]> git.ipfire.org Git - thirdparty/git.git/blob - bloom.c
clone: allow "--bare" with "-o"
[thirdparty/git.git] / bloom.c
1 #include "git-compat-util.h"
2 #include "bloom.h"
3 #include "diff.h"
4 #include "diffcore.h"
5 #include "revision.h"
6 #include "hashmap.h"
7 #include "commit-graph.h"
8 #include "commit.h"
9
10 define_commit_slab(bloom_filter_slab, struct bloom_filter);
11
12 static struct bloom_filter_slab bloom_filters;
13
14 struct pathmap_hash_entry {
15 struct hashmap_entry entry;
16 const char path[FLEX_ARRAY];
17 };
18
19 static uint32_t rotate_left(uint32_t value, int32_t count)
20 {
21 uint32_t mask = 8 * sizeof(uint32_t) - 1;
22 count &= mask;
23 return ((value << count) | (value >> ((-count) & mask)));
24 }
25
26 static inline unsigned char get_bitmask(uint32_t pos)
27 {
28 return ((unsigned char)1) << (pos & (BITS_PER_WORD - 1));
29 }
30
31 static int load_bloom_filter_from_graph(struct commit_graph *g,
32 struct bloom_filter *filter,
33 uint32_t graph_pos)
34 {
35 uint32_t lex_pos, start_index, end_index;
36
37 while (graph_pos < g->num_commits_in_base)
38 g = g->base_graph;
39
40 /* The commit graph commit 'c' lives in doesn't carry Bloom filters. */
41 if (!g->chunk_bloom_indexes)
42 return 0;
43
44 lex_pos = graph_pos - g->num_commits_in_base;
45
46 end_index = get_be32(g->chunk_bloom_indexes + 4 * lex_pos);
47
48 if (lex_pos > 0)
49 start_index = get_be32(g->chunk_bloom_indexes + 4 * (lex_pos - 1));
50 else
51 start_index = 0;
52
53 filter->len = end_index - start_index;
54 filter->data = (unsigned char *)(g->chunk_bloom_data +
55 sizeof(unsigned char) * start_index +
56 BLOOMDATA_CHUNK_HEADER_SIZE);
57
58 return 1;
59 }
60
61 /*
62 * Calculate the murmur3 32-bit hash value for the given data
63 * using the given seed.
64 * Produces a uniformly distributed hash value.
65 * Not considered to be cryptographically secure.
66 * Implemented as described in https://en.wikipedia.org/wiki/MurmurHash#Algorithm
67 */
68 uint32_t murmur3_seeded(uint32_t seed, const char *data, size_t len)
69 {
70 const uint32_t c1 = 0xcc9e2d51;
71 const uint32_t c2 = 0x1b873593;
72 const uint32_t r1 = 15;
73 const uint32_t r2 = 13;
74 const uint32_t m = 5;
75 const uint32_t n = 0xe6546b64;
76 int i;
77 uint32_t k1 = 0;
78 const char *tail;
79
80 int len4 = len / sizeof(uint32_t);
81
82 uint32_t k;
83 for (i = 0; i < len4; i++) {
84 uint32_t byte1 = (uint32_t)data[4*i];
85 uint32_t byte2 = ((uint32_t)data[4*i + 1]) << 8;
86 uint32_t byte3 = ((uint32_t)data[4*i + 2]) << 16;
87 uint32_t byte4 = ((uint32_t)data[4*i + 3]) << 24;
88 k = byte1 | byte2 | byte3 | byte4;
89 k *= c1;
90 k = rotate_left(k, r1);
91 k *= c2;
92
93 seed ^= k;
94 seed = rotate_left(seed, r2) * m + n;
95 }
96
97 tail = (data + len4 * sizeof(uint32_t));
98
99 switch (len & (sizeof(uint32_t) - 1)) {
100 case 3:
101 k1 ^= ((uint32_t)tail[2]) << 16;
102 /*-fallthrough*/
103 case 2:
104 k1 ^= ((uint32_t)tail[1]) << 8;
105 /*-fallthrough*/
106 case 1:
107 k1 ^= ((uint32_t)tail[0]) << 0;
108 k1 *= c1;
109 k1 = rotate_left(k1, r1);
110 k1 *= c2;
111 seed ^= k1;
112 break;
113 }
114
115 seed ^= (uint32_t)len;
116 seed ^= (seed >> 16);
117 seed *= 0x85ebca6b;
118 seed ^= (seed >> 13);
119 seed *= 0xc2b2ae35;
120 seed ^= (seed >> 16);
121
122 return seed;
123 }
124
125 void fill_bloom_key(const char *data,
126 size_t len,
127 struct bloom_key *key,
128 const struct bloom_filter_settings *settings)
