GCC Code Coverage Report

Directory: cvmfs/
File: cvmfs/smallhash.h
Date: 2026-10-11 02:40:02
Exec Total Coverage
Lines: 259 263 98.5%
Branches: 88 110 80.0%
Line Branch Exec Source
1 /**
2 * This file is part of the CernVM File System.
3 */
4
5 #ifndef CVMFS_SMALLHASH_H_
6 #define CVMFS_SMALLHASH_H_
7
8 #include <inttypes.h>
9 #include <pthread.h>
10 #include <stdint.h>
11
12 #include <algorithm>
13 #include <atomic>
14 #include <cassert>
15 #include <cstdlib>
16 #include <new>
17
18 #include "duplex_testing.h"
19 #include "util/murmur.hxx"
20 #include "util/prng.h"
21 #include "util/smalloc.h"
22
23 /**
24 * Hash table with linear probing as collision resolution. Works only for
25 * a fixed (maximum) number of elements, i.e. no resizing. Load factor fixed
26 * to 0.7.
27 */
28 template<class Key, class Value, class Derived>
29 class SmallHashBase {
30 FRIEND_TEST(T_Smallhash, InsertAndCopyMd5Slow);
31
32 public:
33 static const double kLoadFactor; // mainly useless for the dynamic version
34 static const double kThresholdGrow; // only used for resizable version
35 static const double kThresholdShrink; // only used for resizable version
36
37 142387 SmallHashBase() {
38 142387 keys_ = NULL;
39 142387 values_ = NULL;
40 142387 hasher_ = NULL;
41 142387 bytes_allocated_ = 0;
42 142387 num_collisions_ = 0;
43 142387 max_collisions_ = 0;
44
45 // Properly initialized by Init()
46 142387 capacity_ = 0;
47 142387 initial_capacity_ = 0;
48 142387 size_ = 0;
49 142387 }
50
51 142249 ~SmallHashBase() { DeallocMemory(keys_, values_, capacity_); }
52
53 142371 void Init(uint32_t expected_size, Key empty,
54 uint32_t (*hasher)(const Key &key)) {
55 142371 hasher_ = hasher;
56 142371 empty_key_ = empty;
57 142371 capacity_ = static_cast<uint32_t>(static_cast<double>(expected_size)
58 142371 / kLoadFactor);
59 142371 initial_capacity_ = capacity_;
60 142371 static_cast<Derived *>(this)->SetThresholds(); // No-op for fixed size
61 142371 AllocMemory();
62 142371 this->DoClear(false);
63 142371 }
64
65 38896002 bool Lookup(const Key &key, Value *value) const {
66 uint32_t bucket;
67 uint32_t collisions;
68
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 38896002 const bool found = DoLookup(key, &bucket, &collisions);
69
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 38908656 if (found)
70
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 29854452 *value = values_[bucket];
71 38908656 return found;
72 }
73
74 /**
75 * Returns both the key and the value. That is useful if Key's equality
76 * operator implements an equivalence relation on Key. In this case, LookupEx
77 * returns the key representing the equivalence class that has been used
78 * during Insert().
79 * Used to return a glue::InodeEx element when looking for an inode.
