virtual bool KeyMayMatch(const Slice& key, const Slice& bloom_filter) const {
const size_t len = bloom_filter.size();
if (len < 2) return false;
const char* array = bloom_filter.data();
const size_t bits = (len - 1) * 8;
// Use the encoded k so that we can read filters generated by
// bloom filters created using different parameters.
const size_t k = array[len-1];
if (k > 30) {
// Reserved for potentially new encodings for short bloom filters.
// Consider it a match.
return true;
}
uint32_t h = BloomHash(key);
const uint32_t delta = (h >> 17) | (h << 15); // Rotate right 17 bits
for (size_t j = 0; j < k; j++) {
const uint32_t bitpos = h % bits;
if ((array[bitpos/8] & (1 << (bitpos % 8))) == 0) return false;
h += delta;
}
return true;
}
bool BloomFilter::Match(const string &key)
{
uint32_t h = BloomHash(key);
const uint32_t delta = (h>>17) | (h<<15);
for (size_t i = 0; i < bits_per_key_; i ++) {
const uint32_t bitpos = h % bits_;
if ((array_[bitpos/8] & (1<<(bitpos%8))) == 0) return false;
h += delta;
}
return true;
}
int BloomFilter::AddKey(const string &key)
{
// Use double-hashing to generate a sequence of hash values.
// See analysis in [Kirsch,Mitzenmacher 2006].
uint32_t h = BloomHash(key);
const uint32_t delta = (h>>17) | (h<<15);
for (size_t i = 0; i < bits_per_key_; i ++) {
const uint32_t bitpos = h % bits_;
array_[bitpos/8] |= (1<<(bitpos%8));
h += delta;
}
return 0;
}
