Provide some technical documentation for shallow clones

[git/libgit-gsoc.git] / builtin-pack-objects.c

#include "builtin.h"
#include "cache.h"
#include "object.h"
#include "blob.h"
#include "commit.h"
#include "tag.h"
#include "tree.h"
#include "delta.h"
#include "pack.h"
#include "csum-file.h"
#include "tree-walk.h"
#include "diff.h"
#include "revision.h"
#include "list-objects.h"

static const char pack_usage[] = "\
git-pack-objects [{ -q | --progress | --all-progress }] \n\
        [--local] [--incremental] [--window=N] [--depth=N] \n\
        [--no-reuse-delta] [--delta-base-offset] [--non-empty] \n\
        [--revs [--unpacked | --all]*] [--reflog] [--stdout | base-name] \n\
        [<ref-list | <object-list]";

struct object_entry {
        unsigned char sha1[20];
        unsigned long size;     /* uncompressed size */
        off_t offset;   /* offset into the final pack file;
                                 * nonzero if already written.
                                 */
        unsigned int depth;     /* delta depth */
        unsigned int delta_limit;       /* base adjustment for in-pack delta */
        unsigned int hash;      /* name hint hash */
        enum object_type type;
        enum object_type in_pack_type;  /* could be delta */
        unsigned long delta_size;       /* delta data size (uncompressed) */
#define in_pack_header_size delta_size  /* only when reusing pack data */
        struct object_entry *delta;     /* delta base object */
        struct packed_git *in_pack;     /* already in pack */
        off_t in_pack_offset;
        struct object_entry *delta_child; /* deltified objects who bases me */
        struct object_entry *delta_sibling; /* other deltified objects who
                                             * uses the same base as me
                                             */
        int preferred_base;     /* we do not pack this, but is encouraged to
                                 * be used as the base objectto delta huge
                                 * objects against.
                                 */
};

/*
 * Objects we are going to pack are collected in objects array (dynamically
 * expanded).  nr_objects & nr_alloc controls this array.  They are stored
 * in the order we see -- typically rev-list --objects order that gives us
 * nice "minimum seek" order.
 *
 * sorted-by-sha ans sorted-by-type are arrays of pointers that point at
 * elements in the objects array.  The former is used to build the pack
 * index (lists object names in the ascending order to help offset lookup),
 * and the latter is used to group similar things together by try_delta()
 * heuristics.
 */

static unsigned char object_list_sha1[20];
static int non_empty;
static int no_reuse_delta;
static int local;
static int incremental;
static int allow_ofs_delta;

static struct object_entry **sorted_by_sha, **sorted_by_type;
static struct object_entry *objects;
static uint32_t nr_objects, nr_alloc, nr_result;
static const char *base_name;
static unsigned char pack_file_sha1[20];
static int progress = 1;
static volatile sig_atomic_t progress_update;
static int window = 10;
static int pack_to_stdout;
static int num_preferred_base;

/*
 * 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;
static int object_ix_hashsz;

/*
 * 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).  It is
 * also rather expensive to find the sha1 for an object given its offset.
 *
 * 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 a list of offset/index_nr pairs
 * ordered by offset, so if you know the offset of an object, next offset
 * is where its packed representation ends and the index_nr can be used to
 * get the object sha1 from the main index.
 */
struct revindex_entry {
        off_t offset;
        unsigned int nr;
};
struct pack_revindex {
        struct packed_git *p;
        struct revindex_entry *revindex;
};
static struct  pack_revindex *pack_revindex;
static int pack_revindex_hashsz;

/*
 * stats
 */
static uint32_t written, written_delta;
static uint32_t reused, reused_delta;

static int pack_revindex_ix(struct packed_git *p)
{
        unsigned long ui = (unsigned long)p;
        int i;

        ui = ui ^ (ui >> 16); /* defeat structure alignment */
        i = (int)(ui % pack_revindex_hashsz);
        while (pack_revindex[i].p) {
                if (pack_revindex[i].p == p)
                        return i;
                if (++i == pack_revindex_hashsz)
                        i = 0;
        }
        return -1 - i;
}

static void prepare_pack_ix(void)
{
        int num;
        struct packed_git *p;
        for (num = 0, p = packed_git; p; p = p->next)
                num++;
        if (!num)
                return;
        pack_revindex_hashsz = num * 11;
        pack_revindex = xcalloc(sizeof(*pack_revindex), pack_revindex_hashsz);
        for (p = packed_git; p; p = p->next) {
                num = pack_revindex_ix(p);
                num = - 1 - num;
                pack_revindex[num].p = p;
        }
        /* revindex elements are lazily initialized */
}

static int cmp_offset(const void *a_, const void *b_)
{
        const struct revindex_entry *a = a_;
        const struct revindex_entry *b = b_;
        return (a->offset < b->offset) ? -1 : (a->offset > b->offset) ? 1 : 0;
}

/*
 * 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;
        const char *index = p->index_data;

        index += 4 * 256;
        rix->revindex = xmalloc(sizeof(*rix->revindex) * (num_ent + 1));
        for (i = 0; i < num_ent; i++) {
                uint32_t hl = *((uint32_t *)(index + 24 * i));
                rix->revindex[i].offset = ntohl(hl);
                rix->revindex[i].nr = i;
        }
        /* This knows the pack format -- the 20-byte trailer
         * follows immediately after the last object data.
         */
        rix->revindex[num_ent].offset = p->pack_size - 20;
        rix->revindex[num_ent].nr = -1;
        qsort(rix->revindex, num_ent, sizeof(*rix->revindex), cmp_offset);
}

static struct revindex_entry * find_packed_object(struct packed_git *p,
                                                  off_t ofs)
{
        int num;
        int lo, hi;
        struct pack_revindex *rix;
        struct revindex_entry *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].offset == ofs) {
                        return revindex + mi;
                }
                else if (ofs < revindex[mi].offset)
                        hi = mi;
                else
                        lo = mi + 1;
        } while (lo < hi);
        die("internal error: pack revindex corrupt");
}

