bloom.h

   1 #ifndef BLOOM_H
   2 #define BLOOM_H
   3
   4 struct commit;
   5 struct repository;
   6
   7 struct bloom_filter_settings {
   8         /*
   9          * The version of the hashing technique being used.
  10          * We currently only support version = 1 which is
  11          * the seeded murmur3 hashing technique implemented
  12          * in bloom.c.
  13          */
  14         uint32_t hash_version;
  15
  16         /*
  17          * The number of times a path is hashed, i.e. the
  18          * number of bit positions tht cumulatively
  19          * determine whether a path is present in the
  20          * Bloom filter.
  21          */
  22         uint32_t num_hashes;
  23
  24         /*
  25          * The minimum number of bits per entry in the Bloom
  26          * filter. If the filter contains 'n' entries, then
  27          * filter size is the minimum number of 8-bit words
  28          * that contain n*b bits.
  29          */
  30         uint32_t bits_per_entry;
  31 };
  32
  33 #define DEFAULT_BLOOM_FILTER_SETTINGS { 1, 7, 10 }
  34 #define BITS_PER_WORD 8
  35 #define BLOOMDATA_CHUNK_HEADER_SIZE 3 * sizeof(uint32_t)
  36
  37 /*
  38  * A bloom_filter struct represents a data segment to
  39  * use when testing hash values. The 'len' member
  40  * dictates how many entries are stored in
  41  * 'data'.
  42  */
  43 struct bloom_filter {
  44         unsigned char *data;
  45         size_t len;
  46 };
  47
  48 /*
  49  * A bloom_key represents the k hash values for a
  50  * given string. These can be precomputed and
  51  * stored in a bloom_key for re-use when testing
  52  * against a bloom_filter. The number of hashes is
  53  * given by the Bloom filter settings and is the same
  54  * for all Bloom filters and keys interacting with
  55  * the loaded version of the commit graph file and
  56  * the Bloom data chunks.
  57  */
  58 struct bloom_key {
  59         uint32_t *hashes;
  60 };
  61
  62 /*
  63  * Calculate the murmur3 32-bit hash value for the given data
  64  * using the given seed.
  65  * Produces a uniformly distributed hash value.
  66  * Not considered to be cryptographically secure.
  67  * Implemented as described in https://en.wikipedia.org/wiki/MurmurHash#Algorithm
  68  */
  69 uint32_t murmur3_seeded(uint32_t seed, const char *data, size_t len);
  70
  71 void fill_bloom_key(const char *data,
  72                     size_t len,
  73                     struct bloom_key *key,
  74                     const struct bloom_filter_settings *settings);
  75
  76 void add_key_to_filter(const struct bloom_key *key,
  77                                            struct bloom_filter *filter,
  78                                            const struct bloom_filter_settings *settings);
  79
  80 void init_bloom_filters(void);
  81
  82 struct bloom_filter *get_bloom_filter(struct repository *r,
  83                                       struct commit *c,
  84                                       int compute_if_not_present);
  85
  86 int bloom_filter_contains(const struct bloom_filter *filter,
  87                           const struct bloom_key *key,
  88                           const struct bloom_filter_settings *settings);
  89
  90 #endif