patch-ids.c

   1 #include "cache.h"
   2 #include "diff.h"
   3 #include "commit.h"
   4 #include "patch-ids.h"
   5
   6 static int commit_patch_id(struct commit *commit, struct diff_options *options,
   7                     unsigned char *sha1)
   8 {
   9         if (commit->parents)
  10                 diff_tree_sha1(commit->parents->item->object.sha1,
  11                                commit->object.sha1, "", options);
  12         else
  13                 diff_root_tree_sha1(commit->object.sha1, "", options);
  14         diffcore_std(options);
  15         return diff_flush_patch_id(options, sha1);
  16 }
  17
  18 static uint32_t take2(const unsigned char *id)
  19 {
  20         return ((id[0] << 8) | id[1]);
  21 }
  22
  23 /*
  24  * Conventional binary search loop looks like this:
  25  *
  26  *      do {
  27  *              int mi = (lo + hi) / 2;
  28  *              int cmp = "entry pointed at by mi" minus "target";
  29  *              if (!cmp)
  30  *                      return (mi is the wanted one)
  31  *              if (cmp > 0)
  32  *                      hi = mi; "mi is larger than target"
  33  *              else
  34  *                      lo = mi+1; "mi is smaller than target"
  35  *      } while (lo < hi);
  36  *
  37  * The invariants are:
  38  *
  39  * - When entering the loop, lo points at a slot that is never
  40  *   above the target (it could be at the target), hi points at a
  41  *   slot that is guaranteed to be above the target (it can never
  42  *   be at the target).
  43  *
  44  * - We find a point 'mi' between lo and hi (mi could be the same
  45  *   as lo, but never can be the same as hi), and check if it hits
  46  *   the target.  There are three cases:
  47  *
  48  *    - if it is a hit, we are happy.
  49  *
  50  *    - if it is strictly higher than the target, we update hi with
  51  *      it.
  52  *
  53  *    - if it is strictly lower than the target, we update lo to be
  54  *      one slot after it, because we allow lo to be at the target.
  55  *
  56  * When choosing 'mi', we do not have to take the "middle" but
  57  * anywhere in between lo and hi, as long as lo <= mi < hi is
  58  * satisfied.  When we somehow know that the distance between the
  59  * target and lo is much shorter than the target and hi, we could
  60  * pick mi that is much closer to lo than the midway.
  61  */
  62 static int patch_pos(struct patch_id **table, int nr, const unsigned char *id)
  63 {
  64         int hi = nr;
  65         int lo = 0;
  66         int mi = 0;
  67
  68         if (!nr)
  69                 return -1;
  70
  71         if (nr != 1) {
  72                 unsigned lov, hiv, miv, ofs;
  73
  74                 for (ofs = 0; ofs < 18; ofs += 2) {
  75                         lov = take2(table[0]->patch_id + ofs);
  76                         hiv = take2(table[nr-1]->patch_id + ofs);
  77                         miv = take2(id + ofs);
  78                         if (miv < lov)
  79                                 return -1;
  80                         if (hiv < miv)
  81                                 return -1 - nr;
  82                         if (lov != hiv) {
  83                                 /*
  84                                  * At this point miv could be equal
  85                                  * to hiv (but id could still be higher);
  86                                  * the invariant of (mi < hi) should be
  87                                  * kept.
  88                                  */
  89                                 mi = (nr-1) * (miv - lov) / (hiv - lov);
  90                                 if (lo <= mi && mi < hi)
  91                                         break;
  92                                 die("oops");
  93                         }
  94                 }
  95                 if (18 <= ofs)
  96                         die("cannot happen -- lo and hi are identical");
  97         }
  98
  99         do {
 100                 int cmp;
 101                 cmp = hashcmp(table[mi]->patch_id, id);
 102                 if (!cmp)
 103                         return mi;
 104                 if (cmp > 0)
 105                         hi = mi;
 106                 else
 107                         lo = mi + 1;
 108                 mi = (hi + lo) / 2;
 109         } while (lo < hi);
 110         return -lo-1;
 111 }
 112
 113 #define BUCKET_SIZE 190 /* 190 * 21 = 3990, with slop close enough to 4K */
 114 struct patch_id_bucket {
 115         struct patch_id_bucket *next;
 116         int nr;
 117         struct patch_id bucket[BUCKET_SIZE];
 118 };
 119
 120 int init_patch_ids(struct patch_ids *ids)
 121 {
 122         memset(ids, 0, sizeof(*ids));
 123         diff_setup(&ids->diffopts);
 124         ids->diffopts.recursive = 1;
 125         if (diff_setup_done(&ids->diffopts) < 0)
 126                 return error("diff_setup_done failed");
 127         return 0;
 128 }
 129
 130 int free_patch_ids(struct patch_ids *ids)
 131 {
 132         struct patch_id_bucket *next, *patches;
 133
 134         free(ids->table);
 135         for (patches = ids->patches; patches; patches = next) {
 136                 next = patches->next;
 137                 free(patches);
 138         }
 139         return 0;
 140 }
 141
 142 static struct patch_id *add_commit(struct commit *commit,
 143                                    struct patch_ids *ids,
 144                                    int no_add)
 145 {
 146         struct patch_id_bucket *bucket;
 147         struct patch_id *ent;
 148         unsigned char sha1[20];
 149         int pos;
 150
 151         if (commit_patch_id(commit, &ids->diffopts, sha1))
 152                 return NULL;
 153         pos = patch_pos(ids->table, ids->nr, sha1);
 154         if (0 <= pos)
 155                 return ids->table[pos];
 156         if (no_add)
 157                 return NULL;
 158
 159         pos = -1 - pos;
 160
 161         bucket = ids->patches;
 162         if (!bucket || (BUCKET_SIZE <= bucket->nr)) {
 163                 bucket = xcalloc(1, sizeof(*bucket));
 164                 bucket->next = ids->patches;
 165                 ids->patches = bucket;
 166         }
 167         ent = &bucket->bucket[bucket->nr++];
 168         hashcpy(ent->patch_id, sha1);
 169
 170         if (ids->alloc <= ids->nr) {
 171                 ids->alloc = alloc_nr(ids->nr);
 172                 ids->table = xrealloc(ids->table, sizeof(ent) * ids->alloc);
 173         }
 174         if (pos < ids->nr)
 175                 memmove(ids->table + pos + 1, ids->table + pos,
 176                         sizeof(ent) * (ids->nr - pos));
 177         ids->nr++;
 178         ids->table[pos] = ent;
 179         return ids->table[pos];
 180 }
 181
 182 struct patch_id *has_commit_patch_id(struct commit *commit,
 183                                      struct patch_ids *ids)
 184 {
 185         return add_commit(commit, ids, 1);
 186 }
 187
 188 struct patch_id *add_commit_patch_id(struct commit *commit,
 189                                      struct patch_ids *ids)
 190 {
 191         return add_commit(commit, ids, 0);
 192 }