static off_t find_packed_object_size(struct packed_git *p, off_t ofs)
{
        struct revindex_entry *entry = find_packed_object(p, ofs);
        return entry[1].offset - ofs;
}

static const unsigned char *find_packed_object_name(struct packed_git *p,
                                                    off_t ofs)
{
        struct revindex_entry *entry = find_packed_object(p, ofs);
        return ((unsigned char *)p->index_data) + 4 * 256 + 24 * entry->nr + 4;
}

static void *delta_against(void *buf, unsigned long size, struct object_entry *entry)
{
        unsigned long othersize, delta_size;
        enum object_type type;
        void *otherbuf = read_sha1_file(entry->delta->sha1, &type, &othersize);
        void *delta_buf;

        if (!otherbuf)
                die("unable to read %s", sha1_to_hex(entry->delta->sha1));
        delta_buf = diff_delta(otherbuf, othersize,
                               buf, size, &delta_size, 0);
        if (!delta_buf || delta_size != entry->delta_size)
                die("delta size changed");
        free(buf);
        free(otherbuf);
        return delta_buf;
}

/*
 * The per-object header is a pretty dense thing, which is
 *  - first byte: low four bits are "size", then three bits of "type",
 *    and the high bit is "size continues".
 *  - each byte afterwards: low seven bits are size continuation,
 *    with the high bit being "size continues"
 */
static int encode_header(enum object_type type, unsigned long size, unsigned char *hdr)
{
        int n = 1;
        unsigned char c;

        if (type < OBJ_COMMIT || type > OBJ_REF_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;
}

/*
 * we are going to reuse the existing object data as is.  make
 * sure it is not corrupt.
 */
static int check_pack_inflate(struct packed_git *p,
                struct pack_window **w_curs,
                off_t offset,
                off_t len,
                unsigned long expect)
{
        z_stream stream;
        unsigned char fakebuf[4096], *in;
        int st;

        memset(&stream, 0, sizeof(stream));
        inflateInit(&stream);
        do {
                in = use_pack(p, w_curs, offset, &stream.avail_in);
                stream.next_in = in;
                stream.next_out = fakebuf;
                stream.avail_out = sizeof(fakebuf);
                st = inflate(&stream, Z_FINISH);
                offset += stream.next_in - in;
        } while (st == Z_OK || st == Z_BUF_ERROR);
        inflateEnd(&stream);
        return (st == Z_STREAM_END &&
                stream.total_out == expect &&
                stream.total_in == len) ? 0 : -1;
}

static void copy_pack_data(struct sha1file *f,
                struct packed_git *p,
                struct pack_window **w_curs,
                off_t offset,
                off_t len)
{
        unsigned char *in;
        unsigned int avail;

        while (len) {
                in = use_pack(p, w_curs, offset, &avail);
                if (avail > len)
                        avail = (unsigned int)len;
                sha1write(f, in, avail);
                offset += avail;
                len -= avail;
        }
}

static int check_loose_inflate(unsigned char *data, unsigned long len, unsigned long expect)
{
        z_stream stream;
        unsigned char fakebuf[4096];
        int st;

        memset(&stream, 0, sizeof(stream));
        stream.next_in = data;
        stream.avail_in = len;
        stream.next_out = fakebuf;
        stream.avail_out = sizeof(fakebuf);
        inflateInit(&stream);

        while (1) {
                st = inflate(&stream, Z_FINISH);
                if (st == Z_STREAM_END || st == Z_OK) {
                        st = (stream.total_out == expect &&
                              stream.total_in == len) ? 0 : -1;
                        break;
                }
                if (st != Z_BUF_ERROR) {
                        st = -1;
                        break;
                }
                stream.next_out = fakebuf;
                stream.avail_out = sizeof(fakebuf);
        }
        inflateEnd(&stream);
        return st;
}

static int revalidate_loose_object(struct object_entry *entry,
                                   unsigned char *map,
                                   unsigned long mapsize)
{
        /* we already know this is a loose object with new type header. */
        enum object_type type;
        unsigned long size, used;

        if (pack_to_stdout)
                return 0;

        used = unpack_object_header_gently(map, mapsize, &type, &size);
        if (!used)
                return -1;
        map += used;
        mapsize -= used;
        return check_loose_inflate(map, mapsize, size);
}

static off_t write_object(struct sha1file *f,
                                  struct object_entry *entry)
{
        unsigned long size;
        enum object_type type;
        void *buf;
        unsigned char header[10];
        unsigned hdrlen;
        off_t datalen;
        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_REF_DELTA || obj_type == OBJ_OFS_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 (!entry->in_pack && !entry->delta) {
                unsigned char *map;
                unsigned long mapsize;
                map = map_sha1_file(entry->sha1, &mapsize);
                if (map && !legacy_loose_object(map)) {
                        /* We can copy straight into the pack file */
                        if (revalidate_loose_object(entry, map, mapsize))
                                die("corrupt loose object %s",
                                    sha1_to_hex(entry->sha1));
                        sha1write(f, map, mapsize);
                        munmap(map, mapsize);
                        written++;
                        reused++;
                        return mapsize;
                }
                if (map)
                        munmap(map, mapsize);
        }

