Merge part of 'lt/rev-list' into 'fk/blame'

Now blame will depend on the new revision walker infrastructure,
we need to make it depend on earlier parts of Linus' rev-list
topic branch, hence this merge.

Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 686 insertions, 119 deletions

diff --git a/pack-objects.c b/pack-objects.c
index c5a5e61605..21ee572f48 100644
--- a/pack-objects.c
+++ b/pack-objects.c
@@ -3,31 +3,196 @@
 #include "delta.h"
 #include "pack.h"
 #include "csum-file.h"
+#include "diff.h"
 #include <sys/time.h>
+#include <signal.h>
 
-static const char pack_usage[] = "git-pack-objects [-q] [--non-empty] [--local] [--incremental] [--window=N] [--depth=N] {--stdout | base-name} < object-list";
+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 hash;
+	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
+					     */
+	int preferred_base;	/* we do not pack this, but is encouraged to
+				 * be used as the base objectto delta huge
+				 * objects against.
+				 */
+	int based_on_preferred;	/* current delta candidate is a preferred
+				 * one, or delta against a preferred one.
+				 */
 };
 
+/*
+ * 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 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 int progress_update = 0;
+
+/*
+ * 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)(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++) {
+		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)
 {
@@ -74,39 +239,77 @@ static int encode_header(enum object_type type, unsigned long size, unsigned cha
 	return n;
 }
 
-static unsigned long write_object(struct sha1file *f, struct object_entry *entry)
+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);
+	void *buf;
 	unsigned char header[10];
 	unsigned hdrlen, datalen;
 	enum object_type obj_type;
+	int to_reuse = 0;
 
-	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->preferred_base)
+		return 0;
 
-	/*
-	 * 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.
-	 */
 	obj_type = entry->type;
-	if (entry->delta) {
-		buf = delta_against(buf, size, entry);
-		size = entry->delta_size;
-		obj_type = OBJ_DELTA;
-	}
-	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);
+	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 = 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;
 }
 
@@ -132,32 +335,52 @@ static void write_pack_file(void)
 	int i;
 	struct sha1file *f;
 	unsigned long offset;
-	unsigned long mb;
 	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");
+	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_objects);
+	hdr.hdr_entries = htonl(nr_result);
 	sha1write(f, &hdr, sizeof(hdr));
 	offset = sizeof(hdr);
-	for (i = 0; i < nr_objects; i++)
+	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);
-	mb = offset >> 20;
-	offset &= 0xfffff;
 }
 
 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 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;
+	struct object_entry **last = list + nr_result;
 	unsigned int array[256];
 
 	/*
@@ -182,7 +405,7 @@ static void write_index_file(void)
 	 * Write the actual SHA1 entries..
 	 */
 	list = sorted_by_sha;
-	for (i = 0; i < nr_objects; i++) {
+	for (i = 0; i < nr_result; i++) {
 		struct object_entry *entry = *list++;
 		unsigned int offset = htonl(entry->offset);
 		sha1write(f, &offset, 4);
@@ -192,25 +415,139 @@ static void write_index_file(void)
 	sha1close(f, NULL, 1);
 }
 