80 */
81 48 bool LookupEx(Key *key, Value *value) const {
82 48 uint32_t bucket = ScaleHash(*key);
83
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 48 while (!(keys_[bucket] == empty_key_)) {
84
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 32 if (keys_[bucket] == *key) {
85 32 *key = keys_[bucket];
86 32 *value = values_[bucket];
87 32 return true;
88 }
89 ✗ bucket = (bucket + 1) % capacity_;
90 }
91 16 return false;
92 }
93
94 19024065 bool Contains(const Key &key) const {
95 uint32_t bucket;
96 uint32_t collisions;
97
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 19024065 const bool found = DoLookup(key, &bucket, &collisions);
98 19024065 return found;
99 }
100
101 609519112 void Insert(const Key &key, const Value &value) {
102 609519112 static_cast<Derived *>(this)->Grow(); // No-op if fixed-size
103 608234020 const bool overwritten = DoInsert(key, value, true);
104 607368498 size_ += !overwritten; // size + 1 if the key was not yet in the map
105 607368498 }
106
107 47217298 bool Erase(const Key &key) {
108 uint32_t bucket;
109 uint32_t collisions;
110
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 47217298 const bool found = DoLookup(key, &bucket, &collisions);
111
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 46299444 if (found) {
112 46300498 keys_[bucket] = empty_key_;
113 46300498 size_--;
114 46300498 bucket = (bucket + 1) % capacity_;
115
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 87446876 while (!(keys_[bucket] == empty_key_)) {
116 41446986 Key rehash = keys_[bucket];
117 41446986 keys_[bucket] = empty_key_;
118
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 41446986 DoInsert(rehash, values_[bucket], false);
119 41146378 bucket = (bucket + 1) % capacity_;
120 }
121
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 45999890 static_cast<Derived *>(this)->Shrink(); // No-op if fixed-size
122 }
123 46427416 return found;
124 }
125
126 483 void Clear() { DoClear(true); }
127
128 5913 uint64_t bytes_allocated() const { return bytes_allocated_; }
129 1614 static double GetEntrySize() {
130 3228 const double unit = sizeof(Key) + sizeof(Value);
131 3228 return unit / kLoadFactor;
132 }
133
134 void GetCollisionStats(uint64_t *num_collisions,
135 uint32_t *max_collisions) const {
136 *num_collisions = num_collisions_;
137 *max_collisions = max_collisions_;
138 }
139
140 // Careful with the direct access TODO: iterator
141 uint32_t capacity() const { return capacity_; }
142 6254 Key empty_key() const { return empty_key_; }
143 73018 Key *keys() const { return keys_; }
144 39 Value *values() const { return values_; }
145
146 // Only needed by compat
147 ✗ void SetHasher(uint32_t (*hasher)(const Key &key)) { hasher_ = hasher; }
148
149 protected:
150 860167480 uint32_t ScaleHash(const Key &key) const {
151 860167480 const double bucket = (static_cast<double>(hasher_(key))
152 857941116 * static_cast<double>(capacity_)
153 / static_cast<double>(static_cast<uint32_t>(-1)));
154 857941116 return static_cast<uint32_t>(bucket) % capacity_;
155 }
156
157 179273 void AllocMemory() {
158 179273 keys_ = static_cast<Key *>(smmap(capacity_ * sizeof(Key)));
159 179273 values_ = static_cast<Value *>(smmap(capacity_ * sizeof(Value)));
160
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 1351920758 for (uint32_t i = 0; i < capacity_; ++i) {
161 1351741485 /*keys_[i] =*/new (keys_ + i) Key();
162 }
163
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 1353787350 for (uint32_t i = 0; i < capacity_; ++i) {
164 1353601933 /*values_[i] =*/new (values_ + i) Value();
165 }
166 185417 bytes_allocated_ = (sizeof(Key) + sizeof(Value)) * capacity_;
167 185417 }
168
169 179151 void DeallocMemory(Key *k, Value *v, uint32_t c) {
170
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 1357843626 for (uint32_t i = 0; i < c; ++i) {
171 1357664475 k[i].~Key();
172 }
173
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 1359851386 for (uint32_t i = 0; i < c; ++i) {
174 1359672235 v[i].~Value();
175 }
176