        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 = (allow_ofs_delta && entry->delta->offset) ?
                                OBJ_OFS_DELTA : OBJ_REF_DELTA;
                }
                /*
                 * The object header is a byte of 'type' followed by zero or
                 * more bytes of length.
                 */
                hdrlen = encode_header(obj_type, size, header);
                sha1write(f, header, hdrlen);

                if (obj_type == OBJ_OFS_DELTA) {
                        /*
                         * Deltas with relative base contain an additional
                         * encoding of the relative offset for the delta
                         * base from this object's position in the pack.
                         */
                        off_t ofs = entry->offset - entry->delta->offset;
                        unsigned pos = sizeof(header) - 1;
                        header[pos] = ofs & 127;
                        while (ofs >>= 7)
                                header[--pos] = 128 | (--ofs & 127);
                        sha1write(f, header + pos, sizeof(header) - pos);
                        hdrlen += sizeof(header) - pos;
                } else if (obj_type == OBJ_REF_DELTA) {
                        /*
                         * Deltas with a base reference contain
                         * an additional 20 bytes for the base sha1.
                         */
                        sha1write(f, entry->delta->sha1, 20);
                        hdrlen += 20;
                }
                datalen = sha1write_compressed(f, buf, size);
                free(buf);
        }
        else {
                struct packed_git *p = entry->in_pack;
                struct pack_window *w_curs = NULL;
                off_t offset;

                if (entry->delta) {
                        obj_type = (allow_ofs_delta && entry->delta->offset) ?
                                OBJ_OFS_DELTA : OBJ_REF_DELTA;
                        reused_delta++;
                }
                hdrlen = encode_header(obj_type, entry->size, header);
                sha1write(f, header, hdrlen);
                if (obj_type == OBJ_OFS_DELTA) {
                        off_t ofs = entry->offset - entry->delta->offset;
                        unsigned pos = sizeof(header) - 1;
                        header[pos] = ofs & 127;
                        while (ofs >>= 7)
                                header[--pos] = 128 | (--ofs & 127);
                        sha1write(f, header + pos, sizeof(header) - pos);
                        hdrlen += sizeof(header) - pos;
                } else if (obj_type == OBJ_REF_DELTA) {
                        sha1write(f, entry->delta->sha1, 20);
                        hdrlen += 20;
                }

                offset = entry->in_pack_offset + entry->in_pack_header_size;
                datalen = find_packed_object_size(p, entry->in_pack_offset)
                                - entry->in_pack_header_size;
                if (!pack_to_stdout && check_pack_inflate(p, &w_curs,
                                offset, datalen, entry->size))
                        die("corrupt delta in pack %s", sha1_to_hex(entry->sha1));
                copy_pack_data(f, p, &w_curs, offset, datalen);
                unuse_pack(&w_curs);
                reused++;
        }
        if (entry->delta)
                written_delta++;
        written++;
        return hdrlen + datalen;
}

static off_t write_one(struct sha1file *f,
                               struct object_entry *e,
                               off_t offset)
{
        if (e->offset || e->preferred_base)
                /* offset starts from header size and cannot be zero
                 * if it is written already.
                 */
                return offset;
        /* if we are deltified, write out its base object first. */
        if (e->delta)
                offset = write_one(f, e->delta, offset);
        e->offset = offset;
        return offset + write_object(f, e);
}

static void write_pack_file(void)
{
        uint32_t i;
        struct sha1file *f;
        off_t offset;
        struct pack_header hdr;
        unsigned last_percent = 999;
        int do_progress = progress;

        if (!base_name) {
                f = sha1fd(1, "<stdout>");
                do_progress >>= 1;
        }
        else
                f = sha1create("%s-%s.%s", base_name,
                               sha1_to_hex(object_list_sha1), "pack");
        if (do_progress)
                fprintf(stderr, "Writing %u objects.\n", nr_result);

        hdr.hdr_signature = htonl(PACK_SIGNATURE);
        hdr.hdr_version = htonl(PACK_VERSION);
        hdr.hdr_entries = htonl(nr_result);
        sha1write(f, &hdr, sizeof(hdr));
        offset = sizeof(hdr);
        if (!nr_result)
                goto done;
        for (i = 0; i < nr_objects; i++) {
                offset = write_one(f, objects + i, offset);
                if (do_progress) {
                        unsigned percent = written * 100 / nr_result;
                        if (progress_update || percent != last_percent) {
                                fprintf(stderr, "%4u%% (%u/%u) done\r",
                                        percent, written, nr_result);
                                progress_update = 0;
                                last_percent = percent;
                        }
                }
        }
        if (do_progress)
                fputc('\n', stderr);
 done:
        if (written != nr_result)
                die("wrote %u objects while expecting %u", written, nr_result);
        sha1close(f, pack_file_sha1, 1);
}

static void write_index_file(void)
{
        uint32_t i;
        struct sha1file *f = sha1create("%s-%s.%s", base_name,
                                        sha1_to_hex(object_list_sha1), "idx");
        struct object_entry **list = sorted_by_sha;
        struct object_entry **last = list + nr_result;
        uint32_t array[256];

        /*
         * Write the first-level table (the list is sorted,
         * but we use a 256-entry lookup to be able to avoid
         * having to do eight extra binary search iterations).
         */
        for (i = 0; i < 256; i++) {
                struct object_entry **next = list;
                while (next < last) {
                        struct object_entry *entry = *next;
                        if (entry->sha1[0] != i)
                                break;
                        next++;
                }
                array[i] = htonl(next - sorted_by_sha);
                list = next;
        }
        sha1write(f, array, 256 * 4);

        /*
         * Write the actual SHA1 entries..
         */
        list = sorted_by_sha;
        for (i = 0; i < nr_result; i++) {
                struct object_entry *entry = *list++;
                uint32_t offset = htonl(entry->offset);
                sha1write(f, &offset, 4);
                sha1write(f, entry->sha1, 20);
        }
        sha1write(f, pack_file_sha1, 20);
        sha1close(f, NULL, 1);
}

static int locate_object_entry_hash(const unsigned char *sha1)
{
        int i;
        unsigned int ui;
        memcpy(&ui, sha1, sizeof(unsigned int));
        i = ui % object_ix_hashsz;
        while (0 < object_ix[i]) {
                if (!hashcmp(sha1, objects[object_ix[i] - 1].sha1))
                        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)
{
        uint32_t i;
        struct object_entry *oe;

        object_ix_hashsz = nr_objects * 3;
        if (object_ix_hashsz < 1024)
                object_ix_hashsz = 1024;
        object_ix = xrealloc(object_ix, sizeof(int) * object_ix_hashsz);
        memset(object_ix, 0, sizeof(int) * object_ix_hashsz);
        for (i = 0, oe = objects; i < nr_objects; i++, oe++) {
                int ix = locate_object_entry_hash(oe->sha1);
                if (0 <= ix)
                        continue;
                ix = -1 - ix;
                object_ix[ix] = i + 1;
        }
}

static unsigned name_hash(const char *name)
{
        unsigned char c;
        unsigned hash = 0;