-static int add_object_entry(unsigned char *sha1, unsigned int hash)
+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);
+	object_ix = 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;
+	}
+}
+
+struct name_path {
+	struct name_path *up;
+	const char *elem;
+	int len;
+};
+
+#define DIRBITS 12
+
+static unsigned name_hash(struct name_path *path, const char *name)
+{
+	struct name_path *p = path;
+	const char *n = name + strlen(name);
+	unsigned hash = 0, name_hash = 0, name_done = 0;
+
+	if (n != name && n[-1] == '\n')
+		n--;
+	while (name <= --n) {
+		unsigned char c = *n;
+		if (c == '/' && !name_done) {
+			name_hash = hash;
+			name_done = 1;
+			hash = 0;
+		}
+		hash = hash * 11 + c;
+	}
+	if (!name_done) {
+		name_hash = hash;
+		hash = 0;
+	}
+	for (p = path; p; p = p->up) {
+		hash = hash * 11 + '/';
+		n = p->elem + p->len;
+		while (p->elem <= --n) {
+			unsigned char c = *n;
+			hash = hash * 11 + c;
+		}
+	}
+	/*
+	 * Make sure "Makefile" and "t/Makefile" are hashed separately
+	 * but close enough.
+	 */
+	hash = (name_hash<<DIRBITS) | (hash & ((1U<<DIRBITS )-1));
+
+	if (0) { /* debug */
+		n = name + strlen(name);
+		if (n != name && n[-1] == '\n')
+			n--;
+		while (name <= --n)
+			fputc(*n, stderr);
+		for (p = path; p; p = p->up) {
+			fputc('/', stderr);
+			n = p->elem + p->len;
+			while (p->elem <= --n)
+				fputc(*n, stderr);
+		}
+		fprintf(stderr, "\t%08x\n", hash);
+	}
+	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 (incremental || local) {
-		struct packed_git *p;
-
+	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;
@@ -218,42 +555,189 @@ static int add_object_entry(unsigned char *sha1, unsigned int hash)
 		nr_alloc = needed;
 	}
 	entry = objects + idx;
+	nr_objects = idx + 1;
 	memset(entry, 0, sizeof(*entry));
 	memcpy(entry->sha1, sha1, 20);
 	entry->hash = hash;
-	nr_objects = idx+1;
-	return 1;
+
+	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;
+}
+
+static void add_pbase_tree(struct tree_desc *tree, struct name_path *up)
+{
+	while (tree->size) {
+		const unsigned char *sha1;
+		const char *name;
+		unsigned mode, hash;
+		unsigned long size;
+		char type[20];
+
+		sha1 = tree_entry_extract(tree, &name, &mode);
+		update_tree_entry(tree);
+		if (!has_sha1_file(sha1))
+			continue;
+		if (sha1_object_info(sha1, type, &size))
+			continue;
+
+		hash = name_hash(up, name);
+		if (!add_object_entry(sha1, hash, 1))
+			continue;
+
+		if (!strcmp(type, "tree")) {
+			struct tree_desc sub;
+			void *elem;
+			struct name_path me;
+
+			elem = read_sha1_file(sha1, type, &sub.size);
+			sub.buf = elem;
+			if (sub.buf) {
+				me.up = up;
+				me.elem = name;
+				me.len = strlen(name);
+				add_pbase_tree(&sub, &me);
+				free(elem);
+			}
+		}
+	}
+}
+
+static void add_preferred_base(unsigned char *sha1)
+{
+	struct tree_desc tree;
+	void *elem;
+
+	elem = read_object_with_reference(sha1, "tree", &tree.size, NULL);
+	tree.buf = elem;
+	if (!tree.buf)
+		return;
+	if (add_object_entry(sha1, name_hash(NULL, ""), 1))
+		add_pbase_tree(&tree, NULL);
+	free(elem);
 }
 
 static void check_object(struct object_entry *entry)
 {
 	char type[20];
 
-	if (!sha1_object_info(entry->sha1, type, &entry->size)) {
-		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);
+	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 */
 	}
-	else
+
+	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);
+}
+
+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++);
+	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 *);
@@ -284,6 +768,24 @@ 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)
@@ -294,6 +796,10 @@ static int type_size_sort(const struct object_entry *a, const struct object_entr
 		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)
@@ -318,6 +824,8 @@ static int try_delta(struct unpacked *cur, struct unpacked *old, unsigned max_de
 {
 	struct object_entry *cur_entry = cur->entry;
 	struct object_entry *old_entry = old->entry;
+	int old_preferred = (old_entry->preferred_base ||
+			     old_entry->based_on_preferred);
 	unsigned long size, oldsize, delta_size, sizediff;
 	long max_size;
 	void *delta_buf;
@@ -326,12 +834,27 @@ static int try_delta(struct unpacked *cur, struct unpacked *old, unsigned max_de
 	if (cur_entry->type != old_entry->type)
 		return -1;
 
-	size = cur_entry->size;
-	if (size < 50)
+	/* We do not compute delta to *create* objects we are not
+	 * going to pack.
+	 */
+	if (cur_entry->preferred_base)
 		return -1;
+
+	/* 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 (cur_entry->delta_child) {
+		if (max_depth <= cur_entry->delta_limit)
+			return 0;
+		max_depth -= cur_entry->delta_limit;
+	}
+
+	size = cur_entry->size;
 	oldsize = old_entry->size;
 	sizediff = oldsize > size ? oldsize - size : size - oldsize;
-	if (sizediff > size / 8)
+
+	if (size < 50)
 		return -1;
 	if (old_entry->depth >= max_depth)
 		return 0;
@@ -344,8 +867,27 @@ static int try_delta(struct unpacked *cur, struct unpacked *old, unsigned max_de
 	 * delete).
 	 */
 	max_size = size / 2 - 20;
-	if (cur_entry->delta)
-		max_size = cur_entry->delta_size-1;
+	if (cur_entry->delta) {
+		if (cur_entry->based_on_preferred) {
+			if (old_preferred)
+				max_size = cur_entry->delta_size-1;
+			else
+				/* trying with non-preferred one when we
+				 * already have a delta based on preferred
+				 * one is pointless.
+				 */
+				return -1;
+		}
+		else if (!old_preferred)
+			max_size = cur_entry->delta_size-1;
+		else
+			/* otherwise...  even if delta with a
+			 * preferred one produces a bigger result than
+			 * what we currently have, which is based on a
+			 * non-preferred one, it is OK.
+			 */
+			;
+	}
 	if (sizediff >= max_size)
 		return -1;
 	delta_buf = diff_delta(old->data, oldsize,
@@ -355,21 +897,30 @@ static int try_delta(struct unpacked *cur, struct unpacked *old, unsigned max_de
 	cur_entry->delta = old_entry;
 	cur_entry->delta_size = delta_size;
 	cur_entry->depth = old_entry->depth + 1;
+	cur_entry->based_on_preferred = old_preferred;
 	free(delta_buf);
 	return 0;
 }
 
