Merge branches 'jc/fix-co-candy', 'jc/fix-rename-leak' and 'ar/fix-win' into maint
[git.git] / pack-objects.c
index d9328a9..8f352aa 100644 (file)
 #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;
 }