        /*
         * This effectively just creates a sortable number from the
         * last sixteen non-whitespace characters. Last characters
         * count "most", so things that end in ".c" sort together.
         */
        while ((c = *name++) != 0) {
                if (isspace(c))
                        continue;
                hash = (hash >> 2) + (c << 24);
        }
        return hash;
}

static int add_object_entry(const unsigned char *sha1, unsigned hash, int exclude)
{
        uint32_t idx = nr_objects;
        struct object_entry *entry;
        struct packed_git *p;
        off_t found_offset = 0;
        struct packed_git *found_pack = NULL;
        int ix, status = 0;

        if (!exclude) {
                for (p = packed_git; p; p = p->next) {
                        off_t offset = find_pack_entry_one(sha1, p);
                        if (offset) {
                                if (incremental)
                                        return 0;
                                if (local && !p->pack_local)
                                        return 0;
                                if (!found_pack) {
                                        found_offset = offset;
                                        found_pack = p;
                                }
                        }
                }
        }
        if ((entry = locate_object_entry(sha1)) != NULL)
                goto already_added;

        if (idx >= nr_alloc) {
                nr_alloc = (idx + 1024) * 3 / 2;
                objects = xrealloc(objects, nr_alloc * sizeof(*entry));
        }
        entry = objects + idx;
        nr_objects = idx + 1;
        memset(entry, 0, sizeof(*entry));
        hashcpy(entry->sha1, sha1);
        entry->hash = hash;

        if (object_ix_hashsz * 3 <= nr_objects * 4)
                rehash_objects();
        else {
                ix = locate_object_entry_hash(entry->sha1);
                if (0 <= ix)
                        die("internal error in object hashing.");
                object_ix[-1 - ix] = idx + 1;
        }
        status = 1;

 already_added:
        if (progress_update) {
                fprintf(stderr, "Counting objects...%u\r", nr_objects);
                progress_update = 0;
        }
        if (exclude)
                entry->preferred_base = 1;
        else {
                if (found_pack) {
                        entry->in_pack = found_pack;
                        entry->in_pack_offset = found_offset;
                }
        }
        return status;
}

struct pbase_tree_cache {
        unsigned char sha1[20];
        int ref;
        int temporary;
        void *tree_data;
        unsigned long tree_size;
};

static struct pbase_tree_cache *(pbase_tree_cache[256]);
static int pbase_tree_cache_ix(const unsigned char *sha1)
{
        return sha1[0] % ARRAY_SIZE(pbase_tree_cache);
}
static int pbase_tree_cache_ix_incr(int ix)
{
        return (ix+1) % ARRAY_SIZE(pbase_tree_cache);
}

static struct pbase_tree {
        struct pbase_tree *next;
        /* This is a phony "cache" entry; we are not
         * going to evict it nor find it through _get()
         * mechanism -- this is for the toplevel node that
         * would almost always change with any commit.
         */
        struct pbase_tree_cache pcache;
} *pbase_tree;

static struct pbase_tree_cache *pbase_tree_get(const unsigned char *sha1)
{
        struct pbase_tree_cache *ent, *nent;
        void *data;
        unsigned long size;
        enum object_type type;
        int neigh;
        int my_ix = pbase_tree_cache_ix(sha1);
        int available_ix = -1;

        /* pbase-tree-cache acts as a limited hashtable.
         * your object will be found at your index or within a few
         * slots after that slot if it is cached.
         */
        for (neigh = 0; neigh < 8; neigh++) {
                ent = pbase_tree_cache[my_ix];
                if (ent && !hashcmp(ent->sha1, sha1)) {
                        ent->ref++;
                        return ent;
                }
                else if (((available_ix < 0) && (!ent || !ent->ref)) ||
                         ((0 <= available_ix) &&
                          (!ent && pbase_tree_cache[available_ix])))
                        available_ix = my_ix;
                if (!ent)
                        break;
                my_ix = pbase_tree_cache_ix_incr(my_ix);
        }

        /* Did not find one.  Either we got a bogus request or
         * we need to read and perhaps cache.
         */
        data = read_sha1_file(sha1, &type, &size);
        if (!data)
                return NULL;
        if (type != OBJ_TREE) {
                free(data);
                return NULL;
        }

        /* We need to either cache or return a throwaway copy */

        if (available_ix < 0)
                ent = NULL;
        else {
                ent = pbase_tree_cache[available_ix];
                my_ix = available_ix;
        }

        if (!ent) {
                nent = xmalloc(sizeof(*nent));
                nent->temporary = (available_ix < 0);
        }
        else {
                /* evict and reuse */
                free(ent->tree_data);
                nent = ent;
        }
        hashcpy(nent->sha1, sha1);
        nent->tree_data = data;
        nent->tree_size = size;
        nent->ref = 1;
        if (!nent->temporary)
                pbase_tree_cache[my_ix] = nent;
        return nent;
}

static void pbase_tree_put(struct pbase_tree_cache *cache)
{
        if (!cache->temporary) {
                cache->ref--;
                return;
        }
        free(cache->tree_data);
        free(cache);
}

static int name_cmp_len(const char *name)
{
        int i;
        for (i = 0; name[i] && name[i] != '\n' && name[i] != '/'; i++)
                ;
        return i;
}

static void add_pbase_object(struct tree_desc *tree,
                             const char *name,
                             int cmplen,
                             const char *fullname)
{
        struct name_entry entry;

        while (tree_entry(tree,&entry)) {
                unsigned long size;
                enum object_type type;

                if (entry.pathlen != cmplen ||
                    memcmp(entry.path, name, cmplen) ||
                    !has_sha1_file(entry.sha1) ||
                    (type = sha1_object_info(entry.sha1, &size)) < 0)
                        continue;
                if (name[cmplen] != '/') {
                        unsigned hash = name_hash(fullname);
                        add_object_entry(entry.sha1, hash, 1);
                        return;
                }
                if (type == OBJ_TREE) {
                        struct tree_desc sub;
                        struct pbase_tree_cache *tree;
                        const char *down = name+cmplen+1;
                        int downlen = name_cmp_len(down);

