X-Git-Url: https://git.octo.it/?a=blobdiff_plain;f=pack-objects.c;h=8f352aa6c1c99e7bebc7680909c9139c7a6cf623;hb=7bd1527d2d8c80a6e9a0f8583082a5aee5428c68;hp=d9328a98d8f349b75fc5ab8302b66116317781ec;hpb=75c42d8cc3b42e4b82946848b8ba902b4bbcc38d;p=git.git

diff --git a/pack-objects.c b/pack-objects.c
index d9328a98..8f352aa6 100644
--- a/pack-objects.c
+++ b/pack-objects.c
@@ -1,77 +1,189 @@
 #include "cache.h"
 #include "object.h"
 #include "delta.h"
+#include "pack.h"
+#include "csum-file.h"
+#include <sys/time.h>
+#include <signal.h>
 
-static const char pack_usage[] = "git-pack-objects [--window=N] base-name < object-list";
-
-enum object_type {
-	OBJ_NONE,
-	OBJ_COMMIT,
-	OBJ_TREE,
-	OBJ_BLOB,
-	OBJ_DELTA	// NOTE! This is _not_ the same as a "delta" object in the filesystem
-};
+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;
-	unsigned long offset;
-	unsigned int depth;
-	unsigned int flags;
+	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;
-	unsigned long delta_size;
-	struct object_entry *delta;
+	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; /* delitified objects who bases me */
+	struct object_entry *delta_sibling; /* other deltified objects who
+					     * uses the same base as me
+					     */
 };
 
+/*
+ * Objects we are going to pack are colected 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;
-static int delta_window = 10;
 static const char *base_name;
+static unsigned char pack_file_sha1[20];
+static int progress = 1;
+static volatile int progress_update = 0;
 
-struct myfile {
-	int fd;
-	unsigned long chars;
-	unsigned char buffer[8192];
-};
+/*
+ * 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 int ui = (unsigned int) 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 FILE *create_file(const char *suffix)
+static void prepare_pack_ix(void)
 {
-	static char filename[PATH_MAX];
-	unsigned len;
+	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 */
+}
 
-	len = snprintf(filename, PATH_MAX, "%s.%s", base_name, suffix);
-	if (len >= PATH_MAX)
-		die("you wascally wabbit, you");
-	return fopen(filename, "w");
+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;
 }
 
-static unsigned long fwrite_compressed(void *in, unsigned long size, FILE *f)
+/*
+ * Ordered list of offsets of objects in the pack.
+ */
+static void prepare_pack_revindex(struct pack_revindex *rix)
 {
-	z_stream stream;
-	unsigned long maxsize;
-	void *out;
-
-	memset(&stream, 0, sizeof(stream));
-	deflateInit(&stream, Z_DEFAULT_COMPRESSION);
-	maxsize = deflateBound(&stream, size);
-	out = xmalloc(maxsize);
-
-	/* Compress it */
-	stream.next_in = in;
-	stream.avail_in = size;
-
-	stream.next_out = out;
-	stream.avail_out = maxsize;
-
-	while (deflate(&stream, Z_FINISH) == Z_OK)
-		/* nothing */;
-	deflateEnd(&stream);
-
-	size = stream.total_out;
-	fwrite(out, size, 1, f);
-	free(out);
-	return size;
+	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++) {
+		long hl = *((long *)(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)
@@ -83,7 +195,8 @@ static void *delta_against(void *buf, unsigned long size, struct object_entry *e
 
 	if (!otherbuf)
 		die("unable to read %s", sha1_to_hex(entry->delta->sha1));
-        delta_buf = diff_delta(buf, size, otherbuf, othersize, &delta_size, ~0UL);
+        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);
@@ -91,62 +204,166 @@ static void *delta_against(void *buf, unsigned long size, struct object_entry *e
 	return delta_buf;
 }
 
