git-pack-objects: cache small deltas between big objects

[git/gitweb-caching.git] / builtin-pack-objects.c

#include "builtin.h"
#include "cache.h"
#include "attr.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"
#include "progress.h"

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

struct object_entry {
        unsigned char sha1[20];
        uint32_t crc32;         /* crc of raw pack data for this object */
        off_t offset;           /* offset into the final pack file */
        unsigned long size;     /* uncompressed size */
        unsigned int hash;      /* name hint hash */
        unsigned int depth;     /* delta depth */
        struct packed_git *in_pack;     /* already in pack */
        off_t in_pack_offset;
        struct object_entry *delta;     /* delta base object */
        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
                                             */
        void *delta_data;       /* cached delta (uncompressed) */
        unsigned long delta_size;       /* delta data size (uncompressed) */
        enum object_type type;
        enum object_type in_pack_type;  /* could be delta */
        unsigned char in_pack_header_size;
        unsigned char preferred_base; /* we do not pack this, but is available
                                       * to be used as the base object to delta
                                       * objects against.
                                       */
        unsigned char no_try_delta;
};

/*
 * 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.
 */
static struct object_entry *objects;
static struct object_entry **written_list;
static uint32_t nr_objects, nr_alloc, nr_result, nr_written;

static int non_empty;
static int no_reuse_delta, no_reuse_object;
static int local;
static int incremental;
static int allow_ofs_delta;
static const char *pack_tmp_name, *idx_tmp_name;
static char tmpname[PATH_MAX];
static const char *base_name;
static unsigned char pack_file_sha1[20];
static int progress = 1;
static int window = 10;
static uint32_t pack_size_limit;
static int depth = 50;
static int pack_to_stdout;
static int num_preferred_base;
static struct progress progress_state;
static int pack_compression_level = Z_DEFAULT_COMPRESSION;
static int pack_compression_seen;

static unsigned long delta_cache_size = 0;
static unsigned long max_delta_cache_size = 0;

/*
 * The object names in objects array are hashed with this hashtable,
 * to help looking up the entry by object name.
 * 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 = p->num_objects;
        int i;
        const char *index = p->index_data;

        rix->revindex = xmalloc(sizeof(*rix->revindex) * (num_ent + 1));
        index += 4 * 256;

        if (p->index_version > 1) {
                const uint32_t *off_32 =
                        (uint32_t *)(index + 8 + p->num_objects * (20 + 4));
                const uint32_t *off_64 = off_32 + p->num_objects;
                for (i = 0; i < num_ent; i++) {
                        uint32_t off = ntohl(*off_32++);
                        if (!(off & 0x80000000)) {
                                rix->revindex[i].offset = off;
                        } else {
                                rix->revindex[i].offset =
                                        ((uint64_t)ntohl(*off_64++)) << 32;
                                rix->revindex[i].offset |=
                                        ntohl(*off_64++);
                        }
                        rix->revindex[i].nr = i;
                }
        } else {
                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 = p->num_objects + 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 const unsigned char *find_packed_object_name(struct packed_git *p,
                                                    off_t ofs)
{
        struct revindex_entry *entry = find_packed_object(p, ofs);
        return nth_packed_object_sha1(p, entry->nr);
}

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 int check_pack_crc(struct packed_git *p, struct pack_window **w_curs,
                          off_t offset, off_t len, unsigned int nr)
{
        const uint32_t *index_crc;
        uint32_t data_crc = crc32(0, Z_NULL, 0);

        do {
                unsigned int avail;
                void *data = use_pack(p, w_curs, offset, &avail);
                if (avail > len)
                        avail = len;
                data_crc = crc32(data_crc, data, avail);
                offset += avail;
                len -= avail;
        } while (len);

        index_crc = p->index_data;
        index_crc += 2 + 256 + p->num_objects * (20/4) + nr;

