git-instaweb: improve auto-discovery of httpd and call conventions.
[git] / 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         DIFF_OPT_SET(&ids->diffopts, RECURSIVE);
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 }