_ Git - dnsseed-rust/blob - src/bloom.rs

   1 use std::collections::hash_map::RandomState;
   2 use std::hash::{BuildHasher, Hash, Hasher};
   3 use std::time::{Duration, Instant};
   4 use std::marker::PhantomData;
   5
   6 // Constants for roughly 1 in 1 million fp with 18m entries
   7 /// Number of entries in the filter (each 4 bits). 256MiB in total.
   8 const FILTER_SIZE: usize = 64 * 1024 * 1024 * 8;
   9 const HASHES: usize = 27;
  10 const ROLL_COUNT: usize = 1_240_000;
  11 #[cfg(test)]
  12 const GENERATION_BITS: usize = 2;
  13 #[cfg(not(test))]
  14 const GENERATION_BITS: usize = 4;
  15 pub const GENERATION_COUNT: usize = (1 << GENERATION_BITS) - 1;
  16 const ELEMENTS_PER_BYTE: usize = 8 / GENERATION_BITS;
  17
  18 pub struct RollingBloomFilter<T: Hash> {
  19         last_roll: Instant,
  20         inserted_in_last_generations: [usize; GENERATION_COUNT - 1],
  21         inserted_since_last_roll: usize,
  22         current_generation: u8,
  23         bits: Vec<u8>,
  24         hash_keys: [RandomState; HASHES],
  25         _entry_type: PhantomData<T>,
  26 }
  27
  28 impl<T: Hash> RollingBloomFilter<T> {
  29         pub fn new() -> Self {
  30                 let mut bits = Vec::new();
  31                 bits.resize(FILTER_SIZE * GENERATION_BITS / 8, 0);
  32                 Self {
  33                         last_roll: Instant::now(),
  34                         inserted_since_last_roll: 0,
  35                         inserted_in_last_generations: [0; GENERATION_COUNT - 1],
  36                         current_generation: 1,
  37                         bits,
  38                         hash_keys: [RandomState::new(), RandomState::new(), RandomState::new(), RandomState::new(), RandomState::new(),
  39                                     RandomState::new(), RandomState::new(), RandomState::new(), RandomState::new(), RandomState::new(),
  40                                     RandomState::new(), RandomState::new(), RandomState::new(), RandomState::new(), RandomState::new(),
  41                                     RandomState::new(), RandomState::new(), RandomState::new(), RandomState::new(), RandomState::new(),
  42                                     RandomState::new(), RandomState::new(), RandomState::new(), RandomState::new(), RandomState::new(),
  43                                     RandomState::new(), RandomState::new()],
  44                         _entry_type: PhantomData,
  45                 }
  46         }
  47
  48         pub fn contains(&self, item: &T) -> bool {
  49                 for state in self.hash_keys.iter() {
  50                         let mut hasher = state.build_hasher();
  51                         item.hash(&mut hasher);
  52                         let idx = hasher.finish() as usize;
  53
  54                         let byte = self.bits[(idx / ELEMENTS_PER_BYTE) % (FILTER_SIZE / 8)];
  55                         let bits_shift = (idx % ELEMENTS_PER_BYTE) * GENERATION_BITS;
  56                         let bits = (byte & ((GENERATION_COUNT as u8) << bits_shift)) >> bits_shift;
  57                         if bits == 0 { return false; }
  58                 }
  59                 true
  60         }
  61
  62         pub fn get_element_count(&self) -> [usize; GENERATION_COUNT] {
  63                 let mut res = [0; GENERATION_COUNT];
  64                 res[0..(GENERATION_COUNT-1)].copy_from_slice(&self.inserted_in_last_generations);
  65                 *res.last_mut().unwrap() = self.inserted_since_last_roll;
  66                 res
  67         }
  68
  69         pub fn insert(&mut self, item: &T, roll_duration: Duration) {
  70                 if Instant::now() - self.last_roll > roll_duration / GENERATION_COUNT as u32 ||
  71                    self.inserted_since_last_roll > ROLL_COUNT {
  72                         self.current_generation += 1;
  73                         if self.current_generation == GENERATION_COUNT as u8 + 1 { self.current_generation = 1; }
  74                         let remove_generation = self.current_generation;
  75
  76                         for idx in 0..FILTER_SIZE {
  77                                 let byte = &mut self.bits[(idx / ELEMENTS_PER_BYTE) % (FILTER_SIZE / 8)];
  78                                 let bits_shift = (idx % ELEMENTS_PER_BYTE) * GENERATION_BITS;
  79                                 let bits = (*byte & ((GENERATION_COUNT as u8) << bits_shift)) >> bits_shift;
  80
  81                                 if bits == remove_generation {
  82                                         *byte &= !((GENERATION_COUNT as u8) << bits_shift);
  83                                 }
  84                         }
  85                         self.last_roll = Instant::now();
  86                         let mut new_generations = [0; GENERATION_COUNT - 1];
  87                         new_generations[0..GENERATION_COUNT - 2].copy_from_slice(&self.inserted_in_last_generations[1..]);
  88                         new_generations[GENERATION_COUNT - 2] = self.inserted_since_last_roll;
  89                         self.inserted_in_last_generations = new_generations;
  90                         self.inserted_since_last_roll = 0;
  91                 }
  92
  93                 for state in self.hash_keys.iter() {
  94                         let mut hasher = state.build_hasher();
  95                         item.hash(&mut hasher);
  96                         let idx = hasher.finish() as usize;
  97
  98                         let byte = &mut self.bits[(idx / ELEMENTS_PER_BYTE) % (FILTER_SIZE / 8)];
  99                         let bits_shift = (idx % ELEMENTS_PER_BYTE) * GENERATION_BITS;
 100                         *byte &= !((GENERATION_COUNT as u8) << bits_shift);
 101                         *byte |= self.current_generation << bits_shift;
 102                 }
 103                 self.inserted_since_last_roll += 1;
 104         }
 105 }
 106
 107 #[test]
 108 fn test_bloom() {
 109         let mut filter = RollingBloomFilter::new();
 110         for i in 0..1000 {
 111                 filter.insert(&i, Duration::from_secs(60 * 60 * 24));
 112         }
 113         for i in 0..1000 {
 114                 assert!(filter.contains(&i));
 115         }
 116         for i in 1000..2000 {
 117                 assert!(!filter.contains(&i));
 118         }
 119         assert_eq!(filter.get_element_count(), [0, 0, 1000]);
 120         filter.inserted_since_last_roll = ROLL_COUNT + 1;
 121         filter.insert(&1000, Duration::from_secs(60 * 60 * 24));
 122         assert_eq!(filter.get_element_count(), [0, ROLL_COUNT + 1, 1]);
 123         for i in 0..1001 {
 124                 assert!(filter.contains(&i));
 125         }
 126         filter.inserted_since_last_roll = ROLL_COUNT + 1;
 127         for i in 1001..2000 {
 128                 filter.insert(&i, Duration::from_secs(60 * 60 * 24));
 129         }
 130         assert_eq!(filter.get_element_count(), [ROLL_COUNT + 1, ROLL_COUNT + 1, 999]);
 131         for i in 0..2000 {
 132                 assert!(filter.contains(&i));
 133         }
 134         filter.inserted_since_last_roll = ROLL_COUNT + 1;
 135         filter.insert(&2000, Duration::from_secs(60 * 60 * 24));
 136         assert_eq!(filter.get_element_count(), [ROLL_COUNT + 1, ROLL_COUNT + 1, 1]);
 137         for i in 0..1000 {
 138                 assert!(!filter.contains(&i));
 139         }
 140         for i in 1000..2001 {
 141                 assert!(filter.contains(&i));
 142         }
 143 }