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git/bloom.c

327 lines
8.0 KiB

#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,
const struct hashmap_entry *eptr,
const struct hashmap_entry *entry_or_key,
const void *keydata)
{
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;
}