-static unsigned long write_object(FILE *f, struct object_entry *entry)
+/*
+ * 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 = read_sha1_file(entry->sha1, type, &size);
-	char header[21];
+	void *buf;
+	unsigned char header[10];
 	unsigned hdrlen, datalen;
-
-	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);
-
-	/*
-	 * The object header is a byte of 'type' followed by four bytes of
-	 * length, except for deltas that has the 20 bytes of delta sha
-	 * instead.
-	 */
-	header[0] = ".CTB"[entry->type];
-	datalen = htonl(size);
-	memcpy(header+1, &datalen, 4);
-	hdrlen = 5;
-	if (entry->delta) {
-		header[0] = 'D';
-		memcpy(header+1, entry->delta, 20);
-		buf = delta_against(buf, size, entry);
-		size = entry->delta_size;
-		hdrlen = 21;
+	enum object_type obj_type;
+	int to_reuse = 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);
 	}
-	fwrite(header, hdrlen, 1, f);
-	datalen = fwrite_compressed(buf, size, f);
-	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 = 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;
-	FILE *f = create_file("pack");
-	unsigned long offset = 0;
-	unsigned long mb;
+	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_objects);
+
+	hdr.hdr_signature = htonl(PACK_SIGNATURE);
+	hdr.hdr_version = htonl(PACK_VERSION);
+	hdr.hdr_entries = htonl(nr_objects);
+	sha1write(f, &hdr, sizeof(hdr));
+	offset = sizeof(hdr);
 	for (i = 0; i < nr_objects; i++) {
-		struct object_entry *entry = objects + i;
-		entry->offset = offset;
-		offset += write_object(f, entry);
+		offset = write_one(f, objects + i, offset);
+		if (do_progress) {
+			unsigned percent = written * 100 / nr_objects;
+			if (progress_update || percent != last_percent) {
+				fprintf(stderr, "%4u%% (%u/%u) done\r",
+					percent, written, nr_objects);
+				progress_update = 0;
+				last_percent = percent;
+			}
+		}
 	}
-	fclose(f);
-	mb = offset >> 20;
-	offset &= 0xfffff;
+	if (do_progress)
+		fputc('\n', stderr);
+
+	sha1close(f, pack_file_sha1, 1);
 }
 
 static void write_index_file(void)
 {
 	int i;
-	FILE *f = create_file("idx");
+	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_objects;
 	unsigned int array[256];
@@ -154,7 +371,7 @@ static void write_index_file(void)
 	/*
 	 * 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)
+	 * having to do eight extra binary search iterations).
 	 */
 	for (i = 0; i < 256; i++) {
 		struct object_entry **next = list;
@@ -167,7 +384,7 @@ static void write_index_file(void)
 		array[i] = htonl(next - sorted_by_sha);
 		list = next;
 	}
-	fwrite(array, 256, sizeof(int), f);
+	sha1write(f, array, 256 * sizeof(int));
 
 	/*
 	 * Write the actual SHA1 entries..
@@ -176,16 +393,34 @@ static void write_index_file(void)
 	for (i = 0; i < nr_objects; i++) {
 		struct object_entry *entry = *list++;
 		unsigned int offset = htonl(entry->offset);
-		fwrite(&offset, 4, 1, f);
-		fwrite(entry->sha1, 20, 1, f);
+		sha1write(f, &offset, 4);
+		sha1write(f, entry->sha1, 20);
 	}
-	fclose(f);
+	sha1write(f, pack_file_sha1, 20);
+	sha1close(f, NULL, 1);
 }
 
-static void add_object_entry(unsigned char *sha1)
+static int add_object_entry(unsigned char *sha1, unsigned int hash)
 {
 	unsigned int idx = nr_objects;
 	struct object_entry *entry;
+	struct packed_git *p;
+	unsigned int found_offset = 0;
+	struct packed_git *found_pack = NULL;
+
+	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 (idx >= nr_alloc) {
 		unsigned int needed = (idx + 1024) * 3 / 2;
@@ -195,42 +430,144 @@ static void add_object_entry(unsigned char *sha1)
 	entry = objects + idx;
 	memset(entry, 0, sizeof(*entry));
 	memcpy(entry->sha1, sha1, 20);
+	entry->hash = hash;
+	if (found_pack) {
+		entry->in_pack = found_pack;
+		entry->in_pack_offset = found_offset;
+	}
 	nr_objects = idx+1;
+	return 1;
+}
+
+static int locate_object_entry_hash(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(unsigned char *sha1)
+{
+	int i = locate_object_entry_hash(sha1);
+	if (0 <= i)
+		return &objects[object_ix[i]-1];
+	return NULL;
 }
 