                        tree = pbase_tree_get(entry.sha1);
                        if (!tree)
                                return;
                        sub.buf = tree->tree_data;
                        sub.size = tree->tree_size;

                        add_pbase_object(&sub, down, downlen, fullname);
                        pbase_tree_put(tree);
                }
        }
}

static unsigned *done_pbase_paths;
static int done_pbase_paths_num;
static int done_pbase_paths_alloc;
static int done_pbase_path_pos(unsigned hash)
{
        int lo = 0;
        int hi = done_pbase_paths_num;
        while (lo < hi) {
                int mi = (hi + lo) / 2;
                if (done_pbase_paths[mi] == hash)
                        return mi;
                if (done_pbase_paths[mi] < hash)
                        hi = mi;
                else
                        lo = mi + 1;
        }
        return -lo-1;
}

static int check_pbase_path(unsigned hash)
{
        int pos = (!done_pbase_paths) ? -1 : done_pbase_path_pos(hash);
        if (0 <= pos)
                return 1;
        pos = -pos - 1;
        if (done_pbase_paths_alloc <= done_pbase_paths_num) {
                done_pbase_paths_alloc = alloc_nr(done_pbase_paths_alloc);
                done_pbase_paths = xrealloc(done_pbase_paths,
                                            done_pbase_paths_alloc *
                                            sizeof(unsigned));
        }
        done_pbase_paths_num++;
        if (pos < done_pbase_paths_num)
                memmove(done_pbase_paths + pos + 1,
                        done_pbase_paths + pos,
                        (done_pbase_paths_num - pos - 1) * sizeof(unsigned));
        done_pbase_paths[pos] = hash;
        return 0;
}

static void add_preferred_base_object(const char *name, unsigned hash)
{
        struct pbase_tree *it;
        int cmplen = name_cmp_len(name);

        if (check_pbase_path(hash))
                return;

        for (it = pbase_tree; it; it = it->next) {
                if (cmplen == 0) {
                        hash = name_hash("");
                        add_object_entry(it->pcache.sha1, hash, 1);
                }
                else {
                        struct tree_desc tree;
                        tree.buf = it->pcache.tree_data;
                        tree.size = it->pcache.tree_size;
                        add_pbase_object(&tree, name, cmplen, name);
                }
        }
}

static void add_preferred_base(unsigned char *sha1)
{
        struct pbase_tree *it;
        void *data;
        unsigned long size;
        unsigned char tree_sha1[20];

        if (window <= num_preferred_base++)
                return;

        data = read_object_with_reference(sha1, tree_type, &size, tree_sha1);
        if (!data)
                return;

        for (it = pbase_tree; it; it = it->next) {
                if (!hashcmp(it->pcache.sha1, tree_sha1)) {
                        free(data);
                        return;
                }
        }

        it = xcalloc(1, sizeof(*it));
        it->next = pbase_tree;
        pbase_tree = it;

        hashcpy(it->pcache.sha1, tree_sha1);
        it->pcache.tree_data = data;
        it->pcache.tree_size = size;
}

static void check_object(struct object_entry *entry)
{
        if (entry->in_pack && !entry->preferred_base) {
                struct packed_git *p = entry->in_pack;
                struct pack_window *w_curs = NULL;
                unsigned long size, used;
                unsigned int avail;
                unsigned char *buf;
                struct object_entry *base_entry = NULL;

                buf = use_pack(p, &w_curs, entry->in_pack_offset, &avail);

                /* We want in_pack_type even if we do not reuse delta.
                 * There is no point not reusing non-delta representations.
                 */
                used = unpack_object_header_gently(buf, avail,
                                                   &entry->in_pack_type, &size);

                /* 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) {
                        unsigned char c;
                        const unsigned char *base_name;
                        off_t ofs;
                        unsigned long used_0;
                        /* there is at least 20 bytes left in the pack */
                        switch (entry->in_pack_type) {
                        case OBJ_REF_DELTA:
                                base_name = use_pack(p, &w_curs,
                                        entry->in_pack_offset + used, NULL);
                                used += 20;
                                break;
                        case OBJ_OFS_DELTA:
                                buf = use_pack(p, &w_curs,
                                        entry->in_pack_offset + used, NULL);
                                used_0 = 0;
                                c = buf[used_0++];
                                ofs = c & 127;
                                while (c & 128) {
                                        ofs += 1;
                                        if (!ofs || ofs & ~(~0UL >> 7))
                                                die("delta base offset overflow in pack for %s",
                                                    sha1_to_hex(entry->sha1));
                                        c = buf[used_0++];
                                        ofs = (ofs << 7) + (c & 127);
                                }
                                if (ofs >= entry->in_pack_offset)
                                        die("delta base offset out of bound for %s",
                                            sha1_to_hex(entry->sha1));
                                ofs = entry->in_pack_offset - ofs;
                                base_name = find_packed_object_name(p, ofs);
                                used += used_0;
                                break;
                        default:
                                base_name = NULL;
                        }
                        if (base_name)
                                base_entry = locate_object_entry(base_name);
                }
                unuse_pack(&w_curs);
                entry->in_pack_header_size = used;

                if (base_entry) {

                        /* 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 = size;
                        entry->delta = base_entry;
                        entry->type = entry->in_pack_type;

                        entry->delta_sibling = base_entry->delta_child;
                        base_entry->delta_child = entry;

