diff options
Diffstat (limited to 'bloom.c')
| -rw-r--r-- | bloom.c | 327 |
1 files changed, 327 insertions, 0 deletions
@@ -0,0 +1,327 @@ +#include "git-compat-util.h" +#include "bloom.h" +#include "diff.h" +#include "diffcore.h" +#include "revision.h" +#include "hashmap.h" +#include "commit-graph.h" +#include "commit.h" + +define_commit_slab(bloom_filter_slab, struct bloom_filter); + +static struct bloom_filter_slab bloom_filters; + +struct pathmap_hash_entry { + struct hashmap_entry entry; + const char path[FLEX_ARRAY]; +}; + +static uint32_t rotate_left(uint32_t value, int32_t count) +{ + uint32_t mask = 8 * sizeof(uint32_t) - 1; + count &= mask; + return ((value << count) | (value >> ((-count) & mask))); +} + +static inline unsigned char get_bitmask(uint32_t pos) +{ + return ((unsigned char)1) << (pos & (BITS_PER_WORD - 1)); +} + +static int load_bloom_filter_from_graph(struct commit_graph *g, + struct bloom_filter *filter, + uint32_t graph_pos) +{ + uint32_t lex_pos, start_index, end_index; + + while (graph_pos < g->num_commits_in_base) + g = g->base_graph; + + /* The commit graph commit 'c' lives in doesn't carry Bloom filters. */ + if (!g->chunk_bloom_indexes) + return 0; + + lex_pos = graph_pos - g->num_commits_in_base; + + end_index = get_be32(g->chunk_bloom_indexes + 4 * lex_pos); + + if (lex_pos > 0) + start_index = get_be32(g->chunk_bloom_indexes + 4 * (lex_pos - 1)); + else + start_index = 0; + + filter->len = end_index - start_index; + filter->data = (unsigned char *)(g->chunk_bloom_data + + sizeof(unsigned char) * start_index + + BLOOMDATA_CHUNK_HEADER_SIZE); + + return 1; +} + +/* + * Calculate the murmur3 32-bit hash value for the given data + * using the given seed. + * Produces a uniformly distributed hash value. + * Not considered to be cryptographically secure. + * Implemented as described in https://en.wikipedia.org/wiki/MurmurHash#Algorithm + */ +uint32_t murmur3_seeded(uint32_t seed, const char *data, size_t len) +{ + const uint32_t c1 = 0xcc9e2d51; + const uint32_t c2 = 0x1b873593; + const uint32_t r1 = 15; + const uint32_t r2 = 13; + const uint32_t m = 5; + const uint32_t n = 0xe6546b64; + int i; + uint32_t k1 = 0; + const char *tail; + + int len4 = len / sizeof(uint32_t); + + uint32_t k; + for (i = 0; i < len4; i++) { + uint32_t byte1 = (uint32_t)data[4*i]; + uint32_t byte2 = ((uint32_t)data[4*i + 1]) << 8; + uint32_t byte3 = ((uint32_t)data[4*i + 2]) << 16; + uint32_t byte4 = ((uint32_t)data[4*i + 3]) << 24; + k = byte1 | byte2 | byte3 | byte4; + k *= c1; + k = rotate_left(k, r1); + k *= c2; + + seed ^= k; + seed = rotate_left(seed, r2) * m + n; + } + + tail = (data + len4 * sizeof(uint32_t)); + + switch (len & (sizeof(uint32_t) - 1)) { + case 3: + k1 ^= ((uint32_t)tail[2]) << 16; + /*-fallthrough*/ + case 2: + k1 ^= ((uint32_t)tail[1]) << 8; + /*-fallthrough*/ + case 1: + k1 ^= ((uint32_t)tail[0]) << 0; + k1 *= c1; + k1 = rotate_left(k1, r1); + k1 *= c2; + seed ^= k1; + break; + } + + seed ^= (uint32_t)len; + seed ^= (seed >> 16); + seed *= 0x85ebca6b; + seed ^= (seed >> 13); + seed *= 0xc2b2ae35; + seed ^= (seed >> 16); + + return seed; +} + +void fill_bloom_key(const char *data, + size_t len, + struct bloom_key *key, + const struct bloom_filter_settings *settings) +{ + int i; + const uint32_t seed0 = 0x293ae76f; + const uint32_t seed1 = 0x7e646e2c; + const uint32_t hash0 = murmur3_seeded(seed0, data, len); + const uint32_t hash1 = murmur3_seeded(seed1, data, len); + + key->hashes = (uint32_t *)xcalloc(settings->num_hashes, sizeof(uint32_t)); + for (i = 0; i < settings->num_hashes; i++) + key->hashes[i] = hash0 + i * hash1; +} + +void clear_bloom_key(struct bloom_key *key) +{ + FREE_AND_NULL(key->hashes); +} + +void add_key_to_filter(const struct bloom_key *key, + struct bloom_filter *filter, + const struct bloom_filter_settings *settings) +{ + int i; + uint64_t mod = filter->len * BITS_PER_WORD; + + for (i = 0; i < settings->num_hashes; i++) { + uint64_t hash_mod = key->hashes[i] % mod; + uint64_t block_pos = hash_mod / BITS_PER_WORD; + + filter->data[block_pos] |= get_bitmask(hash_mod); + } +} + +void init_bloom_filters(void) +{ + init_bloom_filter_slab(&bloom_filters); +} + +static int