1 : (a > b);
+}
+
+struct unpacked {
+	struct object_entry *entry;
+	void *data;
+	struct delta_index *index;
+};
+
+/*
+ * We search for deltas _backwards_ in a list sorted by type and
+ * by size, so that we see progressively smaller and smaller files.
+ * That's because we prefer deltas to be from the bigger file
+ * to the smaller - deletes are potentially cheaper, but perhaps
+ * more importantly, the bigger file is likely the more recent
+ * one.
+ */
+static int try_delta(struct unpacked *trg, struct unpacked *src,
+		     unsigned max_depth)
+{
+	struct object_entry *trg_entry = trg->entry;
+	struct object_entry *src_entry = src->entry;
+	unsigned long trg_size, src_size, delta_size, sizediff, max_size, sz;
+	char type[10];
+	void *delta_buf;
+
+	/* Don't bother doing diffs between different types */
+	if (trg_entry->type != src_entry->type)
+		return -1;
+
+	/* We do not compute delta to *create* objects we are not
+	 * going to pack.
+	 */
+	if (trg_entry->preferred_base)
+		return -1;
+
+	/*
+	 * We do not bother to try a delta that we discarded
+	 * on an earlier try, but only when reusing delta data.
+	 */
+	if (!no_reuse_delta && trg_entry->in_pack &&
+	    trg_entry->in_pack == src_entry->in_pack)
+		return 0;
+
+	/*
+	 * If the current object is at pack edge, take the depth the
+	 * objects that depend on the current object into account --
+	 * otherwise they would become too deep.
+	 */
+	if (trg_entry->delta_child) {
+		if (max_depth <= trg_entry->delta_limit)
+			return 0;
+		max_depth -= trg_entry->delta_limit;
+	}
+	if (src_entry->depth >= max_depth)
+		return 0;
+
+	/* Now some size filtering heuristics. */
+	trg_size = trg_entry->size;
+	max_size = trg_size/2 - 20;
+	max_size = max_size * (max_depth - src_entry->depth) / max_depth;
+	if (max_size == 0)
+		return 0;
+	if (trg_entry->delta && trg_entry->delta_size <= max_size)
+		max_size = trg_entry->delta_size-1;
+	src_size = src_entry->size;
+	sizediff = src_size < trg_size ? trg_size - src_size : 0;
+	if (sizediff >= max_size)
+		return 0;
+
+	/* Load data if not already done */
+	if (!trg->data) {
+		trg->data = read_sha1_file(trg_entry->sha1, type, &sz);
+		if (sz != trg_size)
+			die("object %s inconsistent object length (%lu vs %lu)",
+			    sha1_to_hex(trg_entry->sha1), sz, trg_size);
+	}
+	if (!src->data) {
+		src->data = read_sha1_file(src_entry->sha1, type, &sz);
+		if (sz != src_size)
+			die("object %s inconsistent object length (%lu vs %lu)",
+			    sha1_to_hex(src_entry->sha1), sz, src_size);
+	}
+	if (!src->index) {
+		src->index = create_delta_index(src->data, src_size);
+		if (!src->index)
+			die("out of memory");
+	}
+
+	delta_buf = create_delta(src->index, trg->data, trg_size, &delta_size, max_size);
+	if (!delta_buf)
+		return 0;
+
+	trg_entry->delta = src_entry;
+	trg_entry->delta_size = delta_size;
+	trg_entry->depth = src_entry->depth + 1;
+	free(delta_buf);
+	return 1;
+}
+
+static void progress_interval(int signum)
+{
+	progress_update = 1;
+}
+
+static void find_deltas(struct object_entry **list, int window, int depth)
+{
+	int i, idx;
+	unsigned int array_size = window * sizeof(struct unpacked);
+	struct unpacked *array = xmalloc(array_size);
+	unsigned processed = 0;
+	unsigned last_percent = 999;
+
+	memset(array, 0, array_size);
+	i = nr_objects;
+	idx = 0;
+	if (progress)
+		fprintf(stderr, "Deltifying %d objects.\n", nr_result);
+
+	while (--i >= 0) {
+		struct object_entry *entry = list[i];
+		struct unpacked *n = array + idx;
+		int j;
+
+		if (!entry->preferred_base)
+			processed++;
+
+		if (progress) {
+			unsigned percent = processed * 100 / nr_result;
+			if (percent != last_percent || progress_update) {
+				fprintf(stderr, "%4u%% (%u/%u) done\r",
+					percent, processed, nr_result);
+				progress_update = 0;
+				last_percent = percent;
+			}
+		}
+
+		if (entry->delta)
+			/* This happens if we decided to reuse existing
+			 * delta from a pack.  "!no_reuse_delta &&" is implied.