        return data_crc != ntohl(*index_crc);
}

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 unsigned long write_object(struct sha1file *f,
                                  struct object_entry *entry,
                                  off_t write_offset)
{
        unsigned long size;
        enum object_type type;
        void *buf;
        unsigned char header[10];
        unsigned char dheader[10];
        unsigned hdrlen;
        off_t datalen;
        enum object_type obj_type;
        int to_reuse = 0;
        /* write limit if limited packsize and not first object */
        unsigned long limit = pack_size_limit && nr_written ?
                                pack_size_limit - write_offset : 0;
                                /* no if no delta */
        int usable_delta =      !entry->delta ? 0 :
                                /* yes if unlimited packfile */
                                !pack_size_limit ? 1 :
                                /* no if base written to previous pack */
                                entry->delta->offset == (off_t)-1 ? 0 :
                                /* otherwise double-check written to this
                                 * pack,  like we do below
                                 */
                                entry->delta->offset ? 1 : 0;

        if (!pack_to_stdout)
                crc32_begin(f);

        obj_type = entry->type;
        if (no_reuse_object)
                to_reuse = 0;   /* explicit */
        else 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)
                                /* check_object() decided it for us ... */
                to_reuse = usable_delta;
                                /* ... but pack split may override that */
        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) {
                z_stream stream;
                unsigned long maxsize;
                void *out;
                if (entry->delta_data && usable_delta) {
                        buf = entry->delta_data;
                        size = entry->delta_size;
                        obj_type = (allow_ofs_delta && entry->delta->offset) ?
                                OBJ_OFS_DELTA : OBJ_REF_DELTA;
                } else {
                        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 (usable_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;
                        } else {
                                /*
                                 * recover real object type in case
                                 * check_object() wanted to re-use a delta,
                                 * but we couldn't since base was in previous split pack
                                 */
                                obj_type = type;
                        }
                }
                /* compress the data to store and put compressed length in datalen */
                memset(&stream, 0, sizeof(stream));
                deflateInit(&stream, pack_compression_level);
                maxsize = deflateBound(&stream, size);
                out = xmalloc(maxsize);
                /* Compress it */
                stream.next_in = buf;
                stream.avail_in = size;
                stream.next_out = out;
                stream.avail_out = maxsize;
                while (deflate(&stream, Z_FINISH) == Z_OK)
                        /* nothing */;
                deflateEnd(&stream);
                datalen = stream.total_out;
                deflateEnd(&stream);
                /*
                 * The object header is a byte of 'type' followed by zero or
                 * more bytes of length.
                 */
                hdrlen = encode_header(obj_type, size, header);

