Andrew's git - gitweb.git/blob

   1#include "cache.h"
   2#include "pack-revindex.h"
   3
   4/*
   5 * Pack index for existing packs give us easy access to the offsets into
   6 * corresponding pack file where each object's data starts, but the entries
   7 * do not store the size of the compressed representation (uncompressed
   8 * size is easily available by examining the pack entry header).  It is
   9 * also rather expensive to find the sha1 for an object given its offset.
  10 *
  11 * We build a hashtable of existing packs (pack_revindex), and keep reverse
  12 * index here -- pack index file is sorted by object name mapping to offset;
  13 * this pack_revindex[].revindex array is a list of offset/index_nr pairs
  14 * ordered by offset, so if you know the offset of an object, next offset
  15 * is where its packed representation ends and the index_nr can be used to
  16 * get the object sha1 from the main index.
  17 */
  18
  19struct pack_revindex {
  20        struct packed_git *p;
  21        struct revindex_entry *revindex;
  22};
  23
  24static struct pack_revindex *pack_revindex;
  25static int pack_revindex_hashsz;
  26
  27static int pack_revindex_ix(struct packed_git *p)
  28{
  29        unsigned long ui = (unsigned long)p;
  30        int i;
  31
  32        ui = ui ^ (ui >> 16); /* defeat structure alignment */
  33        i = (int)(ui % pack_revindex_hashsz);
  34        while (pack_revindex[i].p) {
  35                if (pack_revindex[i].p == p)
  36                        return i;
  37                if (++i == pack_revindex_hashsz)
  38                        i = 0;
  39        }
  40        return -1 - i;
  41}
  42
  43static void init_pack_revindex(void)
  44{
  45        int num;
  46        struct packed_git *p;
  47
  48        for (num = 0, p = packed_git; p; p = p->next)
  49                num++;
  50        if (!num)
  51                return;
  52        pack_revindex_hashsz = num * 11;
  53        pack_revindex = xcalloc(sizeof(*pack_revindex), pack_revindex_hashsz);
  54        for (p = packed_git; p; p = p->next) {
  55                num = pack_revindex_ix(p);
  56                num = - 1 - num;
  57                pack_revindex[num].p = p;
  58        }
  59        /* revindex elements are lazily initialized */
  60}
  61
  62static int cmp_offset(const void *a_, const void *b_)
  63{
  64        const struct revindex_entry *a = a_;
  65        const struct revindex_entry *b = b_;
  66        return (a->offset < b->offset) ? -1 : (a->offset > b->offset) ? 1 : 0;
  67}
  68
  69/*
  70 * Ordered list of offsets of objects in the pack.
  71 */
  72static void create_pack_revindex(struct pack_revindex *rix)
  73{
  74        struct packed_git *p = rix->p;
  75        int num_ent = p->num_objects;
  76        int i;
  77        const char *index = p->index_data;
  78
  79        rix->revindex = xmalloc(sizeof(*rix->revindex) * (num_ent + 1));
  80        index += 4 * 256;
  81
  82        if (p->index_version > 1) {
  83                const uint32_t *off_32 =
  84                        (uint32_t *)(index + 8 + p->num_objects * (20 + 4));
  85                const uint32_t *off_64 = off_32 + p->num_objects;
  86                for (i = 0; i < num_ent; i++) {
  87                        uint32_t off = ntohl(*off_32++);
  88                        if (!(off & 0x80000000)) {
  89                                rix->revindex[i].offset = off;
  90                        } else {
  91                                rix->revindex[i].offset =
  92                                        ((uint64_t)ntohl(*off_64++)) << 32;
  93                                rix->revindex[i].offset |=
  94                                        ntohl(*off_64++);
  95                        }
  96                        rix->revindex[i].nr = i;
  97                }
  98        } else {
  99                for (i = 0; i < num_ent; i++) {
 100                        uint32_t hl = *((uint32_t *)(index + 24 * i));
 101                        rix->revindex[i].offset = ntohl(hl);
 102                        rix->revindex[i].nr = i;
 103                }
 104        }
 105
 106        /* This knows the pack format -- the 20-byte trailer
 107         * follows immediately after the last object data.
 108         */
 109        rix->revindex[num_ent].offset = p->pack_size - 20;
 110        rix->revindex[num_ent].nr = -1;
 111        qsort(rix->revindex, num_ent, sizeof(*rix->revindex), cmp_offset);
 112}
 113
 114struct revindex_entry *find_pack_revindex(struct packed_git *p, off_t ofs)
 115{
 116        int num;
 117        int lo, hi;
 118        struct pack_revindex *rix;
 119        struct revindex_entry *revindex;
 120
 121        if (!pack_revindex_hashsz)
 122                init_pack_revindex();
 123        num = pack_revindex_ix(p);
 124        if (num < 0)
 125                die("internal error: pack revindex fubar");
 126
 127        rix = &pack_revindex[num];
 128        if (!rix->revindex)
 129                create_pack_revindex(rix);
 130        revindex = rix->revindex;
 131
 132        lo = 0;
 133        hi = p->num_objects + 1;
 134        do {
 135                int mi = (lo + hi) / 2;
 136                if (revindex[mi].offset == ofs) {
 137                        return revindex + mi;
 138                } else if (ofs < revindex[mi].offset)
 139                        hi = mi;
 140                else
 141                        lo = mi + 1;
 142        } while (lo < hi);
 143        die("internal error: pack revindex corrupt");
 144}