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 179151 if (k)
177 179135 smunmap(k);
178
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 179151 if (v)
179 179135 smunmap(v);
180 179151 k = NULL;
181 179151 v = NULL;
182 179151 }
183
184 // Returns true iff the key is overwritten
185 689081858 bool DoInsert(const Key &key, const Value &value,
186 const bool count_collisions) {
187 uint32_t bucket;
188 uint32_t collisions;
189
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 689081858 const bool overwritten = DoLookup(key, &bucket, &collisions);
190
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 688093068 if (count_collisions) {
191 607380850 num_collisions_ += collisions;
192 607380850 max_collisions_ = std::max(collisions, max_collisions_);
193 }
194 687912964 keys_[bucket] = key;
195
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 687912964 values_[bucket] = value;
196 687912964 return overwritten;
197 }
198
199 860785048 bool DoLookup(const Key &key, uint32_t *bucket, uint32_t *collisions) const {
200 860785048 *bucket = ScaleHash(key);
201 857618734 *collisions = 0;
202
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 2162781714 while (!(keys_[*bucket] == empty_key_)) {
203
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 1482023927 if (keys_[*bucket] == key)
204 176860947 return true;
205 1305162980 *bucket = (*bucket + 1) % capacity_;
206 1305162980 (*collisions)++;
207 }
208 680757787 return false;
209 }
210
211 179275 void DoClear(const bool reset_capacity) {
212
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 179275 if (reset_capacity)
213 828 static_cast<Derived *>(this)->ResetCapacity(); // No-op if fixed-size
214
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 1357153042 for (uint32_t i = 0; i < capacity_; ++i)
215 1356973767 keys_[i] = empty_key_;
216 179275 size_ = 0;
217 179275 }
218
219 // Methods for resizable version
220 void SetThresholds() { }
221 void Grow() { }
222 void Shrink() { }
223 void ResetCapacity() { }
224
225 // Separate key and value arrays for better locality
226 Key *keys_;
227 Value *values_;
228 uint32_t capacity_;
229 uint32_t initial_capacity_;
230 uint32_t size_;
231 uint32_t (*hasher_)(const Key &key);
232 uint64_t bytes_allocated_;
233 uint64_t num_collisions_;
234 uint32_t max_collisions_; /**< maximum collisions for a single insert */
235 Key empty_key_;
236 };
237
238
239 template<class Key, class Value>
240 class SmallHashFixed
241 : public SmallHashBase<Key, Value, SmallHashFixed<Key, Value> > {
242 friend class SmallHashBase<Key, Value, SmallHashFixed<Key, Value> >;
243
244 protected:
245 // No-ops
246 5911 void SetThresholds() { }
247 982196 void Grow() { }
248 5782 void Shrink() { }
249 2 void ResetCapacity() { }
250 };
251
252
253 template<class Key, class Value>
254 class SmallHashDynamic
255 : public SmallHashBase<Key, Value, SmallHashDynamic<Key, Value> > {
256 friend class SmallHashBase<Key, Value, SmallHashDynamic<Key, Value> >;
257
258 public:
259 typedef SmallHashBase<Key, Value, SmallHashDynamic<Key, Value> > Base;
260 static const double kThresholdGrow;
261 static const double kThresholdShrink;
262
263 136476 SmallHashDynamic() : Base() {
264 136476 num_migrates_ = 0;
265
266 // Properly set by Init
267 136476 threshold_grow_ = 0;
268 136476 threshold_shrink_ = 0;
269 136476 }
270
271 SmallHashDynamic(const SmallHashDynamic<Key, Value> &other) : Base() {
272 num_migrates_ = 0;
273 CopyFrom(other);
274 }
275
276 376 SmallHashDynamic<Key, Value> &operator=(
277 const SmallHashDynamic<Key, Value> &other) {
278
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 376 if (&other == this)
279 ✗ return *this;
280
281 376 CopyFrom(other);
282 376 return *this;
283 }
284
285 48878786 uint32_t capacity() const { return Base::capacity_; }
286 375091822 uint32_t size() const { return Base::size_; }
287 uint32_t num_migrates() const { return num_migrates_; }
288
289 protected:
290 173362 void SetThresholds() {
291 173362 threshold_grow_ = static_cast<uint32_t>(static_cast<double>(capacity())