+static void progress_interval(int signum)
+{
+	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);
-	int eye_candy;
+	unsigned processed = 0;
+	unsigned last_percent = 999;
 
 	memset(array, 0, array_size);
 	i = nr_objects;
 	idx = 0;
-	eye_candy = i - (nr_objects / 20);
+	if (progress)
+		fprintf(stderr, "Deltifying %d objects.\n", nr_result);
 
 	while (--i >= 0) {
 		struct object_entry *entry = list[i];
@@ -378,15 +929,31 @@ static void find_deltas(struct object_entry **list, int window, int depth)
 		char type[10];
 		int j;
 
-		if (progress && i <= eye_candy) {
-			eye_candy -= nr_objects / 20;
-			fputc('.', stderr);
+		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;
+
 		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;
@@ -404,6 +971,9 @@ static void find_deltas(struct object_entry **list, int window, int depth)
 			idx = 0;
 	}
 
+	if (progress)
+		fputc('\n', stderr);
+
 	for (i = 0; i < window; ++i)
 		free(array[i].data);
 	free(array);
@@ -412,15 +982,9 @@ static void find_deltas(struct object_entry **list, int window, int depth)
 static void prepare_pack(int window, int depth)
 {
 	get_object_details();
-
-	if (progress)
-		fprintf(stderr, "Packing %d objects", nr_objects);
 	sorted_by_type = create_sorted_list(type_size_sort);
 	if (window && depth)
 		find_deltas(sorted_by_type, window+1, depth);
-	if (progress)
-		fputc('\n', stderr);
-	write_pack_file();
 }
 
 static int reuse_cached_pack(unsigned char *sha1, int pack_to_stdout)
@@ -443,8 +1007,9 @@ static int reuse_cached_pack(unsigned char *sha1, int pack_to_stdout)
 		}
 	}
 
-	fprintf(stderr, "Reusing %d objects pack %s\n", nr_objects,
-		sha1_to_hex(sha1));
+	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))
@@ -483,10 +1048,6 @@ int main(int argc, char **argv)
 	int window = 10, depth = 10, pack_to_stdout = 0;
 	struct object_entry **list;
 	int i;
-	struct timeval prev_tv;
-	int eye_candy = 0;
-	int eye_candy_incr = 500;
-
 
 	setup_git_directory();
 
@@ -524,6 +1085,10 @@ int main(int argc, char **argv)
 				progress = 0;
 				continue;
 			}
+			if (!strcmp("--no-reuse-delta", arg)) {
+				no_reuse_delta = 1;
+				continue;
+			}
 			if (!strcmp("--stdout", arg)) {
 				pack_to_stdout = 1;
 				continue;
@@ -539,65 +1104,67 @@ int main(int argc, char **argv)
 		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");
-		gettimeofday(&prev_tv, NULL);
 	}
+
 	while (fgets(line, sizeof(line), stdin) != NULL) {
-		unsigned int hash;
-		char *p;
 		unsigned char sha1[20];
 
-		if (progress && (eye_candy <= nr_objects)) {
-			fprintf(stderr, "Counting objects...%d\r", nr_objects);
-			if (eye_candy && (50 <= eye_candy_incr)) {
-				struct timeval tv;
-				int time_diff;
-				gettimeofday(&tv, NULL);
-				time_diff = (tv.tv_sec - prev_tv.tv_sec);
-				time_diff <<= 10;
-				time_diff += (tv.tv_usec - prev_tv.tv_usec);
-				if ((1 << 9) < time_diff)
-					eye_candy_incr += 50;
-				else if (50 < eye_candy_incr)
-					eye_candy_incr -= 50;
-			}
-			eye_candy += eye_candy_incr;
+		if (line[0] == '-') {
+			if (get_sha1_hex(line+1, sha1))
+				die("expected edge sha1, got garbage:\n %s",
+				    line+1);
+			add_preferred_base(sha1);
+			continue;
 		}
 		if (get_sha1_hex(line, 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);
+		add_object_entry(sha1, name_hash(NULL, line+41), 0);
 	}
 	if (progress)
 		fprintf(stderr, "Done counting %d objects.\n", nr_objects);
-	if (non_empty && !nr_objects)
+	sorted_by_sha = create_final_object_list();
+	if (non_empty && !nr_result)
 		return 0;
 
-	sorted_by_sha = create_sorted_list(sha1_sort);
 	SHA1_Init(&ctx);
 	list = sorted_by_sha;
-	for (i = 0; i < nr_objects; i++) {
+	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 {
-		prepare_pack(window, depth);
+		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;
 }