git.oblomov.eu Git - git/blob - 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 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                                    struct commit *c)
  34 {
  35         uint32_t lex_pos, start_index, end_index;
  36
  37         while (c->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 = c->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 add_key_to_filter(const struct bloom_key *key,
 142                                            struct bloom_filter *filter,
 143                                            const struct bloom_filter_settings *settings)
 144 {
 145         int i;
 146         uint64_t mod = filter->len * BITS_PER_WORD;
 147
 148         for (i = 0; i < settings->num_hashes; i++) {
 149                 uint64_t hash_mod = key->hashes[i] % mod;
 150                 uint64_t block_pos = hash_mod / BITS_PER_WORD;
 151
 152                 filter->data[block_pos] |= get_bitmask(hash_mod);
 153         }
 154 }
 155
 156 void init_bloom_filters(void)
 157 {
 158         init_bloom_filter_slab(&bloom_filters);
 159 }
 160
 161 struct bloom_filter *get_bloom_filter(struct repository *r,
 162                                       struct commit *c,
 163                                           int compute_if_not_present)
 164 {
 165         struct bloom_filter *filter;
 166         struct bloom_filter_settings settings = DEFAULT_BLOOM_FILTER_SETTINGS;
 167         int i;
 168         struct diff_options diffopt;
 169         int max_changes = 512;
 170
 171         if (bloom_filters.slab_size == 0)
 172                 return NULL;
 173
 174         filter = bloom_filter_slab_at(&bloom_filters, c);
 175
 176         if (!filter->data) {
 177                 load_commit_graph_info(r, c);
 178                 if (c->graph_pos != COMMIT_NOT_FROM_GRAPH &&
 179                         r->objects->commit_graph->chunk_bloom_indexes) {
 180                         if (load_bloom_filter_from_graph(r->objects->commit_graph, filter, c))
 181                                 return filter;
 182                         else
 183                                 return NULL;
 184                 }
 185         }
 186
 187         if (filter->data || !compute_if_not_present)
 188                 return filter;
 189
 190         repo_diff_setup(r, &diffopt);
 191         diffopt.flags.recursive = 1;
 192         diffopt.detect_rename = 0;
 193         diffopt.max_changes = max_changes;
 194         diff_setup_done(&diffopt);
 195
 196         if (c->parents)
 197                 diff_tree_oid(&c->parents->item->object.oid, &c->object.oid, "", &diffopt);
 198         else
 199                 diff_tree_oid(NULL, &c->object.oid, "", &diffopt);
 200         diffcore_std(&diffopt);
 201
 202         if (diff_queued_diff.nr <= max_changes) {
 203                 struct hashmap pathmap;
 204                 struct pathmap_hash_entry *e;
 205                 struct hashmap_iter iter;
 206                 hashmap_init(&pathmap, NULL, NULL, 0);
 207
 208                 for (i = 0; i < diff_queued_diff.nr; i++) {
 209                         const char *path = diff_queued_diff.queue[i]->two->path;
 210
 211                         /*
 212                         * Add each leading directory of the changed file, i.e. for
 213                         * 'dir/subdir/file' add 'dir' and 'dir/subdir' as well, so
 214                         * the Bloom filter could be used to speed up commands like
 215                         * 'git log dir/subdir', too.
 216                         *
 217                         * Note that directories are added without the trailing '/'.
 218                         */
 219                         do {
 220                                 char *last_slash = strrchr(path, '/');
 221
 222                                 FLEX_ALLOC_STR(e, path, path);
 223                                 hashmap_entry_init(&e->entry, strhash(path));
 224                                 hashmap_add(&pathmap, &e->entry);
 225
 226                                 if (!last_slash)
 227                                         last_slash = (char*)path;
 228                                 *last_slash = '\0';
 229
 230                         } while (*path);
 231
 232                         diff_free_filepair(diff_queued_diff.queue[i]);
 233                 }
 234
 235                 filter->len = (hashmap_get_size(&pathmap) * settings.bits_per_entry + BITS_PER_WORD - 1) / BITS_PER_WORD;
 236                 filter->data = xcalloc(filter->len, sizeof(unsigned char));
 237
 238                 hashmap_for_each_entry(&pathmap, &iter, e, entry) {
 239                         struct bloom_key key;
 240                         fill_bloom_key(e->path, strlen(e->path), &key, &settings);
 241                         add_key_to_filter(&key, filter, &settings);
 242                 }
 243
 244                 hashmap_free_entries(&pathmap, struct pathmap_hash_entry, entry);
 245         } else {
 246                 for (i = 0; i < diff_queued_diff.nr; i++)
 247                         diff_free_filepair(diff_queued_diff.queue[i]);
 248                 filter->data = NULL;
 249                 filter->len = 0;
 250         }
 251
 252         free(diff_queued_diff.queue);
 253         DIFF_QUEUE_CLEAR(&diff_queued_diff);
 254
 255         return filter;
 256 }
 257
 258 int bloom_filter_contains(const struct bloom_filter *filter,
 259                           const struct bloom_key *key,
 260                           const struct bloom_filter_settings *settings)
 261 {
 262         int i;
 263         uint64_t mod = filter->len * BITS_PER_WORD;
 264
 265         if (!mod)
 266                 return -1;
 267
 268         for (i = 0; i < settings->num_hashes; i++) {
 269                 uint64_t hash_mod = key->hashes[i] % mod;
 270                 uint64_t block_pos = hash_mod / BITS_PER_WORD;
 271                 if (!(filter->data[block_pos] & get_bitmask(hash_mod)))
 272                         return 0;
 273         }
 274
 275         return 1;
 276 }