                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(dheader) - 1;
                        dheader[pos] = ofs & 127;
                        while (ofs >>= 7)
                                dheader[--pos] = 128 | (--ofs & 127);
                        if (limit && hdrlen + sizeof(dheader) - pos + datalen + 20 >= limit) {
                                free(out);
                                free(buf);
                                return 0;
                        }
                        sha1write(f, header, hdrlen);
                        sha1write(f, dheader + pos, sizeof(dheader) - pos);
                        hdrlen += sizeof(dheader) - pos;
                } else if (obj_type == OBJ_REF_DELTA) {
                        /*
                         * Deltas with a base reference contain
                         * an additional 20 bytes for the base sha1.
                         */
                        if (limit && hdrlen + 20 + datalen + 20 >= limit) {
                                free(out);
                                free(buf);
                                return 0;
                        }
                        sha1write(f, header, hdrlen);
                        sha1write(f, entry->delta->sha1, 20);
                        hdrlen += 20;
                } else {
                        if (limit && hdrlen + datalen + 20 >= limit) {
                                free(out);
                                free(buf);
                                return 0;
                        }
                        sha1write(f, header, hdrlen);
                }
                sha1write(f, out, datalen);
                free(out);
                free(buf);
        }
        else {
                struct packed_git *p = entry->in_pack;
                struct pack_window *w_curs = NULL;
                struct revindex_entry *revidx;
                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);
                offset = entry->in_pack_offset;
                revidx = find_packed_object(p, offset);
                datalen = revidx[1].offset - offset;
                if (!pack_to_stdout && p->index_version > 1 &&
                    check_pack_crc(p, &w_curs, offset, datalen, revidx->nr))
                        die("bad packed object CRC for %s", sha1_to_hex(entry->sha1));
                offset += entry->in_pack_header_size;
                datalen -= entry->in_pack_header_size;
                if (obj_type == OBJ_OFS_DELTA) {
                        off_t ofs = entry->offset - entry->delta->offset;
                        unsigned pos = sizeof(dheader) - 1;
                        dheader[pos] = ofs & 127;
                        while (ofs >>= 7)
                                dheader[--pos] = 128 | (--ofs & 127);
                        if (limit && hdrlen + sizeof(dheader) - pos + datalen + 20 >= limit)
                                return 0;
                        sha1write(f, header, hdrlen);
                        sha1write(f, dheader + pos, sizeof(dheader) - pos);
                        hdrlen += sizeof(dheader) - pos;
                } else if (obj_type == OBJ_REF_DELTA) {
                        if (limit && hdrlen + 20 + datalen + 20 >= limit)
                                return 0;
                        sha1write(f, header, hdrlen);
                        sha1write(f, entry->delta->sha1, 20);
                        hdrlen += 20;
                } else {
                        if (limit && hdrlen + datalen + 20 >= limit)
                                return 0;
                        sha1write(f, header, hdrlen);
                }

                if (!pack_to_stdout && p->index_version == 1 &&
                    check_pack_inflate(p, &w_curs, offset, datalen, entry->size))
                        die("corrupt packed object for %s", sha1_to_hex(entry->sha1));
                copy_pack_data(f, p, &w_curs, offset, datalen);
                unuse_pack(&w_curs);
                reused++;
        }
        if (usable_delta)
                written_delta++;
        written++;
        if (!pack_to_stdout)
                entry->crc32 = crc32_end(f);
        return hdrlen + datalen;
}

static off_t write_one(struct sha1file *f,
                               struct object_entry *e,
                               off_t offset)
{
        unsigned long size;

        /* offset is non zero if object is written already. */
        if (e->offset || e->preferred_base)
                return offset;

        /* if we are deltified, write out base object first. */
        if (e->delta) {
                offset = write_one(f, e->delta, offset);
                if (!offset)
                        return 0;
        }

        e->offset = offset;
        size = write_object(f, e, offset);
        if (!size) {
                e->offset = 0;
                return 0;
        }
        written_list[nr_written++] = e;

        /* make sure off_t is sufficiently large not to wrap */
        if (offset > offset + size)
                die("pack too large for current definition of off_t");
        return offset + size;
}

static int open_object_dir_tmp(const char *path)
{
    snprintf(tmpname, sizeof(tmpname), "%s/%s", get_object_directory(), path);
    return mkstemp(tmpname);
}

/* forward declarations for write_pack_file */
static void write_index_file(off_t last_obj_offset, unsigned char *sha1);
static int adjust_perm(const char *path, mode_t mode);

static void write_pack_file(void)
{
        uint32_t i = 0, j;
        struct sha1file *f;
        off_t offset, offset_one, last_obj_offset = 0;
        struct pack_header hdr;
        int do_progress = progress >> pack_to_stdout;
        uint32_t nr_remaining = nr_result;

        if (do_progress)
                start_progress(&progress_state, "Writing %u objects...", "", nr_result);
        written_list = xmalloc(nr_objects * sizeof(struct object_entry *));

        do {
                if (pack_to_stdout) {
                        f = sha1fd(1, "<stdout>");
                } else {
                        int fd = open_object_dir_tmp("tmp_pack_XXXXXX");
                        if (fd < 0)
                                die("unable to create %s: %s\n", tmpname, strerror(errno));
                        pack_tmp_name = xstrdup(tmpname);
                        f = sha1fd(fd, pack_tmp_name);
                }