129 {
130 int i;
131 const uint32_t seed0 = 0x293ae76f;
132 const uint32_t seed1 = 0x7e646e2c;
133 const uint32_t hash0 = murmur3_seeded(seed0, data, len);
134 const uint32_t hash1 = murmur3_seeded(seed1, data, len);
135
136 key->hashes = (uint32_t *)xcalloc(settings->num_hashes, sizeof(uint32_t));
137 for (i = 0; i < settings->num_hashes; i++)
138 key->hashes[i] = hash0 + i * hash1;
139 }
140
141 void clear_bloom_key(struct bloom_key *key)
142 {
143 FREE_AND_NULL(key->hashes);
144 }
145
146 void add_key_to_filter(const struct bloom_key *key,
147 struct bloom_filter *filter,
148 const struct bloom_filter_settings *settings)
149 {
150 int i;
151 uint64_t mod = filter->len * BITS_PER_WORD;
152
153 for (i = 0; i < settings->num_hashes; i++) {
154 uint64_t hash_mod = key->hashes[i] % mod;
155 uint64_t block_pos = hash_mod / BITS_PER_WORD;
156
157 filter->data[block_pos] |= get_bitmask(hash_mod);
158 }
159 }
160
161 void init_bloom_filters(void)
162 {
163 init_bloom_filter_slab(&bloom_filters);
164 }
165
166 static int pathmap_cmp(const void *hashmap_cmp_fn_data,
167 const struct hashmap_entry *eptr,
168 const struct hashmap_entry *entry_or_key,
169 const void *keydata)
170 {
171 const struct pathmap_hash_entry *e1, *e2;
172
173 e1 = container_of(eptr, const struct pathmap_hash_entry, entry);
174 e2 = container_of(entry_or_key, const struct pathmap_hash_entry, entry);
175
176 return strcmp(e1->path, e2->path);
177 }
178
179 static void init_truncated_large_filter(struct bloom_filter *filter)
180 {
181 filter->data = xmalloc(1);
182 filter->data[0] = 0xFF;
183 filter->len = 1;
184 }
185
186 struct bloom_filter *get_or_compute_bloom_filter(struct repository *r,
187 struct commit *c,
188 int compute_if_not_present,
189 const struct bloom_filter_settings *settings,
190 enum bloom_filter_computed *computed)
191 {
192 struct bloom_filter *filter;
193 int i;
194 struct diff_options diffopt;
195
196 if (computed)
197 *computed = BLOOM_NOT_COMPUTED;
198
199 if (!bloom_filters.slab_size)
200 return NULL;
201
202 filter = bloom_filter_slab_at(&bloom_filters, c);
203
204 if (!filter->data) {
205 uint32_t graph_pos;
206 if (repo_find_commit_pos_in_graph(r, c, &graph_pos))
207 load_bloom_filter_from_graph(r->objects->commit_graph,
208 filter, graph_pos);
209 }
210
211 if (filter->data && filter->len)
212 return filter;
213 if (!compute_if_not_present)
214 return NULL;
215
216 repo_diff_setup(r, &diffopt);
217 diffopt.flags.recursive = 1;
218 diffopt.detect_rename = 0;
219 diffopt.max_changes = settings->max_changed_paths;
220 diff_setup_done(&diffopt);
221
222 /* ensure commit is parsed so we have parent information */
223 repo_parse_commit(r, c);
224
225 if (c->parents)
226 diff_tree_oid(&c->parents->item->object.oid, &c->object.oid, "", &diffopt);
227 else
228 diff_tree_oid(NULL, &c->object.oid, "", &diffopt);
229 diffcore_std(&diffopt);
230
231 if (diff_queued_diff.nr <= settings->max_changed_paths) {
232 struct hashmap pathmap = HASHMAP_INIT(pathmap_cmp, NULL);
233 struct pathmap_hash_entry *e;
234 struct hashmap_iter iter;
235
236 for (i = 0; i < diff_queued_diff.nr; i++) {
237 const char *path = diff_queued_diff.queue[i]->two->path;
238
239 /*
240 * Add each leading directory of the changed file, i.e. for
241 * 'dir/subdir/file' add 'dir' and 'dir/subdir' as well, so
242 * the Bloom filter could be used to speed up commands like
243 * 'git log dir/subdir', too.