 static void check_object(struct object_entry *entry)
 {
-	char buffer[128];
-	char type[10];
-	unsigned long mapsize;
-	z_stream stream;
-	void *map;
-
-	map = map_sha1_file(entry->sha1, &mapsize);
-	if (!map)
-		die("unable to map %s", sha1_to_hex(entry->sha1));
-	if (unpack_sha1_header(&stream, map, mapsize, buffer, sizeof(buffer)) < 0)
-		die("unable to unpack %s header", sha1_to_hex(entry->sha1));
-	munmap(map, mapsize);
-	if (parse_sha1_header(buffer, type, &entry->size) < 0)
-		die("unable to parse %s header", sha1_to_hex(entry->sha1));
+	char type[20];
+
+	if (entry->in_pack) {
+		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))) {
+
+			/* 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")) {
 		entry->type = OBJ_COMMIT;
 	} else if (!strcmp(type, "tree")) {
 		entry->type = OBJ_TREE;
 	} else if (!strcmp(type, "blob")) {
 		entry->type = OBJ_BLOB;
+	} else if (!strcmp(type, "tag")) {
+		entry->type = OBJ_TAG;
 	} else
-		die("unable to pack object %s of type %s", sha1_to_hex(entry->sha1), type);
+		die("unable to pack object %s of type %s",
+		    sha1_to_hex(entry->sha1), type);
+}
+
+static void hash_objects(void)
+{
+	int i;
+	struct object_entry *oe;
+
+	object_ix_hashsz = nr_objects * 2;
+	object_ix = xcalloc(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) {
+			error("the same object '%s' added twice",
+			      sha1_to_hex(oe->sha1));
+			continue;
+		}
+		ix = -1 - ix;
+		object_ix[ix] = i + 1;
+	}
+}
+
+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 = objects;
+	struct object_entry *entry;
 
-	for (i = 0; i < nr_objects; i++)
-		check_object(entry++);
+	hash_objects();
+	prepare_pack_ix();
+	for (i = 0, entry = objects; i < nr_objects; i++, entry++)
+		check_object(entry);
+	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 *);
@@ -267,6 +604,10 @@ static int type_size_sort(const struct object_entry *a, const struct object_entr
 		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->size < b->size)
 		return -1;
 	if (a->size > b->size)
@@ -280,18 +621,18 @@ struct unpacked {
 };
 
 /*
- * We search for deltas in a list sorted by type and by size, and
- * walk the "old" chain backwards in the list, so if the type
- * has changed or the size difference is too big, there's no point
- * in even continuing the walk, since the other old objects are
- * going to be even smaller or of a different type. So return -1
- * once we determine that there's no point even trying.
+ * 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 *cur, struct unpacked *old)
+static int try_delta(struct unpacked *cur, struct unpacked *old, unsigned max_depth)
 {
 	struct object_entry *cur_entry = cur->entry;
 	struct object_entry *old_entry = old->entry;
-	unsigned long size, oldsize, delta_size;
+	unsigned long size, oldsize, delta_size, sizediff;
 	long max_size;
 	void *delta_buf;
 
@@ -299,13 +640,25 @@ static int try_delta(struct unpacked *cur, struct unpacked *old)
 	if (cur_entry->type != old_entry->type)
 		return -1;
 
-	/* Size is guaranteed to be larger than or equal to oldsize */
+	/* If the current object is at edge, take the depth the objects
+	 * that depend on the current object into account -- otherwise
+	 * they would become too deep.
+	 */
+	if (cur_entry->delta_child) {
+		if (max_depth <= cur_entry->delta_limit)
+			return 0;
+		max_depth -= cur_entry->delta_limit;
+	}
+
 	size = cur_entry->size;
 	if (size < 50)
 		return -1;
 	oldsize = old_entry->size;
-	if (size - oldsize > oldsize / 4)
+	sizediff = oldsize > size ? oldsize - size : size - oldsize;
+	if (sizediff > size / 8)
 		return -1;
+	if (old_entry->depth >= max_depth)
+		return 0;
 
 	/*
 	 * NOTE!
@@ -317,35 +670,69 @@ static int try_delta(struct unpacked *cur, struct unpacked *old)
 	max_size = size / 2 - 20;
 	if (cur_entry->delta)
 		max_size = cur_entry->delta_size-1;
-	delta_buf = diff_delta(cur->data, size, old->data, oldsize, &delta_size, max_size);
+	if (sizediff >= max_size)
+		return -1;
+	delta_buf = diff_delta(old->data, oldsize,
+			       cur->data, size, &delta_size, max_size);
 	if (!delta_buf)
 		return 0;
 	cur_entry->delta = old_entry;
 	cur_entry->delta_size = delta_size;
+	cur_entry->depth = old_entry->depth + 1;
 	free(delta_buf);
 	return 0;
 }
 