                hdr.hdr_signature = htonl(PACK_SIGNATURE);
                hdr.hdr_version = htonl(PACK_VERSION);
                hdr.hdr_entries = htonl(nr_remaining);
                sha1write(f, &hdr, sizeof(hdr));
                offset = sizeof(hdr);
                nr_written = 0;
                for (; i < nr_objects; i++) {
                        last_obj_offset = offset;
                        offset_one = write_one(f, objects + i, offset);
                        if (!offset_one)
                                break;
                        offset = offset_one;
                        if (do_progress)
                                display_progress(&progress_state, written);
                }

                /*
                 * Did we write the wrong # entries in the header?
                 * If so, rewrite it like in fast-import
                 */
                if (pack_to_stdout || nr_written == nr_remaining) {
                        sha1close(f, pack_file_sha1, 1);
                } else {
                        sha1close(f, pack_file_sha1, 0);
                        fixup_pack_header_footer(f->fd, pack_file_sha1, pack_tmp_name, nr_written);
                        close(f->fd);
                }

                if (!pack_to_stdout) {
                        unsigned char object_list_sha1[20];
                        mode_t mode = umask(0);

                        umask(mode);
                        mode = 0444 & ~mode;

                        write_index_file(last_obj_offset, object_list_sha1);
                        snprintf(tmpname, sizeof(tmpname), "%s-%s.pack",
                                 base_name, sha1_to_hex(object_list_sha1));
                        if (adjust_perm(pack_tmp_name, mode))
                                die("unable to make temporary pack file readable: %s",
                                    strerror(errno));
                        if (rename(pack_tmp_name, tmpname))
                                die("unable to rename temporary pack file: %s",
                                    strerror(errno));
                        snprintf(tmpname, sizeof(tmpname), "%s-%s.idx",
                                 base_name, sha1_to_hex(object_list_sha1));
                        if (adjust_perm(idx_tmp_name, mode))
                                die("unable to make temporary index file readable: %s",
                                    strerror(errno));
                        if (rename(idx_tmp_name, tmpname))
                                die("unable to rename temporary index file: %s",
                                    strerror(errno));
                        puts(sha1_to_hex(object_list_sha1));
                }

                /* mark written objects as written to previous pack */
                for (j = 0; j < nr_written; j++) {
                        written_list[j]->offset = (off_t)-1;
                }
                nr_remaining -= nr_written;
        } while (nr_remaining && i < nr_objects);

        free(written_list);
        if (do_progress)
                stop_progress(&progress_state);
        if (written != nr_result)
                die("wrote %u objects while expecting %u", written, nr_result);
        /*
         * We have scanned through [0 ... i).  Since we have written
         * the correct number of objects,  the remaining [i ... nr_objects)
         * items must be either already written (due to out-of-order delta base)
         * or a preferred base.  Count those which are neither and complain if any.
         */
        for (j = 0; i < nr_objects; i++) {
                struct object_entry *e = objects + i;
                j += !e->offset && !e->preferred_base;
        }
        if (j)
                die("wrote %u objects as expected but %u unwritten", written, j);
}

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

static uint32_t index_default_version = 1;
static uint32_t index_off32_limit = 0x7fffffff;

static void write_index_file(off_t last_obj_offset, unsigned char *sha1)
{
        struct sha1file *f;
        struct object_entry **sorted_by_sha, **list, **last;
        uint32_t array[256];
        uint32_t i, index_version;
        SHA_CTX ctx;

        int fd = open_object_dir_tmp("tmp_idx_XXXXXX");
        if (fd < 0)
                die("unable to create %s: %s\n", tmpname, strerror(errno));
        idx_tmp_name = xstrdup(tmpname);
        f = sha1fd(fd, idx_tmp_name);

        if (nr_written) {
                sorted_by_sha = written_list;
                qsort(sorted_by_sha, nr_written, sizeof(*sorted_by_sha), sha1_sort);
                list = sorted_by_sha;
                last = sorted_by_sha + nr_written;
        } else
                sorted_by_sha = list = last = NULL;

