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Improved bloom filter

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This commit is contained in:
uNetworkingAB
2022-10-29 06:18:17 +02:00
committed by GitHub
parent 3f72aea565
commit a730941806
1 changed files with 33 additions and 18 deletions
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src/BloomFilter.h
+33 -18
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@@ -1,5 +1,5 @@
/* /*
* Authored by Alex Hultman, 2018-2019. * Authored by Alex Hultman, 2018-2022.
* Intellectual property of third-party. * Intellectual property of third-party.
* Licensed under the Apache License, Version 2.0 (the "License"); * Licensed under the Apache License, Version 2.0 (the "License");
@@ -18,8 +18,8 @@
#ifndef UWS_BLOOMFILTER_H #ifndef UWS_BLOOMFILTER_H
#define UWS_BLOOMFILTER_H #define UWS_BLOOMFILTER_H
/* This filter has a decently low amount of false positives for the /* This filter has no false positives or collisions for the standard
* standard and non-standard common request headers */ * and non-standard common request headers */
#include <string_view> #include <string_view>
#include <bitset> #include <bitset>
@@ -28,32 +28,47 @@ namespace uWS {
struct BloomFilter { struct BloomFilter {
private: private:
std::bitset<512> filter; std::bitset<256> filter;
static inline uint32_t perfectHash(uint32_t features) {
unsigned int hash1(std::string_view key) { return features *= 1843993368;
return ((size_t)key[key.length() - 1] - (key.length() << 3)) & 511;
} }
unsigned int hash2(std::string_view key) { union ScrambleArea {
return (((size_t)key[0] + (key.length() << 4)) & 511); unsigned char p[4];
} uint32_t val;
};
unsigned int hash3(std::string_view key) { ScrambleArea getFeatures(std::string_view key) {
return ((unsigned int)key[key.length() - 2] - 97 - (key.length() << 5)) & 511; ScrambleArea s;
s.p[0] = key[0];
s.p[1] = key[key.length() - 1];
s.p[2] = key[key.length() - 2];
s.p[3] = key[key.length() >> 1];
return s;
} }
public: public:
bool mightHave(std::string_view key) { bool mightHave(std::string_view key) {
return !key.length() || (filter.test(hash1(key)) && filter.test(hash2(key)) && (key.length() < 2 || filter.test(hash3(key)))); if (key.length() < 2) {
return true;
}
ScrambleArea s = getFeatures(key);
s.val = perfectHash(s.val);
return filter.test(s.p[0]) &
filter.test(s.p[1]) &
filter.test(s.p[2]) &
filter.test(s.p[3]);
} }
void add(std::string_view key) { void add(std::string_view key) {
if (key.length()) {
filter.set(hash1(key));
filter.set(hash2(key));
}
if (key.length() >= 2) { if (key.length() >= 2) {
filter.set(hash3(key)); ScrambleArea s = getFeatures(key);
s.val = perfectHash(s.val);
filter.set(s.p[0]);
filter.set(s.p[1]);
filter.set(s.p[2]);
filter.set(s.p[3]);
} }
} }