                        return;
                }
                /* Otherwise we would do the usual */
        }

        entry->type = sha1_object_info(entry->sha1, &entry->size);
        if (entry->type < 0)
                die("unable to get type of object %s",
                    sha1_to_hex(entry->sha1));
}

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)
{
        uint32_t i;
        struct object_entry *entry;

        prepare_pack_ix();
        for (i = 0, entry = objects; i < nr_objects; i++, entry++)
                check_object(entry);

        if (nr_objects == nr_result) {
                /*
                 * Depth of objects that depend on the entry -- this
                 * is subtracted from depth-max to break too deep
                 * delta chain because of delta data reusing.
                 * However, we loosen this restriction when we know we
                 * are creating a thin pack -- it will have to be
                 * expanded on the other end anyway, so do not
                 * artificially cut the delta chain and let it go as
                 * deep as it wants.
                 */
                for (i = 0, entry = objects; i < nr_objects; i++, entry++)
                        if (!entry->delta && entry->delta_child)
                                entry->delta_limit =
                                        check_delta_limit(entry, 1);
        }
}

typedef int (*entry_sort_t)(const struct object_entry *, const struct object_entry *);

static entry_sort_t current_sort;

static int sort_comparator(const void *_a, const void *_b)
{
        struct object_entry *a = *(struct object_entry **)_a;
        struct object_entry *b = *(struct object_entry **)_b;
        return current_sort(a,b);
}

static struct object_entry **create_sorted_list(entry_sort_t sort)
{
        struct object_entry **list = xmalloc(nr_objects * sizeof(struct object_entry *));
        uint32_t i;

        for (i = 0; i < nr_objects; i++)
                list[i] = objects + i;
        current_sort = sort;
        qsort(list, nr_objects, sizeof(struct object_entry *), sort_comparator);
        return list;
}

static int sha1_sort(const struct object_entry *a, const struct object_entry *b)
{
        return hashcmp(a->sha1, b->sha1);
}

static struct object_entry **create_final_object_list(void)
{
        struct object_entry **list;
        uint32_t i, j;

        for (i = nr_result = 0; i < nr_objects; i++)
                if (!objects[i].preferred_base)
                        nr_result++;
        list = xmalloc(nr_result * sizeof(struct object_entry *));
        for (i = j = 0; i < nr_objects; i++) {
                if (!objects[i].preferred_base)
                        list[j++] = objects + i;
        }
        current_sort = sha1_sort;
        qsort(list, nr_result, sizeof(struct object_entry *), sort_comparator);
        return list;
}

static int type_size_sort(const struct object_entry *a, const struct object_entry *b)
{
        if (a->type < b->type)
                return -1;
        if (a->type > b->type)
                return 1;
        if (a->hash < b->hash)
                return -1;
        if (a->hash > b->hash)
                return 1;
        if (a->preferred_base < b->preferred_base)
                return -1;
        if (a->preferred_base > b->preferred_base)
                return 1;
        if (a->size < b->size)
                return -1;
        if (a->size > b->size)
                return 1;
        return a < b ? -1 : (a > b);
}

struct unpacked {
        struct object_entry *entry;
        void *data;
        struct delta_index *index;
};

/*
 * We search for deltas _backwards_ in a list sorted by type and
 * by size, so that we see progressively smaller and smaller files.
 * That's because we prefer deltas to be from the bigger file
 * to the smaller - deletes are potentially cheaper, but perhaps
 * more importantly, the bigger file is likely the more recent
 * one.
 */
static int try_delta(struct unpacked *trg, struct unpacked *src,
                     unsigned max_depth)
{
        struct object_entry *trg_entry = trg->entry;
        struct object_entry *src_entry = src->entry;
        unsigned long trg_size, src_size, delta_size, sizediff, max_size, sz;
        enum object_type type;
        void *delta_buf;

        /* Don't bother doing diffs between different types */
        if (trg_entry->type != src_entry->type)
                return -1;

        /* We do not compute delta to *create* objects we are not
         * going to pack.
         */
        if (trg_entry->preferred_base)
                return -1;

        /*
         * We do not bother to try a delta that we discarded
         * on an earlier try, but only when reusing delta data.
         */
        if (!no_reuse_delta && trg_entry->in_pack &&
            trg_entry->in_pack == src_entry->in_pack &&
            trg_entry->in_pack_type != OBJ_REF_DELTA &&
            trg_entry->in_pack_type != OBJ_OFS_DELTA)
                return 0;

        /*
         * If the current object is at pack edge, take the depth the
         * objects that depend on the current object into account --
         * otherwise they would become too deep.
         */
        if (trg_entry->delta_child) {
                if (max_depth <= trg_entry->delta_limit)
                        return 0;
                max_depth -= trg_entry->delta_limit;
        }
        if (src_entry->depth >= max_depth)
                return 0;

        /* Now some size filtering heuristics. */
        trg_size = trg_entry->size;
        max_size = trg_size/2 - 20;
        max_size = max_size * (max_depth - src_entry->depth) / max_depth;
        if (max_size == 0)
                return 0;
        if (trg_entry->delta && trg_entry->delta_size <= max_size)
                max_size = trg_entry->delta_size-1;
        src_size = src_entry->size;
        sizediff = src_size < trg_size ? trg_size - src_size : 0;
        if (sizediff >= max_size)
                return 0;