        /* if last object's offset is >= 2^31 we should use index V2 */
        index_version = (last_obj_offset >> 31) ? 2 : index_default_version;

        /* index versions 2 and above need a header */
        if (index_version >= 2) {
                struct pack_idx_header hdr;
                hdr.idx_signature = htonl(PACK_IDX_SIGNATURE);
                hdr.idx_version = htonl(index_version);
                sha1write(f, &hdr, sizeof(hdr));
        }

        /*
         * 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);

        /* Compute the SHA1 hash of sorted object names. */
        SHA1_Init(&ctx);

        /* Write the actual SHA1 entries. */
        list = sorted_by_sha;
        for (i = 0; i < nr_written; i++) {
                struct object_entry *entry = *list++;
                if (index_version < 2) {
                        uint32_t offset = htonl(entry->offset);
                        sha1write(f, &offset, 4);
                }
                sha1write(f, entry->sha1, 20);
                SHA1_Update(&ctx, entry->sha1, 20);
        }

        if (index_version >= 2) {
                unsigned int nr_large_offset = 0;

                /* write the crc32 table */
                list = sorted_by_sha;
                for (i = 0; i < nr_written; i++) {
                        struct object_entry *entry = *list++;
                        uint32_t crc32_val = htonl(entry->crc32);
                        sha1write(f, &crc32_val, 4);
                }

                /* write the 32-bit offset table */
                list = sorted_by_sha;
                for (i = 0; i < nr_written; i++) {
                        struct object_entry *entry = *list++;
                        uint32_t offset = (entry->offset <= index_off32_limit) ?
                                entry->offset : (0x80000000 | nr_large_offset++);
                        offset = htonl(offset);
                        sha1write(f, &offset, 4);
                }

                /* write the large offset table */
                list = sorted_by_sha;
                while (nr_large_offset) {
                        struct object_entry *entry = *list++;
                        uint64_t offset = entry->offset;
                        if (offset > index_off32_limit) {
                                uint32_t split[2];
                                split[0]        = htonl(offset >> 32);
                                split[1] = htonl(offset & 0xffffffff);
                                sha1write(f, split, 8);
                                nr_large_offset--;
                        }
                }
        }

        sha1write(f, pack_file_sha1, 20);
        sha1close(f, NULL, 1);
        SHA1_Final(sha1, &ctx);
}

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;

        if (!name)
                return 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 void setup_delta_attr_check(struct git_attr_check *check)
{
        static struct git_attr *attr_delta;

        if (!attr_delta)
                attr_delta = git_attr("delta", 5);

        check[0].attr = attr_delta;
}

static int no_try_delta(const char *path)
{
        struct git_attr_check check[1];

        setup_delta_attr_check(check);
        if (git_checkattr(path, ARRAY_SIZE(check), check))
                return 0;
        if (ATTR_FALSE(check->value))
                return 1;
        return 0;
}

static int add_object_entry(const unsigned char *sha1, enum object_type type,
                            const char *name, int exclude)
{
        struct object_entry *entry;
        struct packed_git *p, *found_pack = NULL;
        off_t found_offset = 0;
        int ix;
        unsigned hash = name_hash(name);

        ix = nr_objects ? locate_object_entry_hash(sha1) : -1;
        if (ix >= 0) {
                if (exclude) {
                        entry = objects + object_ix[ix] - 1;
                        if (!entry->preferred_base)
                                nr_result--;
                        entry->preferred_base = 1;
                }
                return 0;
        }

