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updated OAHashMap to use robinhood hashing

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This commit is contained in:
karroffel 2018-05-03 14:40:55 +02:00
parent 2e474f42b8
commit bf24d570bb
5 changed files with 196 additions and 463 deletions
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645
core/oa_hash_map.h
View file

@ -36,176 +36,181 @@
#include "os/copymem.h"
#include "os/memory.h"
// uncomment this to disable initial local storage.
#define OA_HASH_MAP_INITIAL_LOCAL_STORAGE
/**
* This class implements a hash map datastructure that uses open addressing with
* local probing.
*
* It can give huge performance improvements over a chained HashMap because of
* the increased data locality.
*
* Because of that locality property it's important to not use "large" value
* types as the "TData" type. If TData values are too big it can cause more
* cache misses then chaining. If larger values are needed then storing those
* in a separate array and using pointers or indices to reference them is the
* better solution.
*
* This hash map also implements real-time incremental rehashing.
* A HashMap implementation that uses open addressing with robinhood hashing.
* Robinhood hashing swaps out entries that have a smaller probing distance
* than the to-be-inserted entry, that evens out the average probing distance
* and enables faster lookups.
*
* The entries are stored inplace, so huge keys or values might fill cache lines
* a lot faster.
*/
template <class TKey, class TData,
uint16_t INITIAL_NUM_ELEMENTS = 64,
template <class TKey, class TValue,
class Hasher = HashMapHasherDefault,
class Comparator = HashMapComparatorDefault<TKey> >
class OAHashMap {
private:
#ifdef OA_HASH_MAP_INITIAL_LOCAL_STORAGE
TData local_data[INITIAL_NUM_ELEMENTS];
TKey local_keys[INITIAL_NUM_ELEMENTS];
uint32_t local_hashes[INITIAL_NUM_ELEMENTS];
uint8_t local_flags[INITIAL_NUM_ELEMENTS / 4 + (INITIAL_NUM_ELEMENTS % 4 != 0 ? 1 : 0)];
#endif
TValue *values;
TKey *keys;
uint32_t *hashes;
struct {
TData *data;
TKey *keys;
uint32_t *hashes;
uint32_t capacity;
// This is actually an array of bits, 4 bit pairs per octet.
// | ba ba ba ba | ba ba ba ba | ....
//
// if a is set it means that there is an element present.
// if b is set it means that an element was deleted. This is needed for
// the local probing to work without relocating any succeeding and
// colliding entries.
uint8_t *flags;
uint32_t num_elements;
uint32_t capacity;
} table, old_table;
static const uint32_t EMPTY_HASH = 0;
static const uint32_t DELETED_HASH_BIT = 1 << 31;
bool is_rehashing;
uint32_t rehash_position;
uint32_t rehash_amount;
_FORCE_INLINE_ uint32_t _hash(const TKey &p_key) {
uint32_t hash = Hasher::hash(p_key);
uint32_t elements;
if (hash == EMPTY_HASH) {
hash = EMPTY_HASH + 1;
} else if (hash & DELETED_HASH_BIT) {
hash &= ~DELETED_HASH_BIT;
}
/* Methods */
return hash;
}
// returns true if the value already existed, false if it's a new entry
bool _raw_set_with_hash(uint32_t p_hash, const TKey &p_key, const TData &p_data) {
for (int i = 0; i < table.capacity; i++) {
_FORCE_INLINE_ uint32_t _get_probe_length(uint32_t p_pos, uint32_t p_hash) {
p_hash = p_hash & ~DELETED_HASH_BIT; // we don't care if it was deleted or not