pathmap_cmp(const void *hashmap_cmp_fn_data UNUSED, + const struct hashmap_entry *eptr, + const struct hashmap_entry *entry_or_key, + const void *keydata UNUSED) +{ + const struct pathmap_hash_entry *e1, *e2; + + e1 = container_of(eptr, const struct pathmap_hash_entry, entry); + e2 = container_of(entry_or_key, const struct pathmap_hash_entry, entry); + + return strcmp(e1->path, e2->path); +} + +static void init_truncated_large_filter(struct bloom_filter *filter) +{ + filter->data = xmalloc(1); + filter->data[0] = 0xFF; + filter->len = 1; +} + +struct bloom_filter *get_or_compute_bloom_filter(struct repository *r, + struct commit *c, + int compute_if_not_present, + const struct bloom_filter_settings *settings, + enum bloom_filter_computed *computed) +{ + struct bloom_filter *filter; + int i; + struct diff_options diffopt; + + if (computed) + *computed = BLOOM_NOT_COMPUTED; + + if (!bloom_filters.slab_size) + return NULL; + + filter = bloom_filter_slab_at(&bloom_filters, c); + + if (!filter->data) { + uint32_t graph_pos; + if (repo_find_commit_pos_in_graph(r, c, &graph_pos)) + load_bloom_filter_from_graph(r->objects->commit_graph, + filter, graph_pos); + } + + if (filter->data && filter->len) + return filter; + if (!compute_if_not_present) + return NULL; + + repo_diff_setup(r, &diffopt); + diffopt.flags.recursive = 1; + diffopt.detect_rename = 0; + diffopt.max_changes = settings->max_changed_paths; + diff_setup_done(&diffopt); + + /* ensure commit is parsed so we have parent information */ + repo_parse_commit(r, c); + + if (c->parents) + diff_tree_oid(&c->parents->item->object.oid, &c->object.oid, "", &diffopt); + else + diff_tree_oid(NULL, &c->object.oid, "", &diffopt); + diffcore_std(&diffopt); + + if (diff_queued_diff.nr <= settings->max_changed_paths) { + struct hashmap pathmap = HASHMAP_INIT(pathmap_cmp, NULL); + struct pathmap_hash_entry *e; + struct hashmap_iter iter; + + for (i = 0; i < diff_queued_diff.nr; i++) { + const char *path = diff_queued_diff.queue[i]->two->path; + + /* + * Add each leading directory of the changed file, i.e. for + * 'dir/subdir/file' add 'dir' and 'dir/subdir' as well, so + * the Bloom filter could be used to speed up commands like + * 'git log dir/subdir', too. + * + * Note that directories are added without the trailing '/'. + */ + do { + char *last_slash = strrchr(path, '/'); + + FLEX_ALLOC_STR(e, path, path); + hashmap_entry_init(&e->entry, strhash(path)); + + if (!hashmap_get(&pathmap, &e->entry, NULL)) + hashmap_add(&pathmap, &e->entry); + else + free(e); + + if (!last_slash) + last_slash = (char*)path; + *last_slash = '\0'; + + } while (*path); + + diff_free_filepair(diff_queued_diff.queue[i]); + } + + if (hashmap_get_size(&pathmap) > settings->max_changed_paths) { + init_truncated_large_filter(filter); + if (computed) + *computed |= BLOOM_TRUNC_LARGE; + goto cleanup; + } + + filter->len = (hashmap_get_size(&pathmap) * settings->bits_per_entry + BITS_PER_WORD - 1) / BITS_PER_WORD; + if (!filter->len) { + if (computed) + *computed |= BLOOM_TRUNC_EMPTY; + filter->len = 1; + } + CALLOC_ARRAY(filter->data, filter->len); + + hashmap_for_each_entry(&pathmap, &iter, e, entry) { + struct bloom_key key; + fill_bloom_key(e->path, strlen(e->path), &key, settings); + add_key_to_filter(&key, filter, settings); + clear_bloom_key(&key); + } + + cleanup: + hashmap_clear_and_free(&pathmap, struct pathmap_hash_entry, entry); + } else { + for (i = 0; i < diff_queued_diff.nr; i++) + diff_free_filepair(diff_queued_diff.queue[i]); + init_truncated_large_filter(filter); + + if (computed) + *computed |= BLOOM_TRUNC_LARGE; + } + + if (computed) + *computed |= BLOOM_COMPUTED; + + free(diff_queued_diff.queue); + DIFF_QUEUE_CLEAR(&diff_queued_diff); + + return filter; +} + +int bloom_filter_contains(const struct bloom_filter *filter, + const struct bloom_key *key, + const struct bloom_filter_settings *settings) +{ + int i; + uint64_t mod = filter->len * BITS_PER_WORD; + + if (!mod) + return -1; + + for (i = 0; i < settings->num_hashes; i++) { + uint64_t hash_mod = key->hashes[i] % mod; + uint64_t block_pos = hash_mod / BITS_PER_WORD; + if (!(filter->data[block_pos] & get_bitmask(hash_mod))) + return 0; + } + + return 1; +} |