        /* Load data if not already done */
        if (!trg->data) {
                trg->data = read_sha1_file(trg_entry->sha1, &type, &sz);
                if (sz != trg_size)
                        die("object %s inconsistent object length (%lu vs %lu)",
                            sha1_to_hex(trg_entry->sha1), sz, trg_size);
        }
        if (!src->data) {
                src->data = read_sha1_file(src_entry->sha1, &type, &sz);
                if (sz != src_size)
                        die("object %s inconsistent object length (%lu vs %lu)",
                            sha1_to_hex(src_entry->sha1), sz, src_size);
        }
        if (!src->index) {
                src->index = create_delta_index(src->data, src_size);
                if (!src->index)
                        die("out of memory");
        }

        delta_buf = create_delta(src->index, trg->data, trg_size, &delta_size, max_size);
        if (!delta_buf)
                return 0;

        trg_entry->delta = src_entry;
        trg_entry->delta_size = delta_size;
        trg_entry->depth = src_entry->depth + 1;
        free(delta_buf);
        return 1;
}

static void progress_interval(int signum)
{
        progress_update = 1;
}

static void find_deltas(struct object_entry **list, int window, int depth)
{
        uint32_t i = nr_objects, idx = 0, processed = 0;
        unsigned int array_size = window * sizeof(struct unpacked);
        struct unpacked *array;
        unsigned last_percent = 999;

        if (!nr_objects)
                return;
        array = xmalloc(array_size);
        memset(array, 0, array_size);
        if (progress)
                fprintf(stderr, "Deltifying %u objects.\n", nr_result);

        do {
                struct object_entry *entry = list[--i];
                struct unpacked *n = array + idx;
                int j;

                if (!entry->preferred_base)
                        processed++;

                if (progress) {
                        unsigned percent = processed * 100 / nr_result;
                        if (percent != last_percent || progress_update) {
                                fprintf(stderr, "%4u%% (%u/%u) done\r",
                                        percent, processed, nr_result);
                                progress_update = 0;
                                last_percent = percent;
                        }
                }

                if (entry->delta)
                        /* This happens if we decided to reuse existing
                         * delta from a pack.  "!no_reuse_delta &&" is implied.
                         */
                        continue;

                if (entry->size < 50)
                        continue;
                free_delta_index(n->index);
                n->index = NULL;
                free(n->data);
                n->data = NULL;
                n->entry = entry;

                j = window;
                while (--j > 0) {
                        uint32_t other_idx = idx + j;
                        struct unpacked *m;
                        if (other_idx >= window)
                                other_idx -= window;
                        m = array + other_idx;
                        if (!m->entry)
                                break;
                        if (try_delta(n, m, depth) < 0)
                                break;
                }
                /* if we made n a delta, and if n is already at max
                 * depth, leaving it in the window is pointless.  we
                 * should evict it first.
                 */
                if (entry->delta && depth <= entry->depth)
                        continue;

                idx++;
                if (idx >= window)
                        idx = 0;
        } while (i > 0);

        if (progress)
                fputc('\n', stderr);

        for (i = 0; i < window; ++i) {
                free_delta_index(array[i].index);
                free(array[i].data);
        }
        free(array);
}

static void prepare_pack(int window, int depth)
{
        get_object_details();
        sorted_by_type = create_sorted_list(type_size_sort);
        if (window && depth)
                find_deltas(sorted_by_type, window+1, depth);
}

static int reuse_cached_pack(unsigned char *sha1)
{
        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 %u objects pack %s\n", nr_objects,
                        sha1_to_hex(sha1));

        if (pack_to_stdout) {
                if (copy_fd(ifd, 1))
                        exit(1);
                close(ifd);
        }
        else {
                char name[PATH_MAX];
                snprintf(name, sizeof(name),
                         "%s-%s.%s", base_name, sha1_to_hex(sha1), "pack");
                ofd = open(name, O_CREAT | O_EXCL | O_WRONLY, 0666);
                if (ofd < 0)
                        die("unable to open %s (%s)", name, strerror(errno));
                if (copy_fd(ifd, ofd))
                        exit(1);
                close(ifd);

                snprintf(name, sizeof(name),
                         "%s-%s.%s", base_name, sha1_to_hex(sha1), "idx");
                ofd = open(name, O_CREAT | O_EXCL | O_WRONLY, 0666);
                if (ofd < 0)
                        die("unable to open %s (%s)", name, strerror(errno));
                if (copy_fd(ifd_ix, ofd))
                        exit(1);
                close(ifd_ix);
                puts(sha1_to_hex(sha1));
        }

        return 1;
}

static void setup_progress_signal(void)
{
        struct sigaction sa;
        struct itimerval v;

        memset(&sa, 0, sizeof(sa));
        sa.sa_handler = progress_interval;
        sigemptyset(&sa.sa_mask);
        sa.sa_flags = SA_RESTART;
        sigaction(SIGALRM, &sa, NULL);

        v.it_interval.tv_sec = 1;
        v.it_interval.tv_usec = 0;
        v.it_value = v.it_interval;
        setitimer(ITIMER_REAL, &v, NULL);
}

static int git_pack_config(const char *k, const char *v)
{
        if(!strcmp(k, "pack.window")) {
                window = git_config_int(k, v);
                return 0;
        }
        return git_default_config(k, v);
}

static void read_object_list_from_stdin(void)
{
        char line[40 + 1 + PATH_MAX + 2];
        unsigned char sha1[20];
        unsigned hash;

        for (;;) {
                if (!fgets(line, sizeof(line), stdin)) {
                        if (feof(stdin))
                                break;
                        if (!ferror(stdin))
                                die("fgets returned NULL, not EOF, not error!");
                        if (errno != EINTR)
                                die("fgets: %s", strerror(errno));
                        clearerr(stdin);
                        continue;
                }
                if (line[0] == '-') {
                        if (get_sha1_hex(line+1, sha1))
                                die("expected edge sha1, got garbage:\n %s",
                                    line);
                        add_preferred_base(sha1);
                        continue;
                }
                if (get_sha1_hex(line, sha1))
                        die("expected sha1, got garbage:\n %s", line);

                hash = name_hash(line+41);
                add_preferred_base_object(line+41, hash);
                add_object_entry(sha1, hash, 0);
        }
}

static void show_commit(struct commit *commit)
{
        unsigned hash = name_hash("");
        add_preferred_base_object("", hash);
        add_object_entry(commit->object.sha1, hash, 0);
}

static void show_object(struct object_array_entry *p)
{
        unsigned hash = name_hash(p->name);
        add_preferred_base_object(p->name, hash);
        add_object_entry(p->item->sha1, hash, 0);
}