int pos = (p_hash + i) % table.capacity;
uint32_t original_pos = p_hash % capacity;
int flags_pos = pos / 4;
int flags_pos_offset = pos % 4;
return p_pos - original_pos;
}
bool is_filled_flag = table.flags[flags_pos] & (1 << (2 * flags_pos_offset));
bool is_deleted_flag = table.flags[flags_pos] & (1 << (2 * flags_pos_offset + 1));
_FORCE_INLINE_ void _construct(uint32_t p_pos, uint32_t p_hash, const TKey &p_key, const TValue &p_value) {
memnew_placement(&keys[p_pos], TKey(p_key));
memnew_placement(&values[p_pos], TValue(p_value));
hashes[p_pos] = p_hash;
if (is_filled_flag) {
if (table.hashes[pos] == p_hash && Comparator::compare(table.keys[pos], p_key)) {
table.data[pos] = p_data;
return true;
num_elements++;
}
bool _lookup_pos(const TKey &p_key, uint32_t &r_pos) {
uint32_t hash = _hash(p_key);
uint32_t pos = hash % capacity;
uint32_t distance = 0;
while (42) {
if (hashes[pos] == EMPTY_HASH) {
return false;
}
if (distance > _get_probe_length(pos, hashes[pos])) {
return false;
}
if (hashes[pos] == hash && Comparator::compare(keys[pos], p_key)) {
r_pos = pos;
return true;
}
pos = (pos + 1) % capacity;
distance++;
}
}
void _insert_with_hash(uint32_t p_hash, const TKey &p_key, const TValue &p_value) {
uint32_t hash = p_hash;
uint32_t distance = 0;
uint32_t pos = hash % capacity;
TKey key = p_key;
TValue value = p_value;
while (42) {
if (hashes[pos] == EMPTY_HASH) {
_construct(pos, hash, p_key, p_value);
return;
}
// not an empty slot, let's check the probing length of the existing one
uint32_t existing_probe_len = _get_probe_length(pos, hashes[pos]);
if (existing_probe_len < distance) {
if (hashes[pos] & DELETED_HASH_BIT) {
// we found a place where we can fit in!
_construct(pos, hash, p_key, p_value);
return;
}
SWAP(hash, hashes[pos]);
SWAP(key, keys[pos]);
SWAP(value, values[pos]);
distance = existing_probe_len;
}
pos = (pos + 1) % capacity;
distance++;
}
}
void _resize_and_rehash() {
TKey *old_keys = keys;
TValue *old_values = values;
uint32_t *old_hashes = hashes;
uint32_t old_capacity = capacity;
capacity = old_capacity * 2;
num_elements = 0;
keys = memnew_arr(TKey, capacity);
values = memnew_arr(TValue, capacity);
hashes = memnew_arr(uint32_t, capacity);
for (int i = 0; i < capacity; i++) {
hashes[i] = 0;
}
for (uint32_t i = 0; i < old_capacity; i++) {
if (old_hashes[i] == EMPTY_HASH) {
continue;
}
if (old_hashes[i] & DELETED_HASH_BIT) {
continue;
}
table.keys[pos] = p_key;
table.data[pos] = p_data;
table.hashes[pos] = p_hash;
table.flags[flags_pos] |= (1 << (2 * flags_pos_offset));
table.flags[flags_pos] &= ~(1 << (2 * flags_pos_offset + 1));
return false;
_insert_with_hash(old_hashes[i], old_keys[i], old_values[i]);
}
return false;
memdelete_arr(old_keys);
memdelete_arr(old_values);
memdelete_arr(old_hashes);
}
public:
_FORCE_INLINE_ uint32_t get_capacity() const { return table.capacity; }
_FORCE_INLINE_ uint32_t get_num_elements() const { return elements; }
_FORCE_INLINE_ uint32_t get_capacity() const { return capacity; }
_FORCE_INLINE_ uint32_t get_num_elements() const { return num_elements; }
void set(const TKey &p_key, const TData &p_data) {
void insert(const TKey &p_key, const TValue &p_value) {
uint32_t hash = Hasher::hash(p_key);
// We don't progress the rehashing if the table just got resized
// to keep the cost of this function low.