292 173362 * kThresholdGrow);
293 173362 threshold_shrink_ = static_cast<uint32_t>(static_cast<double>(capacity())
294 173346 * kThresholdShrink);
295 173346 }
296
297 607889163 void Grow() {
298
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 607889163 if (size() > threshold_grow_)
299 25048 Migrate(capacity() * 2);
300 607344287 }
301
302 46359166 void Shrink() {
303
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 46359166 if (size() < threshold_shrink_) {
304 24200162 const uint32_t target_capacity = capacity() / 2;
305
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 24198454 if (target_capacity >= Base::initial_capacity_)
306 5504 Migrate(target_capacity);
307 }
308 46408972 }
309
310 826 void ResetCapacity() {
311 826 Base::DeallocMemory(Base::keys_, Base::values_, Base::capacity_);
312 826 Base::capacity_ = Base::initial_capacity_;
313 826 Base::AllocMemory();
314 826 SetThresholds();
315 826 }
316
317 private:
318 // Returns a random permutation of indices [0..N-1] that is allocated
319 // by smmap (Knuth's shuffle algorithm)
320 11392 uint32_t *ShuffleIndices(const uint32_t N) {
321 11392 uint32_t *shuffled = static_cast<uint32_t *>(smmap(N * sizeof(uint32_t)));
322 // Init with identity
323
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 179207472 for (unsigned i = 0; i < N; ++i)
324 179196080 shuffled[i] = i;
325 // Shuffle (no shuffling for the last element)
326
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 169767088 for (unsigned i = 0; i < N - 1; ++i) {
327 169900992 const uint32_t swap_idx = i + g_prng.Next(N - i);
328 169755696 const uint32_t tmp = shuffled[i];
329 169755696 shuffled[i] = shuffled[swap_idx];
330 169755696 shuffled[swap_idx] = tmp;
331 }
332 376 return shuffled;
333 }
334
335 36056 void Migrate(const uint32_t new_capacity) {
336 36056 Key *old_keys = Base::keys_;
337 36056 Value *old_values = Base::values_;
338 36056 const uint32_t old_capacity = capacity();
339 36040 const uint32_t old_size = size();
340
341 36056 Base::capacity_ = new_capacity;
342 36056 SetThresholds();
343 36056 Base::AllocMemory();
344 36072 Base::DoClear(false);
345
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 36056 if (new_capacity < old_capacity) {
346 11008 uint32_t *shuffled_indices = ShuffleIndices(old_capacity);
347
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 154888480 for (uint32_t i = 0; i < old_capacity; ++i) {
348
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 155410448 if (old_keys[shuffled_indices[i]] != Base::empty_key_) {
349 38993008 Base::Insert(old_keys[shuffled_indices[i]],
350 38993008 old_values[shuffled_indices[i]]);
351 }
352 }
353 ✗ smunmap(shuffled_indices);
354 } else {
355
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 350160488 for (uint32_t i = 0; i < old_capacity; ++i) {
356
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 350146976 if (old_keys[i] != Base::empty_key_)
357 262710712 Base::Insert(old_keys[i], old_values[i]);
358 }
359 }
360
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 24520 assert(size() == old_size);
361
362 36072 Base::DeallocMemory(old_keys, old_values, old_capacity);
363 36072 num_migrates_++;
364 36072 }
365
366 376 void CopyFrom(const SmallHashDynamic<Key, Value> &other) {
367 376 uint32_t *shuffled_indices = ShuffleIndices(other.capacity_);
368
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 11018152 for (uint32_t i = 0; i < other.capacity_; ++i) {
369
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 11017776 if (other.keys_[shuffled_indices[i]] != other.empty_key_) {
370 8000000 this->Insert(other.keys_[shuffled_indices[i]],
371 8000000 other.values_[shuffled_indices[i]]);
372 }
373 }
374 376 smunmap(shuffled_indices);
375 376 }
376
377 uint32_t num_migrates_;
378 uint32_t threshold_grow_;
379 uint32_t threshold_shrink_;
380 static Prng g_prng;
381 };
382
383
384 /**
385 * Distributes the key-value pairs over $n$ dynamic hash maps with individual
386 * mutexes. Hence low mutex contention, and benefits from multiple processors.
