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Randomize hash value and optimize bucket calculation.

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This commit is contained in:
levlam 2022-02-23 16:27:19 +03:00
parent b3a784f4ba
commit 73ade8cc43
2 changed files with 18 additions and 12 deletions
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3
tdutils/td/utils/FlatHashMapChunks.h
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@ -483,8 +483,7 @@ class FlatHashTableChunks {
}
HashInfo calc_hash(const KeyT &key) {
auto h = HashT()(key);
// TODO: will be problematic with current hash.
auto h = randomize_hash(HashT()(key));
return {(h >> 8) % chunks_.size(), static_cast<uint8>(0x80 | h)};
}

27
tdutils/td/utils/FlatHashMapLinear.h
View File

@ -18,12 +18,22 @@
#include <utility>
namespace td {
// TODO: move
template <class KeyT>
bool is_key_empty(const KeyT &key) {
return key == KeyT();
}
inline uint32 randomize_hash(size_t h) {
auto result = static_cast<uint32>(h & 0xFFFFFFFF);
result ^= result >> 16;
result *= 0x85ebca6b;
result ^= result >> 13;
result *= 0xc2b2ae35;
result ^= result >> 16;
return result;
}
template <class KeyT, class ValueT>
struct MapNode {
using first_type = KeyT;
@ -485,8 +495,8 @@ class FlatHashTable {
resize(want_size);
}
size_t calc_bucket(const KeyT &key) const {
return HashT()(key) % nodes_.size();
uint32 calc_bucket(const KeyT &key) const {
return randomize_hash(HashT()(key)) & static_cast<uint32>(nodes_.size() - 1);
}
void resize(size_t new_size) {
@ -497,7 +507,7 @@ class FlatHashTable {
if (old_node.empty()) {
continue;
}
size_t bucket = calc_bucket(old_node.key());
auto bucket = calc_bucket(old_node.key());
while (!nodes_[bucket].empty()) {
next_bucket(bucket);
}
@ -505,11 +515,8 @@ class FlatHashTable {
}
}
void next_bucket(size_t &bucket) const {
bucket++;
if (unlikely(bucket == nodes_.size())) {
bucket = 0;
}
void next_bucket(uint32 &bucket) const {
bucket = (bucket + 1) & static_cast<uint32>(nodes_.size() - 1);
}
void erase_node(NodeIterator it) {
@ -531,7 +538,7 @@ class FlatHashTable {
auto want_i = calc_bucket(nodes_[test_bucket].key());
if (want_i < empty_i) {
want_i += nodes_.size();
want_i += static_cast<uint32>(nodes_.size());
}
if (want_i <= empty_i || want_i > test_i) {