if (is_rehashing) {
// rehash progress
for (int i = 0; i <= rehash_amount && rehash_position < old_table.capacity; rehash_position++) {
int flags_pos = rehash_position / 4;
int flags_pos_offset = rehash_position % 4;
bool is_filled_flag = (old_table.flags[flags_pos] & (1 << (2 * flags_pos_offset))) > 0;
bool is_deleted_flag = (old_table.flags[flags_pos] & (1 << (2 * flags_pos_offset + 1))) > 0;
if (is_filled_flag) {
_raw_set_with_hash(old_table.hashes[rehash_position], old_table.keys[rehash_position], old_table.data[rehash_position]);
old_table.keys[rehash_position].~TKey();
old_table.data[rehash_position].~TData();
memnew_placement(&old_table.keys[rehash_position], TKey);
memnew_placement(&old_table.data[rehash_position], TData);
old_table.flags[flags_pos] &= ~(1 << (2 * flags_pos_offset));
old_table.flags[flags_pos] |= (1 << (2 * flags_pos_offset + 1));
}
}
if (rehash_position >= old_table.capacity) {
// wohooo, we can get rid of the old table.
is_rehashing = false;
#ifdef OA_HASH_MAP_INITIAL_LOCAL_STORAGE
if (old_table.data == local_data) {
// Everything is local, so no cleanup :P
} else
#endif
{
memdelete_arr(old_table.data);
memdelete_arr(old_table.keys);
memdelete_arr(old_table.hashes);
memdelete_arr(old_table.flags);
}
}
if ((float)num_elements / (float)capacity > 0.9) {
_resize_and_rehash();
}
// Table is almost full, resize and start rehashing process.
if (elements >= table.capacity * 0.7) {
uint32_t hash = _hash(p_key);
old_table.capacity = table.capacity;
old_table.data = table.data;
old_table.flags = table.flags;
old_table.hashes = table.hashes;
old_table.keys = table.keys;
_insert_with_hash(hash, p_key, p_value);
}
table.capacity = old_table.capacity * 2;
void set(const TKey &p_key, const TValue &p_data) {
uint32_t pos = 0;
bool exists = _lookup_pos(p_key, pos);
table.data = memnew_arr(TData, table.capacity);
table.flags = memnew_arr(uint8_t, table.capacity / 4 + (table.capacity % 4 != 0 ? 1 : 0));
table.hashes = memnew_arr(uint32_t, table.capacity);
table.keys = memnew_arr(TKey, table.capacity);
zeromem(table.flags, table.capacity / 4 + (table.capacity % 4 != 0 ? 1 : 0));
is_rehashing = true;
rehash_position = 0;
rehash_amount = (elements * 2) / (table.capacity * 0.7 - old_table.capacity);
if (exists) {
values[pos].~TValue();
memnew_placement(&values[pos], TValue(p_data));
} else {
insert(p_key, p_data);
}
if (!_raw_set_with_hash(hash, p_key, p_data))
elements++;
}
/**
@ -214,380 +219,108 @@ public:
* if r_data is not NULL then the value will be written to the object
* it points to.
*/
bool lookup(const TKey &p_key, TData *r_data) {
bool lookup(const TKey &p_key, TValue &r_data) {
uint32_t pos = 0;
bool exists = _lookup_pos(p_key, pos);
uint32_t hash = Hasher::hash(p_key);
bool check_old_table = is_rehashing;
bool check_new_table = true;
// search for the key and return the value associated with it
//
// if we're rehashing we need to check both the old and the
// current table. If we find a value in the old table we still
// need to continue searching in the new table as it might have
// been added after
TData *value = NULL;
for (int i = 0; i < table.capacity; i++) {
if (!check_new_table && !check_old_table) {
break;
}
// if we're rehashing check the old table
if (check_old_table && i < old_table.capacity) {
int pos = (hash + i) % old_table.capacity;
int flags_pos = pos / 4;
int flags_pos_offset = pos % 4;
bool is_filled_flag = (old_table.flags[flags_pos] & (1 << (2 * flags_pos_offset))) > 0;
bool is_deleted_flag = (old_table.flags[flags_pos] & (1 << (2 * flags_pos_offset + 1))) > 0;
if (is_filled_flag) {
// found our entry?
if (old_table.hashes[pos] == hash && Comparator::compare(old_table.keys[pos], p_key)) {
value = &old_table.data[pos];
check_old_table = false;
}
} else if (!is_deleted_flag) {
// we hit an empty field here, we don't
// need to further check this old table
// because we know it's not in here.