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

        if (nr_objects >= nr_alloc) {
                nr_alloc = (nr_alloc  + 1024) * 3 / 2;
                objects = xrealloc(objects, nr_alloc * sizeof(*entry));
        }

        entry = objects + nr_objects++;
        memset(entry, 0, sizeof(*entry));
        hashcpy(entry->sha1, sha1);
        entry->hash = hash;
        if (type)
                entry->type = type;
        if (exclude)
                entry->preferred_base = 1;
        else
                nr_result++;
        if (found_pack) {
                entry->in_pack = found_pack;
                entry->in_pack_offset = found_offset;
        }

        if (object_ix_hashsz * 3 <= nr_objects * 4)
                rehash_objects();
        else
                object_ix[-1 - ix] = nr_objects;

        if (progress)
                display_progress(&progress_state, nr_objects);

        if (name && no_try_delta(name))
                entry->no_try_delta = 1;

        return 1;
}

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;
        int cmp;

        while (tree_entry(tree,&entry)) {
                cmp = tree_entry_len(entry.path, entry.sha1) != cmplen ? 1 :
                      memcmp(name, entry.path, cmplen);
                if (cmp > 0)
                        continue;
                if (cmp < 0)
                        return;
                if (name[cmplen] != '/') {
                        add_object_entry(entry.sha1,
                                         S_ISDIR(entry.mode) ? OBJ_TREE : OBJ_BLOB,
                                         fullname, 1);
                        return;
                }
                if (S_ISDIR(entry.mode)) {
                        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;
                        init_tree_desc(&sub, tree->tree_data, 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)
{
        struct pbase_tree *it;
        int cmplen;
        unsigned hash = name_hash(name);

        if (!num_preferred_base || check_pbase_path(hash))
                return;

        cmplen = name_cmp_len(name);
        for (it = pbase_tree; it; it = it->next) {
                if (cmplen == 0) {
                        add_object_entry(it->pcache.sha1, OBJ_TREE, NULL, 1);
                }
                else {
                        struct tree_desc tree;
                        init_tree_desc(&tree, it->pcache.tree_data, 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) {
                struct packed_git *p = entry->in_pack;
                struct pack_window *w_curs = NULL;
                const unsigned char *base_ref = NULL;
                struct object_entry *base_entry;
                unsigned long used, used_0;
                unsigned int avail;
                off_t ofs;
                unsigned char *buf, c;

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

                /*
                 * We want in_pack_type even if we do not reuse delta
                 * since non-delta representations could still be reused.
                 */
                used = unpack_object_header_gently(buf, avail,
                                                   &entry->in_pack_type,
                                                   &entry->size);

                /*
                 * Determine if this is a delta and if so whether we can
                 * reuse it or not.  Otherwise let's find out as cheaply as
                 * possible what the actual type and size for this object is.
                 */
                switch (entry->in_pack_type) {
                default:
                        /* Not a delta hence we've already got all we need. */
                        entry->type = entry->in_pack_type;
                        entry->in_pack_header_size = used;
                        unuse_pack(&w_curs);
                        return;
                case OBJ_REF_DELTA:
                        if (!no_reuse_delta && !entry->preferred_base)
                                base_ref = use_pack(p, &w_curs,
                                                entry->in_pack_offset + used, NULL);
                        entry->in_pack_header_size = 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 || MSB(ofs, 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;
                        if (!no_reuse_delta && !entry->preferred_base)
                                base_ref = find_packed_object_name(p, ofs);
                        entry->in_pack_header_size = used + used_0;
                        break;
                }

                if (base_ref && (base_entry = locate_object_entry(base_ref))) {
                        /*
                         * If base_ref was set above that means we wish to
                         * reuse delta data, and we even found that base
                         * in the list of objects we want to pack. Goodie!
                         *
                         * 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.
                         */
                        entry->type = entry->in_pack_type;
                        entry->delta = base_entry;
                        entry->delta_sibling = base_entry->delta_child;
                        base_entry->delta_child = entry;
                        unuse_pack(&w_curs);
                        return;
                }

                if (entry->type) {
                        /*
                         * This must be a delta and we already know what the
                         * final object type is.  Let's extract the actual
                         * object size from the delta header.
                         */
                        entry->size = get_size_from_delta(p, &w_curs,
                                        entry->in_pack_offset + entry->in_pack_header_size);
                        unuse_pack(&w_curs);
                        return;
                }

