Merge branch 'pj/portable' into next
[gitweb.git] / pack-objects.c
index feee5600b9c362ad1436db64e3624f646f064fc3..ceb107f63fad491423da8795360331ae0825597a 100644 (file)
-#include <ctype.h>
 #include "cache.h"
 #include "object.h"
 #include "delta.h"
 #include "pack.h"
 #include "csum-file.h"
+#include "diff.h"
+#include <sys/time.h>
 
-static const char pack_usage[] = "git-pack-objects [--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;
+
+/*
+ * 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 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)
 {
@@ -34,7 +202,7 @@ 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(otherbuf, othersize,
-                              buf, size, &delta_size, ~0UL);
+                              buf, size, &delta_size, 0);
         if (!delta_buf || delta_size != entry->delta_size)
                die("delta size changed");
         free(buf);
@@ -51,70 +219,95 @@ static void *delta_against(void *buf, unsigned long size, struct object_entry *e
  */
 static int encode_header(enum object_type type, unsigned long size, unsigned char *hdr)
 {
-       int n = 1, i;
+       int n = 1;
        unsigned char c;
 
        if (type < OBJ_COMMIT || type > OBJ_DELTA)
                die("bad type %d", type);
 
-       /*
-        * Shift the size up by 7 bits at a time,
-        * until you get bits in the "high four".
-        * That will be our beginning. We'll have
-        * four size bits in 28..31, then groups
-        * of seven in 21..27, 14..20, 7..13 and
-        * finally 0..6.
-        */
-       if (size) {
-               n = 5;
-               while (!(size & 0xfe000000)) {
-                       size <<= 7;
-                       n--;
-               }
-       }
-       c = (type << 4) | (size >> 28);
-       for (i = 1; i < n; i++) {
+       c = (type << 4) | (size & 15);
+       size >>= 4;
+       while (size) {
                *hdr++ = c | 0x80;
-               c = (size >> 21) & 0x7f;
-               size <<= 7;
+               c = size & 0x7f;
+               size >>= 7;
+               n++;
        }
        *hdr = c;
        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;
+       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);
        }
-       hdrlen = encode_header(obj_type, size, header);
-       sha1write(f, header, hdrlen);
-       if (entry->delta) {
-               sha1write(f, entry->delta, 20);
-               hdrlen += 20;
+       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++;
        }
-       datalen = sha1write_compressed(f, buf, size);
-       free(buf);
+       if (obj_type == OBJ_DELTA)
+               written_delta++;
+       written++;
        return hdrlen + datalen;
 }
 
@@ -129,7 +322,7 @@ static unsigned long write_one(struct sha1file *f,
                return offset;
        e->offset = offset;
        offset += write_object(f, e);
-       /* if we are delitified, write out its base object. */
+       /* if we are deltified, write out its base object. */
        if (e->delta)
                offset = write_one(f, e->delta, offset);
        return offset;
@@ -140,32 +333,31 @@ static void write_pack_file(void)
        int i;
        struct sha1file *f;
        unsigned long offset;
-       unsigned long mb;
        struct pack_header hdr;
 
        if (!base_name)
                f = sha1fd(1, "<stdout>");
        else
-               f = sha1create("%s.%s", base_name, "pack");
+               f = sha1create("%s-%s.%s", base_name,
+                              sha1_to_hex(object_list_sha1), "pack");
        hdr.hdr_signature = htonl(PACK_SIGNATURE);
-       hdr.hdr_version = htonl(1);
-       hdr.hdr_entries = htonl(nr_objects);
+       hdr.hdr_version = htonl(PACK_VERSION);
+       hdr.hdr_entries = htonl(nr_result);
        sha1write(f, &hdr, sizeof(hdr));
        offset = sizeof(hdr);
        for (i = 0; i < nr_objects; i++)
                offset = write_one(f, objects + i, offset);
 
        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", base_name, "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];
 
        /*
@@ -190,7 +382,7 @@ 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);
@@ -200,10 +392,87 @@ static void write_index_file(void)
        sha1close(f, NULL, 1);
 }
 