check_old_table = false;
}
}
if (check_new_table) {
int pos = (hash + i) % table.capacity;
int flags_pos = pos / 4;
int flags_pos_offset = pos % 4;
bool is_filled_flag = (table.flags[flags_pos] & (1 << (2 * flags_pos_offset))) > 0;
bool is_deleted_flag = (table.flags[flags_pos] & (1 << (2 * flags_pos_offset + 1))) > 0;
if (is_filled_flag) {
// found our entry?
if (table.hashes[pos] == hash && Comparator::compare(table.keys[pos], p_key)) {
if (r_data != NULL)
*r_data = table.data[pos];
return true;
}
continue;
} else if (is_deleted_flag) {
continue;
} else if (value != NULL) {
// We found a value in the old table
if (r_data != NULL)
*r_data = *value;
return true;
} else {
check_new_table = false;
}
}
}
if (value != NULL) {
if (r_data != NULL)
*r_data = *value;
if (exists) {
r_data.~TValue();
memnew_placement(&r_data, TValue(values[pos]));
return true;
}
return false;
}
_FORCE_INLINE_ bool has(const TKey &p_key) {
return lookup(p_key, NULL);
uint32_t _pos = 0;
return _lookup_pos(p_key, _pos);
}
void remove(const TKey &p_key) {
uint32_t hash = Hasher::hash(p_key);
uint32_t pos = 0;
bool exists = _lookup_pos(p_key, pos);
bool check_old_table = is_rehashing;
bool check_new_table = true;
for (int i = 0; i < table.capacity; i++) {
if (!check_new_table && !check_old_table) {
return;
}
// if we're rehashing check the old table
if (check_old_table && i < old_table.capacity) {
int pos = (hash + i) % old_table.capacity;
int flags_pos = pos / 4;
int flags_pos_offset = pos % 4;
bool is_filled_flag = (old_table.flags[flags_pos] & (1 << (2 * flags_pos_offset))) > 0;
bool is_deleted_flag = (old_table.flags[flags_pos] & (1 << (2 * flags_pos_offset + 1))) > 0;
if (is_filled_flag) {
// found our entry?
if (old_table.hashes[pos] == hash && Comparator::compare(old_table.keys[pos], p_key)) {
old_table.keys[pos].~TKey();
old_table.data[pos].~TData();
memnew_placement(&old_table.keys[pos], TKey);
memnew_placement(&old_table.data[pos], TData);
old_table.flags[flags_pos] &= ~(1 << (2 * flags_pos_offset));
old_table.flags[flags_pos] |= (1 << (2 * flags_pos_offset + 1));
elements--;
return;
}
} else if (!is_deleted_flag) {
// we hit an empty field here, we don't
// need to further check this old table
// because we know it's not in here.
check_old_table = false;
}
}
if (check_new_table) {
int pos = (hash + i) % table.capacity;
int flags_pos = pos / 4;
int flags_pos_offset = pos % 4;
bool is_filled_flag = (table.flags[flags_pos] & (1 << (2 * flags_pos_offset))) > 0;
bool is_deleted_flag = (table.flags[flags_pos] & (1 << (2 * flags_pos_offset + 1))) > 0;
if (is_filled_flag) {
// found our entry?
if (table.hashes[pos] == hash && Comparator::compare(table.keys[pos], p_key)) {
table.keys[pos].~TKey();
table.data[pos].~TData();
memnew_placement(&table.keys[pos], TKey);
memnew_placement(&table.data[pos], TData);
table.flags[flags_pos] &= ~(1 << (2 * flags_pos_offset));
table.flags[flags_pos] |= (1 << (2 * flags_pos_offset + 1));
// don't return here, this value might still be in the old table
// if it was already relocated.
