GCC Code Coverage Report

Directory: cvmfs/
File: cvmfs/smallhash.h
Date: 2026-02-22 02:35:58
Exec Total Coverage
Lines: 260 263 98.9%
Branches: 89 110 80.9%
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 #ifndef __STDC_FORMAT_MACROS
9 // NOLINTNEXTLINE
10 #define __STDC_FORMAT_MACROS
11 #endif
12
13 #include "duplex_testing.h"
14 #include <inttypes.h>
15 #include <pthread.h>
16 #include <stdint.h>
17
18 #include <algorithm>
19 #include <cassert>
20 #include <cstdlib>
21 #include <new>
22
23 #include "util/atomic.h"
24 #include "util/murmur.hxx"
25 #include "util/prng.h"
26 #include "util/smalloc.h"
27
28 /**
29 * Hash table with linear probing as collision resolution. Works only for
30 * a fixed (maximum) number of elements, i.e. no resizing. Load factor fixed
31 * to 0.7.
32 */
33 template<class Key, class Value, class Derived>
34 class SmallHashBase {
35 FRIEND_TEST(T_Smallhash, InsertAndCopyMd5Slow);
36
37 public:
38 static const double kLoadFactor; // mainly useless for the dynamic version
39 static const double kThresholdGrow; // only used for resizable version
40 static const double kThresholdShrink; // only used for resizable version
41
42 142265 SmallHashBase() {
43 142265 keys_ = NULL;
44 142265 values_ = NULL;
45 142265 hasher_ = NULL;
46 142265 bytes_allocated_ = 0;
47 142265 num_collisions_ = 0;
48 142265 max_collisions_ = 0;
49
50 // Properly initialized by Init()
51 142265 capacity_ = 0;
52 142265 initial_capacity_ = 0;
53 142265 size_ = 0;
54 142265 }
55
56 142127 ~SmallHashBase() { DeallocMemory(keys_, values_, capacity_); }
57
58 142217 void Init(uint32_t expected_size, Key empty,
59 uint32_t (*hasher)(const Key &key)) {
60 142217 hasher_ = hasher;
61 142217 empty_key_ = empty;
62 142217 capacity_ = static_cast<uint32_t>(static_cast<double>(expected_size)
63 142217 / kLoadFactor);
64 142217 initial_capacity_ = capacity_;
65 142217 static_cast<Derived *>(this)->SetThresholds(); // No-op for fixed size
66 142217 AllocMemory();
67 142217 this->DoClear(false);
68 142217 }
69
70 79440956 bool Lookup(const Key &key, Value *value) const {
71 uint32_t bucket;
72 uint32_t collisions;
73
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 79440956 const bool found = DoLookup(key, &bucket, &collisions);
74
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 79532189 if (found)
75
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 65965783 *value = values_[bucket];
76 79532189 return found;
77 }
78
79 /**
80 * Returns both the key and the value. That is useful if Key's equality
81 * operator implements an equivalence relation on Key. In this case, LookupEx
82 * returns the key representing the equivalence class that has been used
83 * during Insert().
84 * Used to return a glue::InodeEx element when looking for an inode.
85 */
86 92 bool LookupEx(Key *key, Value *value) const {
87 92 uint32_t bucket = ScaleHash(*key);
88
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 92 while (!(keys_[bucket] == empty_key_)) {
89
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 60 if (keys_[bucket] == *key) {
90 60 *key = keys_[bucket];
91 60 *value = values_[bucket];
92 60 return true;
93 }
94 ✗ bucket = (bucket + 1) % capacity_;
95 }
96 32 return false;
97 }
98
99 1015868 bool Contains(const Key &key) const {
100 uint32_t bucket;
101 uint32_t collisions;
102
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 1015868 const bool found = DoLookup(key, &bucket, &collisions);
103 1015868 return found;
104 }
105
106 1379818058 void Insert(const Key &key, const Value &value) {
107 1379818058 static_cast<Derived *>(this)->Grow(); // No-op if fixed-size
108 1374646907 const bool overwritten = DoInsert(key, value, true);
109 1373544221 size_ += !overwritten; // size + 1 if the key was not yet in the map
110 1373544221 }
111
112 82592233 bool Erase(const Key &key) {
113 uint32_t bucket;
114 uint32_t collisions;
115
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 82592233 const bool found = DoLookup(key, &bucket, &collisions);
116
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 80250655 if (found) {
117 80262559 keys_[bucket] = empty_key_;
118 80262559 size_--;
119 80262559 bucket = (bucket + 1) % capacity_;
120
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 221619683 while (!(keys_[bucket] == empty_key_)) {
121 142588876 Key rehash = keys_[bucket];
122 142588876 keys_[bucket] = empty_key_;
123
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 142588876 DoInsert(rehash, values_[bucket], false);
124 141357124 bucket = (bucket + 1) % capacity_;
125 }
126
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 79030807 static_cast<Derived *>(this)->Shrink(); // No-op if fixed-size
127 }
128 80434765 return found;
129 }
130
131 1110 void Clear() { DoClear(true); }
132
133 4295 uint64_t bytes_allocated() const { return bytes_allocated_; }
134 1182 static double GetEntrySize() {
135 2364 const double unit = sizeof(Key) + sizeof(Value);
136 2364 return unit / kLoadFactor;
137 }
138
139 void GetCollisionStats(uint64_t *num_collisions,
140 uint32_t *max_collisions) const {
141 *num_collisions = num_collisions_;
142 *max_collisions = max_collisions_;
143 }
144
145 // Careful with the direct access TODO: iterator
146 uint32_t capacity() const { return capacity_; }
147 12534 Key empty_key() const { return empty_key_; }