                /*
                 * No choice but to fall back to the recursive delta walk
                 * with sha1_object_info() to find about the object type
                 * at this point...
                 */
                unuse_pack(&w_curs);
        }

        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 int pack_offset_sort(const void *_a, const void *_b)
{
        const struct object_entry *a = *(struct object_entry **)_a;
        const struct object_entry *b = *(struct object_entry **)_b;

        /* avoid filesystem trashing with loose objects */
        if (!a->in_pack && !b->in_pack)
                return hashcmp(a->sha1, b->sha1);

        if (a->in_pack < b->in_pack)
                return -1;
        if (a->in_pack > b->in_pack)
                return 1;
        return a->in_pack_offset < b->in_pack_offset ? -1 :
                        (a->in_pack_offset > b->in_pack_offset);
}

static void get_object_details(void)
{
        uint32_t i;
        struct object_entry **sorted_by_offset;

        sorted_by_offset = xcalloc(nr_objects, sizeof(struct object_entry *));
        for (i = 0; i < nr_objects; i++)
                sorted_by_offset[i] = objects + i;
        qsort(sorted_by_offset, nr_objects, sizeof(*sorted_by_offset), pack_offset_sort);

        prepare_pack_ix();
        for (i = 0; i < nr_objects; i++)
                check_object(sorted_by_offset[i]);
        free(sorted_by_offset);
}

static int type_size_sort(const void *_a, const void *_b)
{
        const struct object_entry *a = *(struct object_entry **)_a;
        const struct object_entry *b = *(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);  /* newest last */
}

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

static int delta_cacheable(struct unpacked *trg, struct unpacked *src,
                            unsigned long src_size, unsigned long trg_size,
                            unsigned long delta_size)
{
        if (max_delta_cache_size && delta_cache_size + delta_size > max_delta_cache_size)
                return 0;

        /* cache delta, if objects are large enough compared to delta size */
        if ((src_size >> 20) + (trg_size >> 21) > (delta_size >> 10))
                return 1;

        return 0;
}

/*
 * 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;

        /* Let's not bust the allowed depth. */
        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) {
                        static int warned = 0;
                        if (!warned++)
                                warning("suboptimal pack - out of memory");
                        return 0;
                }
        }

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

        if (trg_entry->delta_data) {
                delta_cache_size -= trg_entry->delta_size;
                free(trg_entry->delta_data);
        }
        trg_entry->delta_data = 0;
        trg_entry->delta = src_entry;
        trg_entry->delta_size = delta_size;
        trg_entry->depth = src_entry->depth + 1;

        if (delta_cacheable(src, trg, src_size, trg_size, delta_size)) {
                trg_entry->delta_data = xrealloc(delta_buf, delta_size);
                delta_cache_size += trg_entry->delta_size;
        } else
                free(delta_buf);
        return 1;
}

static unsigned int check_delta_limit(struct object_entry *me, unsigned int n)
{
        struct object_entry *child = me->delta_child;
        unsigned int m = n;
        while (child) {
                unsigned int c = check_delta_limit(child, n + 1);
                if (m < c)
                        m = c;
                child = child->delta_sibling;
        }
        return m;
}

static void 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;
        int max_depth;

        if (!nr_objects)
                return;
        array = xmalloc(array_size);
        memset(array, 0, array_size);
        if (progress)
                start_progress(&progress_state, "Deltifying %u objects...", "", nr_result);

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

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

                if (progress)
                        display_progress(&progress_state, processed);

                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;

                if (entry->no_try_delta)
                        continue;

                free_delta_index(n->index);
                n->index = NULL;
                free(n->data);
                n->data = NULL;
                n->entry = entry;

                /*
                 * 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.
                 */
                max_depth = depth;
                if (entry->delta_child) {
                        max_depth -= check_delta_limit(entry, 0);
                        if (max_depth <= 0)
                                goto next;
                }