elements--;
return;
}
continue;
} else if (is_deleted_flag) {
continue;
} else {
check_new_table = false;
}
}
if (!exists) {
return;
}
hashes[pos] |= DELETED_HASH_BIT;
values[pos].~TValue();
keys[pos].~TKey();
num_elements--;
}
struct Iterator {
bool valid;
uint32_t hash;
const TKey *key;
const TData *data;
const TValue *value;
private:
uint32_t pos;
friend class OAHashMap;
bool was_from_old_table;
};
Iterator iter() const {
Iterator it;
it.valid = false;
it.was_from_old_table = false;
it.valid = true;
it.pos = 0;
bool check_old_table = is_rehashing;
for (int i = 0; i < table.capacity; i++) {
// if we're rehashing check the old table first
if (check_old_table && i < old_table.capacity) {
int pos = i;
int flags_pos = pos / 4;
int flags_pos_offset = pos % 4;
bool is_filled_flag = (old_table.flags[flags_pos] & (1 << (2 * flags_pos_offset))) > 0;
if (is_filled_flag) {
it.valid = true;
it.hash = old_table.hashes[pos];
it.data = &old_table.data[pos];
it.key = &old_table.keys[pos];
it.was_from_old_table = true;
return it;
}
}
{
int pos = i;
int flags_pos = pos / 4;
int flags_pos_offset = pos % 4;
bool is_filled_flag = (table.flags[flags_pos] & (1 << (2 * flags_pos_offset))) > 0;
if (is_filled_flag) {
it.valid = true;
it.hash = table.hashes[pos];
it.data = &table.data[pos];
it.key = &table.keys[pos];
return it;
}
}
}
return it;
return next_iter(it);
}
Iterator next_iter(const Iterator &p_iter) const {
if (!p_iter.valid) {
return p_iter;
}
Iterator it;
it.valid = false;
it.was_from_old_table = false;
it.pos = p_iter.pos;
it.key = NULL;
it.value = NULL;
bool check_old_table = is_rehashing;
for (uint32_t i = it.pos; i < capacity; i++) {
it.pos = i + 1;
// we use this to skip the first check or not
bool was_from_old_table = p_iter.was_from_old_table;
int prev_index = (p_iter.data - (p_iter.was_from_old_table ? old_table.data : table.data));
if (!was_from_old_table) {
prev_index++;
}
for (int i = prev_index; i < table.capacity; i++) {
// if we're rehashing check the old table first
if (check_old_table && i < old_table.capacity && !was_from_old_table) {
int pos = i;
int flags_pos = pos / 4;
int flags_pos_offset = pos % 4;
bool is_filled_flag = (old_table.flags[flags_pos] & (1 << (2 * flags_pos_offset))) > 0;
if (is_filled_flag) {
it.valid = true;
it.hash = old_table.hashes[pos];
it.data = &old_table.data[pos];
it.key = &old_table.keys[pos];
it.was_from_old_table = true;
return it;
}
if (hashes[i] == EMPTY_HASH) {
continue;
}
if (hashes[i] & DELETED_HASH_BIT) {
continue;
}
was_from_old_table = false;
{
int pos = i;
int flags_pos = pos / 4;
int flags_pos_offset = pos % 4;
bool is_filled_flag = (table.flags[flags_pos] & (1 << (2 * flags_pos_offset))) > 0;
if (is_filled_flag) {
it.valid = true;
it.hash = table.hashes[pos];
it.data = &table.data[pos];
it.key = &table.keys[pos];
return it;
}
}
it.valid = true;
it.key = &keys[i];
it.value = &values[i];
return it;
}
return it;
}
OAHashMap(uint32_t p_initial_capacity = INITIAL_NUM_ELEMENTS) {
OAHashMap(uint32_t p_initial_capacity = 64) {
#ifdef OA_HASH_MAP_INITIAL_LOCAL_STORAGE
capacity = p_initial_capacity;
num_elements = 0;
if (p_initial_capacity <= INITIAL_NUM_ELEMENTS) {
table.data = local_data;
table.keys = local_keys;
table.hashes = local_hashes;
table.flags = local_flags;
