ZYM/BH-Bookstore-2023
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upd: optimize hash to avoid being hacked

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ZhuangYumin
2023-12-08 01:20:12 +00:00
parent 0dfaa80f87
commit c874b6df24
1 changed files with 27 additions and 7 deletions
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34
backend/include/key2index.hpp
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@ -14,16 +14,36 @@ class String2Index {
constexpr static char salt2[10] = "9B<mF_me"; constexpr static char salt2[10] = "9B<mF_me";
constexpr static char sub_salt1[10] = "23333"; constexpr static char sub_salt1[10] = "23333";
constexpr static char sub_salt2[10] = "..."; constexpr static char sub_salt2[10] = "...";
constexpr static char inner_salt[17] = "si9aW@zl#2$3%4^!";
static inline size_t Hash(std::string str) noexcept { typedef unsigned long long hash_t;
static_assert(sizeof(hash_t) == 8);
static inline hash_t Hash(std::string str) noexcept {
/* Reference: http://xorshift.di.unimi.it/splitmix64.c */
str = salt1 + str + salt2; str = salt1 + str + salt2;
size_t ret = 0; hash_t ret = 0;
for (int i = 0; i < str.length(); ++i) ret = ret * 131 + str[i]; int i;
for (; i + 8 <= str.length(); i += 8) {
ret ^= *reinterpret_cast<const hash_t *>(str.c_str() + i);
ret ^= *reinterpret_cast<const hash_t *>(inner_salt + (i & 15));
ret += 0x9e3779b97f4a7c15;
ret = (ret ^ (ret >> 30)) * 0xbf58476d1ce4e5b9;
ret = (ret ^ (ret >> 27)) * 0x94d049bb133111eb;
ret ^= ret >> 31;
}
for (; i < str.length(); ++i) {
ret ^= str[i];
ret ^= inner_salt[i & 15];
ret += 0x9e3779b97f4a7c15;
ret = (ret ^ (ret >> 30)) * 0xbf58476d1ce4e5b9;
ret = (ret ^ (ret >> 27)) * 0x94d049bb133111eb;
ret ^= ret >> 31;
}
return ret; return ret;
} }
struct Node { struct Node {
size_t main_hash, sub_hash; hash_t main_hash, sub_hash;
int val, nxt_idx = 0; int val, nxt_idx = 0;
Node() = default; Node() = default;
Node(std::string str, int _val) Node(std::string str, int _val)
@ -70,7 +90,7 @@ class String2Index {
} }
} }
void Insert(const std::string &str, int val) noexcept { void Insert(const std::string &str, int val) noexcept {
size_t hash_val = Hash(str); hash_t hash_val = Hash(str);
int idx = hash_table[hash_val % kBucketSize]; int idx = hash_table[hash_val % kBucketSize];
Node nd(str, val); Node nd(str, val);
if (idx == 0) { if (idx == 0) {
@ -83,7 +103,7 @@ class String2Index {
} }
} }
void Delete(const std::string &str, int val) noexcept { void Delete(const std::string &str, int val) noexcept {
size_t str_main_hash = Hash(str), hash_t str_main_hash = Hash(str),
str_sub_hash = Hash(sub_salt1 + str + sub_salt2); str_sub_hash = Hash(sub_salt1 + str + sub_salt2);
int idx = hash_table[str_main_hash % kBucketSize]; int idx = hash_table[str_main_hash % kBucketSize];
Node nd, last_nd; Node nd, last_nd;
@ -109,7 +129,7 @@ class String2Index {
} }
std::vector<int> Find(const std::string &str) noexcept { std::vector<int> Find(const std::string &str) noexcept {
std::vector<int> ret; std::vector<int> ret;
size_t str_main_hash = Hash(str), hash_t str_main_hash = Hash(str),
str_sub_hash = Hash(sub_salt1 + str + sub_salt2); str_sub_hash = Hash(sub_salt1 + str + sub_salt2);
int idx = hash_table[str_main_hash % kBucketSize]; int idx = hash_table[str_main_hash % kBucketSize];
Node nd; Node nd;