-static void find_deltas(struct object_entry **list, int window)
+static void progress_interval(int signum)
 {
-	unsigned int i;
+	signal(SIGALRM, progress_interval);
+	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);
-	for (i = 0; i < nr_objects; i++) {
-		unsigned int idx = i % window;
+	i = nr_objects;
+	idx = 0;
+	if (progress)
+		fprintf(stderr, "Deltifying %d objects.\n", nr_objects);
+
+	while (--i >= 0) {
 		struct object_entry *entry = list[i];
 		struct unpacked *n = array + idx;
 		unsigned long size;
 		char type[10];
 		int j;
 
+		processed++;
+		if (progress) {
+			unsigned percent = processed * 100 / nr_objects;
+			if (percent != last_percent || progress_update) {
+				fprintf(stderr, "%4u%% (%u/%u) done\r",
+					percent, processed, nr_objects);
+				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;
+
 		free(n->data);
 		n->entry = entry;
 		n->data = read_sha1_file(entry->sha1, type, &size);
 		if (size != entry->size)
 			die("object %s inconsistent object length (%lu vs %lu)", sha1_to_hex(entry->sha1), size, entry->size);
+
 		j = window;
 		while (--j > 0) {
 			unsigned int other_idx = idx + j;
@@ -355,28 +742,136 @@ static void find_deltas(struct object_entry **list, int window)
 			m = array + other_idx;
 			if (!m->entry)
 				break;
-			if (try_delta(n, m) < 0)
+			if (try_delta(n, m, depth) < 0)
 				break;
 		}
+		idx++;
+		if (idx >= window)
+			idx = 0;
 	}
+
+	if (progress)
+		fputc('\n', stderr);
+
+	for (i = 0; i < window; ++i)
+		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;
 }
 
 int main(int argc, char **argv)
 {
-	char line[128];
+	SHA_CTX ctx;
+	char line[PATH_MAX + 20];
+	int window = 10, depth = 10, pack_to_stdout = 0;
+	struct object_entry **list;
 	int i;
 
+	setup_git_directory();
+
 	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("--incremental", arg)) {
+				incremental = 1;
+				continue;
+			}
 			if (!strncmp("--window=", arg, 9)) {
 				char *end;
-				delta_window = strtoul(arg+9, &end, 0);
+				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("-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)
@@ -384,25 +879,75 @@ int main(int argc, char **argv)
 		base_name = arg;
 	}
 
-	if (!base_name)
+	if (pack_to_stdout != !base_name)
 		usage(pack_usage);
 
+	prepare_packed_git();
+
+	if (progress) {
+		struct itimerval v;
+		v.it_interval.tv_sec = 1;
+		v.it_interval.tv_usec = 0;
+		v.it_value = v.it_interval;
+		signal(SIGALRM, progress_interval);
+		setitimer(ITIMER_REAL, &v, NULL);
+		fprintf(stderr, "Generating pack...\n");
+	}
+
 	while (fgets(line, sizeof(line), stdin) != NULL) {
+		unsigned int hash;
+		char *p;
 		unsigned char sha1[20];
+
+		if (progress_update) {
+			fprintf(stderr, "Counting objects...%d\r", nr_objects);
+			progress_update = 0;
+		}
 		if (get_sha1_hex(line, sha1))
-			die("expected sha1, got garbage");
-		add_object_entry(sha1);
+			die("expected sha1, got garbage:\n %s", line);
+		hash = 0;
+		p = line+40;
+		while (*p) {
+			unsigned char c = *p++;
+			if (isspace(c))
+				continue;
+			hash = hash * 11 + c;
+		}
+		add_object_entry(sha1, hash);
 	}
-	get_object_details();
-
-	printf("Packing %d objects\n", nr_objects);
+	if (progress)
+		fprintf(stderr, "Done counting %d objects.\n", nr_objects);
+	if (non_empty && !nr_objects)
+		return 0;
 
 	sorted_by_sha = create_sorted_list(sha1_sort);
-	sorted_by_type = create_sorted_list(type_size_sort);
-	if (delta_window)
-		find_deltas(sorted_by_type, delta_window);
-
-	write_pack_file();
-	write_index_file();
+	SHA1_Init(&ctx);
+	list = sorted_by_sha;
+	for (i = 0; i < nr_objects; i++) {
+		struct object_entry *entry = *list++;
+		SHA1_Update(&ctx, entry->sha1, 20);
+	}
+	SHA1_Final(object_list_sha1, &ctx);
+
+	if (reuse_cached_pack(object_list_sha1, pack_to_stdout))
+		;
+	else {
+		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_objects, written, written_delta, reused, reused_delta);
 	return 0;
 }