                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, max_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;

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

        if (progress)
                stop_progress(&progress_state);

        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)
{
        struct object_entry **delta_list;
        uint32_t i;

        get_object_details();

        if (!window || !depth)
                return;

        delta_list = xmalloc(nr_objects * sizeof(*delta_list));
        for (i = 0; i < nr_objects; i++)
                delta_list[i] = objects + i;
        qsort(delta_list, nr_objects, sizeof(*delta_list), type_size_sort);
        find_deltas(delta_list, window+1, depth);
        free(delta_list);
}

static int git_pack_config(const char *k, const char *v)
{
        if(!strcmp(k, "pack.window")) {
                window = git_config_int(k, v);
                return 0;
        }
        if(!strcmp(k, "pack.depth")) {
                depth = git_config_int(k, v);
                return 0;
        }
        if (!strcmp(k, "pack.compression")) {
                int level = git_config_int(k, v);
                if (level == -1)
                        level = Z_DEFAULT_COMPRESSION;
                else if (level < 0 || level > Z_BEST_COMPRESSION)
                        die("bad pack compression level %d", level);
                pack_compression_level = level;
                pack_compression_seen = 1;
                return 0;
        }
        if (!strcmp(k, "pack.deltacachesize")) {
                max_delta_cache_size = 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];

        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);

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

static void show_commit(struct commit *commit)
{
        add_object_entry(commit->object.sha1, OBJ_COMMIT, NULL, 0);
}

static void show_object(struct object_array_entry *p)
{
        add_preferred_base_object(p->name);
        add_object_entry(p->item->sha1, p->item->type, p->name, 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);
}

static int adjust_perm(const char *path, mode_t mode)
{
        if (chmod(path, mode))
                return -1;
        return adjust_shared_perm(path);
}

int cmd_pack_objects(int argc, const char **argv, const char *prefix)
{
        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);
        if (!pack_compression_seen && core_compression_seen)
                pack_compression_level = core_compression_level;

        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, "--compression=")) {
                        char *end;
                        int level = strtoul(arg+14, &end, 0);
                        if (!arg[14] || *end)
                                usage(pack_usage);
                        if (level == -1)
                                level = Z_DEFAULT_COMPRESSION;
                        else if (level < 0 || level > Z_BEST_COMPRESSION)
                                die("bad pack compression level %d", level);
                        pack_compression_level = level;
                        continue;
                }
                if (!prefixcmp(arg, "--max-pack-size=")) {
                        char *end;
                        pack_size_limit = strtoul(arg+16, &end, 0) * 1024 * 1024;
                        if (!arg[16] || *end)
                                usage(pack_usage);
                        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("--no-reuse-object", arg)) {
                        no_reuse_object = 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;
                }
                if (!prefixcmp(arg, "--index-version=")) {
                        char *c;
                        index_default_version = strtoul(arg + 16, &c, 10);
                        if (index_default_version > 2)
                                die("bad %s", arg);
                        if (*c == ',')
                                index_off32_limit = strtoul(c+1, &c, 0);
                        if (*c || index_off32_limit & 0x80000000)
                                die("bad %s", arg);
                        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 && pack_size_limit)
                die("--max-pack-size cannot be used to build a pack for transfer.");

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

        prepare_packed_git();

        if (progress)
                start_progress(&progress_state, "Generating pack...",
                               "Counting objects: ", 0);
        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) {
                stop_progress(&progress_state);
                fprintf(stderr, "Done counting %u objects.\n", nr_objects);
        }

        if (non_empty && !nr_result)
                return 0;
        if (progress && (nr_objects != nr_result))
                fprintf(stderr, "Result has %u objects.\n", nr_result);
        if (nr_result)
                prepare_pack(window, depth);
        write_pack_file();
        if (progress)
                fprintf(stderr, "Total %u (delta %u), reused %u (delta %u)\n",
                        written, written_delta, reused, reused_delta);
        return 0;
}