static void show_edge(struct commit *commit)
{
        add_preferred_base(commit->object.sha1);
}

static void get_object_list(int ac, const char **av)
{
        struct rev_info revs;
        char line[1000];
        int flags = 0;

        init_revisions(&revs, NULL);
        save_commit_buffer = 0;
        track_object_refs = 0;
        setup_revisions(ac, av, &revs, NULL);

        while (fgets(line, sizeof(line), stdin) != NULL) {
                int len = strlen(line);
                if (line[len - 1] == '\n')
                        line[--len] = 0;
                if (!len)
                        break;
                if (*line == '-') {
                        if (!strcmp(line, "--not")) {
                                flags ^= UNINTERESTING;
                                continue;
                        }
                        die("not a rev '%s'", line);
                }
                if (handle_revision_arg(line, &revs, flags, 1))
                        die("bad revision '%s'", line);
        }

        prepare_revision_walk(&revs);
        mark_edges_uninteresting(revs.commits, &revs, show_edge);
        traverse_commit_list(&revs, show_commit, show_object);
}

int cmd_pack_objects(int argc, const char **argv, const char *prefix)
{
        SHA_CTX ctx;
        int depth = 10;
        struct object_entry **list;
        int use_internal_rev_list = 0;
        int thin = 0;
        uint32_t i;
        const char **rp_av;
        int rp_ac_alloc = 64;
        int rp_ac;

        rp_av = xcalloc(rp_ac_alloc, sizeof(*rp_av));

        rp_av[0] = "pack-objects";
        rp_av[1] = "--objects"; /* --thin will make it --objects-edge */
        rp_ac = 2;

        git_config(git_pack_config);

        progress = isatty(2);
        for (i = 1; i < argc; i++) {
                const char *arg = argv[i];

                if (*arg != '-')
                        break;

                if (!strcmp("--non-empty", arg)) {
                        non_empty = 1;
                        continue;
                }
                if (!strcmp("--local", arg)) {
                        local = 1;
                        continue;
                }
                if (!strcmp("--incremental", arg)) {
                        incremental = 1;
                        continue;
                }
                if (!prefixcmp(arg, "--window=")) {
                        char *end;
                        window = strtoul(arg+9, &end, 0);
                        if (!arg[9] || *end)
                                usage(pack_usage);
                        continue;
                }
                if (!prefixcmp(arg, "--depth=")) {
                        char *end;
                        depth = strtoul(arg+8, &end, 0);
                        if (!arg[8] || *end)
                                usage(pack_usage);
                        continue;
                }
                if (!strcmp("--progress", arg)) {
                        progress = 1;
                        continue;
                }
                if (!strcmp("--all-progress", arg)) {
                        progress = 2;
                        continue;
                }
                if (!strcmp("-q", arg)) {
                        progress = 0;
                        continue;
                }
                if (!strcmp("--no-reuse-delta", arg)) {
                        no_reuse_delta = 1;
                        continue;
                }
                if (!strcmp("--delta-base-offset", arg)) {
                        allow_ofs_delta = 1;
                        continue;
                }
                if (!strcmp("--stdout", arg)) {
                        pack_to_stdout = 1;
                        continue;
                }
                if (!strcmp("--revs", arg)) {
                        use_internal_rev_list = 1;
                        continue;
                }
                if (!strcmp("--unpacked", arg) ||
                    !prefixcmp(arg, "--unpacked=") ||
                    !strcmp("--reflog", arg) ||
                    !strcmp("--all", arg)) {
                        use_internal_rev_list = 1;
                        if (rp_ac >= rp_ac_alloc - 1) {
                                rp_ac_alloc = alloc_nr(rp_ac_alloc);
                                rp_av = xrealloc(rp_av,
                                                 rp_ac_alloc * sizeof(*rp_av));
                        }
                        rp_av[rp_ac++] = arg;
                        continue;
                }
                if (!strcmp("--thin", arg)) {
                        use_internal_rev_list = 1;
                        thin = 1;
                        rp_av[1] = "--objects-edge";
                        continue;
                }
                usage(pack_usage);
        }

        /* Traditionally "pack-objects [options] base extra" failed;
         * we would however want to take refs parameter that would
         * have been given to upstream rev-list ourselves, which means
         * we somehow want to say what the base name is.  So the
         * syntax would be:
         *
         * pack-objects [options] base <refs...>
         *
         * in other words, we would treat the first non-option as the
         * base_name and send everything else to the internal revision
         * walker.
         */

        if (!pack_to_stdout)
                base_name = argv[i++];

        if (pack_to_stdout != !base_name)
                usage(pack_usage);

        if (!pack_to_stdout && thin)
                die("--thin cannot be used to build an indexable pack.");

        prepare_packed_git();

        if (progress) {
                fprintf(stderr, "Generating pack...\n");
                setup_progress_signal();
        }

        if (!use_internal_rev_list)
                read_object_list_from_stdin();
        else {
                rp_av[rp_ac] = NULL;
                get_object_list(rp_ac, rp_av);
        }

        if (progress)
                fprintf(stderr, "Done counting %u objects.\n", nr_objects);
        sorted_by_sha = create_final_object_list();
        if (non_empty && !nr_result)
                return 0;

        SHA1_Init(&ctx);
        list = sorted_by_sha;
        for (i = 0; i < nr_result; i++) {
                struct object_entry *entry = *list++;
                SHA1_Update(&ctx, entry->sha1, 20);
        }
        SHA1_Final(object_list_sha1, &ctx);
        if (progress && (nr_objects != nr_result))
                fprintf(stderr, "Result has %u objects.\n", nr_result);

        if (reuse_cached_pack(object_list_sha1))
                ;
        else {
                if (nr_result)
                        prepare_pack(window, depth);
                if (progress == 1 && 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 %u (delta %u), reused %u (delta %u)\n",
                        written, written_delta, reused, reused_delta);
        return 0;
}