+			 */
+			continue;
+
+		if (entry->size < 50)
+			continue;
+		free_delta_index(n->index);
+		n->index = NULL;
+		free(n->data);
+		n->data = NULL;
+		n->entry = entry;
+
+		j = window;
+		while (--j > 0) {
+			unsigned int other_idx = idx + j;
+			struct unpacked *m;
+			if (other_idx >= window)
+				other_idx -= window;
+			m = array + other_idx;
+			if (!m->entry)
+				break;
+			if (try_delta(n, m, depth) < 0)
+				break;
+		}
+		/* if we made n a delta, and if n is already at max
+		 * depth, leaving it in the window is pointless.  we
+		 * should evict it first.
+		 */
+		if (entry->delta && depth <= entry->depth)
+			continue;
+
+		idx++;
+		if (idx >= window)
+			idx = 0;
+	}
+
+	if (progress)
+		fputc('\n', stderr);
+
+	for (i = 0; i < window; ++i) {
+		free_delta_index(array[i].index);
+		free(array[i].data);
+	}
+	free(array);
+}
+
+static void prepare_pack(int window, int depth)
+{
+	get_object_details();
+	sorted_by_type = create_sorted_list(type_size_sort);
+	if (window && depth)
+		find_deltas(sorted_by_type, window+1, depth);
+}
+
+static int reuse_cached_pack(unsigned char *sha1, int pack_to_stdout)
+{
+	static const char cache[] = "pack-cache/pack-%s.%s";
+	char *cached_pack, *cached_idx;
+	int ifd, ofd, ifd_ix = -1;
+
+	cached_pack = git_path(cache, sha1_to_hex(sha1), "pack");
+	ifd = open(cached_pack, O_RDONLY);
+	if (ifd < 0)
+		return 0;
+
+	if (!pack_to_stdout) {
+		cached_idx = git_path(cache, sha1_to_hex(sha1), "idx");
+		ifd_ix = open(cached_idx, O_RDONLY);
+		if (ifd_ix < 0) {
+			close(ifd);
+			return 0;
+		}
+	}
+
+	if (progress)
+		fprintf(stderr, "Reusing %d objects pack %s\n", nr_objects,
+			sha1_to_hex(sha1));
+
+	if (pack_to_stdout) {
+		if (copy_fd(ifd, 1))
+			exit(1);
+		close(ifd);
+	}
+	else {
+		char name[PATH_MAX];
+		snprintf(name, sizeof(name),
+			 "%s-%s.%s", base_name, sha1_to_hex(sha1), "pack");
+		ofd = open(name, O_CREAT | O_EXCL | O_WRONLY, 0666);
+		if (ofd < 0)
+			die("unable to open %s (%s)", name, strerror(errno));
+		if (copy_fd(ifd, ofd))
+			exit(1);
+		close(ifd);
+
+		snprintf(name, sizeof(name),
+			 "%s-%s.%s", base_name, sha1_to_hex(sha1), "idx");
+		ofd = open(name, O_CREAT | O_EXCL | O_WRONLY, 0666);
+		if (ofd < 0)
+			die("unable to open %s (%s)", name, strerror(errno));
+		if (copy_fd(ifd_ix, ofd))
+			exit(1);
+		close(ifd_ix);
+		puts(sha1_to_hex(sha1));
+	}
+
+	return 1;
+}
+
+static void setup_progress_signal(void)
+{
+	struct sigaction sa;
+	struct itimerval v;
+
+	memset(&sa, 0, sizeof(sa));
+	sa.sa_handler = progress_interval;
+	sigemptyset(&sa.sa_mask);
+	sa.sa_flags = SA_RESTART;
+	sigaction(SIGALRM, &sa, NULL);
+
+	v.it_interval.tv_sec = 1;
+	v.it_interval.tv_usec = 0;
+	v.it_value = v.it_interval;
+	setitimer(ITIMER_REAL, &v, NULL);
+}
+
+static int git_pack_config(const char *k, const char *v)
+{
+	if(!strcmp(k, "pack.window")) {
+		window = git_config_int(k, v);
+		return 0;
+	}
+	return git_default_config(k, v);
+}
+
+int cmd_pack_objects(int argc, const char **argv, const char *prefix)
+{
+	SHA_CTX ctx;
+	char line[40 + 1 + PATH_MAX + 2];
+	int depth = 10, pack_to_stdout = 0;
+	struct object_entry **list;
+	int num_preferred_base = 0;
+	int i;
+
+	git_config(git_pack_config);