keys = memnew_arr(TKey, p_initial_capacity);
values = memnew_arr(TValue, p_initial_capacity);
hashes = memnew_arr(uint32_t, p_initial_capacity);
zeromem(table.flags, INITIAL_NUM_ELEMENTS / 4 + (INITIAL_NUM_ELEMENTS % 4 != 0 ? 1 : 0));
table.capacity = INITIAL_NUM_ELEMENTS;
elements = 0;
} else
#endif
{
table.data = memnew_arr(TData, p_initial_capacity);
table.keys = memnew_arr(TKey, p_initial_capacity);
table.hashes = memnew_arr(uint32_t, p_initial_capacity);
table.flags = memnew_arr(uint8_t, p_initial_capacity / 4 + (p_initial_capacity % 4 != 0 ? 1 : 0));
zeromem(table.flags, p_initial_capacity / 4 + (p_initial_capacity % 4 != 0 ? 1 : 0));
table.capacity = p_initial_capacity;
elements = 0;
for (int i = 0; i < p_initial_capacity; i++) {
hashes[i] = 0;
}
is_rehashing = false;
rehash_position = 0;
}
~OAHashMap() {
#ifdef OA_HASH_MAP_INITIAL_LOCAL_STORAGE
if (table.capacity <= INITIAL_NUM_ELEMENTS) {
return; // Everything is local, so no cleanup :P
}
#endif
if (is_rehashing) {
#ifdef OA_HASH_MAP_INITIAL_LOCAL_STORAGE
if (old_table.data == local_data) {
// Everything is local, so no cleanup :P
} else
#endif
{
memdelete_arr(old_table.data);
memdelete_arr(old_table.keys);
memdelete_arr(old_table.hashes);
memdelete_arr(old_table.flags);
}
}
memdelete_arr(table.data);
memdelete_arr(table.keys);
memdelete_arr(table.hashes);
memdelete_arr(table.flags);
memdelete_arr(keys);
memdelete_arr(values);
memdelete(hashes);
}
};

6
main/tests/test_oa_hash_map.cpp
View file

@ -49,7 +49,7 @@ MainLoop *test() {
map.set(42, 11880);
int value;
map.lookup(42, &value);
map.lookup(42, value);
OS::get_singleton()->print("capacity %d\n", map.get_capacity());
OS::get_singleton()->print("elements %d\n", map.get_num_elements());
@ -72,7 +72,7 @@ MainLoop *test() {
uint32_t num_elems = 0;
for (int i = 0; i < 500; i++) {
int tmp;
if (map.lookup(i, &tmp))
if (map.lookup(i, tmp) && tmp == i * 2)
num_elems++;
}
@ -88,7 +88,7 @@ MainLoop *test() {
map.set("Godot rocks", 42);
for (OAHashMap<String, int>::Iterator it = map.iter(); it.valid; it = map.next_iter(it)) {
OS::get_singleton()->print("map[\"%s\"] = %d\n", it.key->utf8().get_data(), *it.data);
OS::get_singleton()->print("map[\"%s\"] = %d\n", it.key->utf8().get_data(), *it.value);
}
}

2
modules/csg/csg.cpp
View file

@ -1255,7 +1255,7 @@ void CSGBrushOperation::MeshMerge::add_face(const Vector3 &p_a, const Vector3 &p
vk.z = int((double(src_points[i].z) + double(vertex_snap) * 0.31234) / double(vertex_snap));
int res;
if (snap_cache.lookup(vk, &res)) {
if (snap_cache.lookup(vk, res)) {
indices[i] = res;
} else {
indices[i] = points.size();

2
modules/csg/csg.h
View file

@ -108,7 +108,7 @@ struct CSGBrushOperation {
}
};
OAHashMap<VertexKey, int, 64, VertexKeyHash> snap_cache;
OAHashMap<VertexKey, int, VertexKeyHash> snap_cache;
Vector<Vector3> points;

4
modules/csg/csg_shape.cpp
View file

@ -157,7 +157,7 @@ void CSGShape::_update_shape() {
for (int j = 0; j < 3; j++) {
Vector3 v = n->faces[i].vertices[j];
Vector3 add;
if (vec_map.lookup(v, &add)) {
if (vec_map.lookup(v, add)) {
add += p.normal;
} else {
add = p.normal;
@ -233,7 +233,7 @@ void CSGShape::_update_shape() {
Vector3 normal = p.normal;
if (n->faces[i].smooth && vec_map.lookup(v, &normal)) {
if (n->faces[i].smooth && vec_map.lookup(v, normal)) {
normal.normalize();
}