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/*
* Authored by Alex Hultman, 2018-2022.
* Intellectual property of third-party.
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* http://www.apache.org/licenses/LICENSE-2.0
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef UWS_BLOOMFILTER_H
#define UWS_BLOOMFILTER_H
/* This filter has no false positives or collisions for the standard
* and non-standard common request headers */
#include <string_view>
#include <bitset>
namespace uWS {
struct BloomFilter {
private:
std::bitset<256> filter;
static inline uint32_t perfectHash(uint32_t features) {
return features *= 1843993368;
}
union ScrambleArea {
unsigned char p[4];
uint32_t val;
};
ScrambleArea getFeatures(std::string_view key) {
ScrambleArea s;
s.p[0] = reinterpret_cast<const unsigned char&>(key[0]);
s.p[1] = reinterpret_cast<const unsigned char&>(key[key.length() - 1]);
s.p[2] = reinterpret_cast<const unsigned char&>(key[key.length() - 2]);
s.p[3] = reinterpret_cast<const unsigned char&>(key[key.length() >> 1]);
return s;
}
public:
bool mightHave(std::string_view key) {
if (key.length() < 2) {
return true;
}
ScrambleArea s = getFeatures(key);
s.val = perfectHash(s.val);
return filter[s.p[0]] &&
filter[s.p[1]] &&
filter[s.p[2]] &&
filter[s.p[3]];
}
void add(std::string_view key) {
if (key.length() >= 2) {
ScrambleArea s = getFeatures(key);
s.val = perfectHash(s.val);
filter[s.p[0]] = 1;
filter[s.p[1]] = 1;
filter[s.p[2]] = 1;
filter[s.p[3]] = 1;
}
}
void reset() {
filter.reset();
}
};
}
#endif // UWS_BLOOMFILTER_H