-static void 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;
+       }
+}
+
+static int add_object_entry(const unsigned char *sha1, const char *name, int exclude)
 {
+       unsigned int hash = 0;
        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;
+
+       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;
+
+       while (*name) {
+               unsigned char c = *name++;
+               if (isspace(c))
+                       continue;
+               hash = hash * 11 + c;
+       }
 
        if (idx >= nr_alloc) {
                unsigned int needed = (idx + 1024) * 3 / 2;
@@ -211,41 +480,161 @@ static void 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;
+
+       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;
+       }
+
+ already_added:
+       if (exclude)
+               entry->preferred_base = 1;
+       else {
+               if (found_pack) {
+                       entry->in_pack = found_pack;
+                       entry->in_pack_offset = found_offset;
+               }
+       }
+       return 1;
+}
+
+static void add_pbase_tree(struct tree_desc *tree)
+{
+       while (tree->size) {
+               const unsigned char *sha1;
+               const char *name;
+               unsigned mode;
+               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;
+               add_object_entry(sha1, name, 1);
+               if (!strcmp(type, "tree")) {
+                       struct tree_desc sub;
+                       void *elem;
+                       elem = read_sha1_file(sha1, type, &sub.size);
+                       sub.buf = elem;
+                       if (sub.buf) {
+                               add_pbase_tree(&sub);
+                               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;
+       add_object_entry(sha1, "", 1);
+       add_pbase_tree(&tree);
+       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);
+       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 *);
@@ -276,6 +665,24 @@ 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()
+{
+       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)
@@ -286,6 +693,10 @@ 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)
@@ -310,6 +721,8 @@ 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;
@@ -318,6 +731,22 @@ static int try_delta(struct unpacked *cur, struct unpacked *old, unsigned max_de
        if (cur_entry->type != old_entry->type)
                return -1;
 
+       /* 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;
        if (size < 50)
                return -1;
@@ -336,8 +765,27 @@ 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 0;
+               }
+               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,
@@ -347,6 +795,7 @@ 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;
 }
@@ -356,10 +805,13 @@ 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;
 
        memset(array, 0, array_size);
        i = nr_objects;
        idx = 0;
+       eye_candy = i - (nr_objects / 20);
+
        while (--i >= 0) {
                struct object_entry *entry = list[i];
                struct unpacked *n = array + idx;
@@ -367,11 +819,23 @@ 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->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;
@@ -388,18 +852,112 @@ static void find_deltas(struct object_entry **list, int window, int depth)
                if (idx >= window)
                        idx = 0;
        }
+
+       for (i = 0; i < window; ++i)
+               free(array[i].data);
+       free(array);
+}
+
+static void prepare_pack(int window, int depth)
+{
+       if (progress)
+               fprintf(stderr, "Packing %d objects", nr_result);
+       get_object_details();
+       if (progress)
+               fputc('.', stderr);
+
+       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)
+{
+       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)
 {
+       SHA_CTX ctx;
        char line[PATH_MAX + 20];
        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();
 
        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;
                                window = strtoul(arg+9, &end, 0);
@@ -414,6 +972,14 @@ int main(int argc, char **argv)
                                        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;
@@ -428,34 +994,68 @@ int main(int argc, char **argv)
        if (pack_to_stdout != !base_name)
                usage(pack_usage);
 
+       prepare_packed_git();
+       if (progress) {
+               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 (get_sha1_hex(line, sha1))
-                       die("expected sha1, got garbage");
-               hash = 0;
-               p = line+40;
-               while (*p) {
-                       unsigned char c = *p++;
-                       if (isspace(c))
-                               continue;
-                       hash = hash * 11 + c;
+               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;
                }
-               add_object_entry(sha1, hash);
+               if (get_sha1_hex(line, sha1))
+                       die("expected sha1, got garbage:\n %s", line);
+               add_object_entry(sha1, line+40, 0);
        }
-       get_object_details();
-
-       fprintf(stderr, "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 (window && depth)
-               find_deltas(sorted_by_type, window+1, depth);
+       sorted_by_sha = create_final_object_list();
+       SHA1_Init(&ctx);
+       list = sorted_by_sha;
+       for (i = 0; i < nr_result; i++) {
+               struct object_entry *entry = *list++;
+               SHA1_Update(&ctx, entry->sha1, 20);
+       }
+       SHA1_Final(object_list_sha1, &ctx);
+       if (progress && (nr_objects != nr_result))
+               fprintf(stderr, "Result has %d objects.\n", nr_result);
 
-       write_pack_file();
-       if (!pack_to_stdout)
-               write_index_file();
+       if (reuse_cached_pack(object_list_sha1, pack_to_stdout))
+               ;
+       else {
+               prepare_pack(window, depth);
+               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;
 }