244 *
245 * Note that directories are added without the trailing '/'.
246 */
247 do {
248 char *last_slash = strrchr(path, '/');
249
250 FLEX_ALLOC_STR(e, path, path);
251 hashmap_entry_init(&e->entry, strhash(path));
252
253 if (!hashmap_get(&pathmap, &e->entry, NULL))
254 hashmap_add(&pathmap, &e->entry);
255 else
256 free(e);
257
258 if (!last_slash)
259 last_slash = (char*)path;
260 *last_slash = '\0';
261
262 } while (*path);
263
264 diff_free_filepair(diff_queued_diff.queue[i]);
265 }
266
267 if (hashmap_get_size(&pathmap) > settings->max_changed_paths) {
268 init_truncated_large_filter(filter);
269 if (computed)
270 *computed |= BLOOM_TRUNC_LARGE;
271 goto cleanup;
272 }
273
274 filter->len = (hashmap_get_size(&pathmap) * settings->bits_per_entry + BITS_PER_WORD - 1) / BITS_PER_WORD;
275 if (!filter->len) {
276 if (computed)
277 *computed |= BLOOM_TRUNC_EMPTY;
278 filter->len = 1;
279 }
280 CALLOC_ARRAY(filter->data, filter->len);
281
282 hashmap_for_each_entry(&pathmap, &iter, e, entry) {
283 struct bloom_key key;
284 fill_bloom_key(e->path, strlen(e->path), &key, settings);
285 add_key_to_filter(&key, filter, settings);
286 clear_bloom_key(&key);
287 }
288
289 cleanup:
290 hashmap_clear_and_free(&pathmap, struct pathmap_hash_entry, entry);
291 } else {
292 for (i = 0; i < diff_queued_diff.nr; i++)
293 diff_free_filepair(diff_queued_diff.queue[i]);
294 init_truncated_large_filter(filter);
295
296 if (computed)
297 *computed |= BLOOM_TRUNC_LARGE;
298 }
299
300 if (computed)
301 *computed |= BLOOM_COMPUTED;
302
303 free(diff_queued_diff.queue);
304 DIFF_QUEUE_CLEAR(&diff_queued_diff);
305
306 return filter;
307 }
308
309 int bloom_filter_contains(const struct bloom_filter *filter,
310 const struct bloom_key *key,
311 const struct bloom_filter_settings *settings)
312 {
313 int i;
314 uint64_t mod = filter->len * BITS_PER_WORD;
315
316 if (!mod)
317 return -1;
318
319 for (i = 0; i < settings->num_hashes; i++) {
320 uint64_t hash_mod = key->hashes[i] % mod;
321 uint64_t block_pos = hash_mod / BITS_PER_WORD;
322 if (!(filter->data[block_pos] & get_bitmask(hash_mod)))
323 return 0;
324 }
325
326 return 1;
327 }