387 */
388 template<class Key, class Value>
389 class MultiHash {
390 public:
391 80 MultiHash() {
392 80 num_hashmaps_ = 0;
393 80 hashmaps_ = NULL;
394 80 locks_ = NULL;
395 80 }
396
397 80 void Init(const uint8_t num_hashmaps, const Key &empty_key,
398 uint32_t (*hasher)(const Key &key)) {
399
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 80 assert(num_hashmaps > 0);
400 80 const uint8_t N = num_hashmaps;
401 80 num_hashmaps_ = N;
402
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 3440 hashmaps_ = new SmallHashDynamic<Key, Value>[N]();
403 80 locks_ = static_cast<pthread_mutex_t *>(
404 80 smalloc(N * sizeof(pthread_mutex_t)));
405
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 3440 for (uint8_t i = 0; i < N; ++i) {
406 3360 int retval = pthread_mutex_init(&locks_[i], NULL);
407
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 3360 assert(retval == 0);
408 3360 hashmaps_[i].Init(128, empty_key, hasher);
409 }
410 80 }
411
412 80 ~MultiHash() {
413
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 3440 for (uint8_t i = 0; i < num_hashmaps_; ++i) {
414 3360 pthread_mutex_destroy(&locks_[i]);
415 }
416 80 free(locks_);
417
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 3440 delete[] hashmaps_;
418 80 }
419
420 8000000 bool Lookup(const Key &key, Value *value) {
421 8000000 uint8_t target = SelectHashmap(key);
422 8000000 Lock(target);
423 8000000 const bool result = hashmaps_[target].Lookup(key, value);
424 8000000 Unlock(target);
425 8000000 return result;
426 }
427
428 29931200 void Insert(const Key &key, const Value &value) {
429 29931200 uint8_t target = SelectHashmap(key);
430 28917216 Lock(target);
431 30022592 hashmaps_[target].Insert(key, value);
432 28478608 Unlock(target);
433 30525896 }
434
435 14431632 void Erase(const Key &key) {
436 14431632 uint8_t target = SelectHashmap(key);
437 13722120 Lock(target);
438 14608704 hashmaps_[target].Erase(key);
439 13238840 Unlock(target);
440 14910272 }
441
442 8 void Clear() {
443
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 344 for (uint8_t i = 0; i < num_hashmaps_; ++i)
444 336 Lock(i);
445
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 344 for (uint8_t i = 0; i < num_hashmaps_; ++i)
446 336 hashmaps_[i].Clear();
447
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 344 for (uint8_t i = 0; i < num_hashmaps_; ++i)
448 336 Unlock(i);
449 8 }
450
451 80 uint8_t num_hashmaps() const { return num_hashmaps_; }
452
453 64 void GetSizes(uint32_t *sizes) {
454
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 2752 for (uint8_t i = 0; i < num_hashmaps_; ++i) {
455 2688 Lock(i);
456 2688 sizes[i] = hashmaps_[i].size();
457 2688 Unlock(i);
458 }
459 64 }
460
461 void GetCollisionStats(uint64_t *num_collisions, uint32_t *max_collisions) {
462 for (uint8_t i = 0; i < num_hashmaps_; ++i) {
463 Lock(i);
464 hashmaps_[i].GetCollisionStats(&num_collisions[i], &max_collisions[i]);
465 Unlock(i);
466 }
467 }
468
469 private:
470 52060032 inline uint8_t SelectHashmap(const Key &key) {
471 52060032 uint32_t hash = MurmurHash2(&key, sizeof(key), 0x37);
472 51012208 double bucket = static_cast<double>(hash)
473 51012208 * static_cast<double>(num_hashmaps_)
474 / static_cast<double>(static_cast<uint32_t>(-1));
475 51012208 return static_cast<uint32_t>(bucket) % num_hashmaps_;
476 }
477
478 50506216 inline void Lock(const uint8_t target) {
479 50506216 int retval = pthread_mutex_lock(&locks_[target]);
480
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 54812272 assert(retval == 0);
481 54812272 }
482
483 49765464 inline void Unlock(const uint8_t target) {
484 49765464 int retval = pthread_mutex_unlock(&locks_[target]);
485
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 55166488 assert(retval == 0);
486 55166488 }
487
488 uint8_t num_hashmaps_;
489 SmallHashDynamic<Key, Value> *hashmaps_;
490 pthread_mutex_t *locks_;
491 };
492
493
494 // initialize the static fields
495 template<class Key, class Value>
496 Prng SmallHashDynamic<Key, Value>::g_prng;
497
498 template<class Key, class Value, class Derived>
499 const double SmallHashBase<Key, Value, Derived>::kLoadFactor = 0.75;
500
501 template<class Key, class Value>
502 const double SmallHashDynamic<Key, Value>::kThresholdGrow = 0.75;
503
504 template<class Key, class Value>
505 const double SmallHashDynamic<Key, Value>::kThresholdShrink = 0.25;
506
507 #endif // CVMFS_SMALLHASH_H_
508