+
+	progress = isatty(2);
+	for (i = 1; i < argc; i++) {
+		const char *arg = argv[i];
+
+		if (*arg == '-') {
+			if (!strcmp("--non-empty", arg)) {
+				non_empty = 1;
+				continue;
+			}
+			if (!strcmp("--local", arg)) {
+				local = 1;
+				continue;
+			}
+			if (!strcmp("--progress", arg)) {
+				progress = 1;
+				continue;
+			}
+			if (!strcmp("--incremental", arg)) {
+				incremental = 1;
+				continue;
+			}
+			if (!strncmp("--window=", arg, 9)) {
+				char *end;
+				window = strtoul(arg+9, &end, 0);
+				if (!arg[9] || *end)
+					usage(pack_usage);
+				continue;
+			}
+			if (!strncmp("--depth=", arg, 8)) {
+				char *end;
+				depth = strtoul(arg+8, &end, 0);
+				if (!arg[8] || *end)
+					usage(pack_usage);
+				continue;
+			}
+			if (!strcmp("--progress", arg)) {
+				progress = 1;
+				continue;
+			}
+			if (!strcmp("-q", arg)) {
+				progress = 0;
+				continue;
+			}
+			if (!strcmp("--no-reuse-delta", arg)) {
+				no_reuse_delta = 1;
+				continue;
+			}
+			if (!strcmp("--stdout", arg)) {
+				pack_to_stdout = 1;
+				continue;
+			}
+			usage(pack_usage);
+		}
+		if (base_name)
+			usage(pack_usage);
+		base_name = arg;
+	}
+
+	if (pack_to_stdout != !base_name)
+		usage(pack_usage);
+
+	prepare_packed_git();
+
+	if (progress) {
+		fprintf(stderr, "Generating pack...\n");
+		setup_progress_signal();
+	}
+
+	for (;;) {
+		unsigned char sha1[20];
+		unsigned hash;
+
+		if (!fgets(line, sizeof(line), stdin)) {
+			if (feof(stdin))
+				break;
+			if (!ferror(stdin))
+				die("fgets returned NULL, not EOF, not error!");
+			if (errno != EINTR)
+				die("fgets: %s", strerror(errno));
+			clearerr(stdin);
+			continue;
+		}
+
+		if (line[0] == '-') {
+			if (get_sha1_hex(line+1, sha1))
+				die("expected edge sha1, got garbage:\n %s",
+				    line+1);
+			if (num_preferred_base++ < window)
+				add_preferred_base(sha1);
+			continue;
+		}
+		if (get_sha1_hex(line, sha1))
+			die("expected sha1, got garbage:\n %s", line);
+		hash = name_hash(line+41);
+		add_preferred_base_object(line+41, hash);
+		add_object_entry(sha1, hash, 0);
+	}
+	if (progress)
+		fprintf(stderr, "Done counting %d objects.\n", nr_objects);
+	sorted_by_sha = create_final_object_list();
+	if (non_empty && !nr_result)
+		return 0;
+
+	SHA1_Init(&ctx);
+	list = sorted_by_sha;
+	for (i = 0; i < nr_result; i++) {
+		struct object_entry *entry = *list++;
+		SHA1_Update(&ctx, entry->sha1, 20);
+	}
+	SHA1_Final(object_list_sha1, &ctx);
+	if (progress && (nr_objects != nr_result))
+		fprintf(stderr, "Result has %d objects.\n", nr_result);
+
+	if (reuse_cached_pack(object_list_sha1, pack_to_stdout))
+		;
+	else {
+		if (nr_result)
+			prepare_pack(window, depth);
+		if (progress && pack_to_stdout) {
+			/* the other end usually displays progress itself */
+			struct itimerval v = {{0,},};
+			setitimer(ITIMER_REAL, &v, NULL);
+			signal(SIGALRM, SIG_IGN );
+			progress_update = 0;
+		}
+		write_pack_file();
+		if (!pack_to_stdout) {
+			write_index_file();
+			puts(sha1_to_hex(object_list_sha1));
+		}
+	}
+	if (progress)
+		fprintf(stderr, "Total %d, written %d (delta %d), reused %d (delta %d)\n",
+			nr_result, written, written_delta, reused, reused_delta);
+	return 0;
+}