148 65106 Key *keys() const { return keys_; }
149 79 Value *values() const { return values_; }
150
151 // Only needed by compat
152 ✗ void SetHasher(uint32_t (*hasher)(const Key &key)) { hasher_ = hasher; }
153
154 protected:
155 1888815656 uint32_t ScaleHash(const Key &key) const {
156 1888815656 const double bucket = (static_cast<double>(hasher_(key))
157 1882617212 * static_cast<double>(capacity_)
158 / static_cast<double>(static_cast<uint32_t>(-1)));
159 1882617212 return static_cast<uint32_t>(bucket) % capacity_;
160 }
161
162 248471 void AllocMemory() {
163 248471 keys_ = static_cast<Key *>(smmap(capacity_ * sizeof(Key)));
164 248471 values_ = static_cast<Value *>(smmap(capacity_ * sizeof(Value)));
165
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 2119965934 for (uint32_t i = 0; i < capacity_; ++i) {
166 2119717463 /*keys_[i] =*/new (keys_ + i) Key();
167 }
168
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 2120586286 for (uint32_t i = 0; i < capacity_; ++i) {
169 2120310839 /*values_[i] =*/new (values_ + i) Value();
170 }
171 275447 bytes_allocated_ = (sizeof(Key) + sizeof(Value)) * capacity_;
172 275447 }
173
174 248381 void DeallocMemory(Key *k, Value *v, uint32_t c) {
175
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 2120701330 for (uint32_t i = 0; i < c; ++i) {
176 2120452949 k[i].~Key();
177 }
178
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 2115988402 for (uint32_t i = 0; i < c; ++i) {
179 2115740021 v[i].~Value();
180 }
181
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 248381 if (k)
182 248333 smunmap(k);
183
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 248381 if (v)
184 248333 smunmap(v);
185 248381 k = NULL;
186 248381 v = NULL;
187 248381 }
188
189 // Returns true iff the key is overwritten
190 1628459115 bool DoInsert(const Key &key, const Value &value,
191 const bool count_collisions) {
192 uint32_t bucket;
193 uint32_t collisions;
194
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 1628459115 const bool overwritten = DoLookup(key, &bucket, &collisions);
195
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 1626269697 if (count_collisions) {
196 1374537392 num_collisions_ += collisions;
197 1374537392 max_collisions_ = std::max(collisions, max_collisions_);
198 }
199 1625254077 keys_[bucket] = key;
200
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 1625254077 values_[bucket] = value;
201 1625254077 return overwritten;
202 }
203
204 1890165189 bool DoLookup(const Key &key, uint32_t *bucket, uint32_t *collisions) const {
205 1890165189 *bucket = ScaleHash(key);
206 1881934455 *collisions = 0;
207
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 19228085000 while (!(keys_[*bucket] == empty_key_)) {
208
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 17621825119 if (keys_[*bucket] == key)
209 275674574 return true;
210 17346150545 *bucket = (*bucket + 1) % capacity_;
211 17346150545 (*collisions)++;
212 }
213 1606259881 return false;
214 }
215
216 248531 void DoClear(const bool reset_capacity) {
217
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 248531 if (reset_capacity)
218 2143 static_cast<Derived *>(this)->ResetCapacity(); // No-op if fixed-size
219
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 2122254646 for (uint32_t i = 0; i < capacity_; ++i)
220 2122006115 keys_[i] = empty_key_;
221 248531 size_ = 0;
222 248531 }
223
224 // Methods for resizable version
225 void SetThresholds() { }
226 void Grow() { }
227 void Shrink() { }
228 void ResetCapacity() { }
229
230 // Separate key and value arrays for better locality
231 Key *keys_;
232 Value *values_;
233 uint32_t capacity_;
234 uint32_t initial_capacity_;
235 uint32_t size_;
236 uint32_t (*hasher_)(const Key &key);
237 uint64_t bytes_allocated_;
238 uint64_t num_collisions_;
239 uint32_t max_collisions_; /**< maximum collisions for a single insert */
240 Key empty_key_;
241 };
242
243
244 template<class Key, class Value>
245 class SmallHashFixed
246 : public SmallHashBase<Key, Value, SmallHashFixed<Key, Value> > {
247 friend class SmallHashBase<Key, Value, SmallHashFixed<Key, Value> >;
248
249 protected:
250 // No-ops
251 4235 void SetThresholds() { }
252 342783 void Grow() { }
253 30126 void Shrink() { }
254 60 void ResetCapacity() { }
255 };
256
257
258 template<class Key, class Value>
259 class SmallHashDynamic
260 : public SmallHashBase<Key, Value, SmallHashDynamic<Key, Value> > {
261 friend class SmallHashBase<Key, Value, SmallHashDynamic<Key, Value> >;
262
263 public:
264 typedef SmallHashBase<Key, Value, SmallHashDynamic<Key, Value> > Base;
265 static const double kThresholdGrow;
266 static const double kThresholdShrink;
267
268 138030 SmallHashDynamic() : Base() {
269 138030 num_migrates_ = 0;
270
271 // Properly set by Init
272 138030 threshold_grow_ = 0;
273 138030 threshold_shrink_ = 0;
274 138030 }
275
276 SmallHashDynamic(const SmallHashDynamic<Key, Value> &other) : Base() {
277 num_migrates_ = 0;
278 CopyFrom(other);
279 }
280
281 168 SmallHashDynamic<Key, Value> &operator=(
282 const SmallHashDynamic<Key, Value> &other) {
283
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 168 if (&other == this)
284 ✗ return *this;
285
286 168 CopyFrom(other);
287 168 return *this;
288 }
289
290 34499429 uint32_t capacity() const { return Base::capacity_; }
291 784318107 uint32_t size() const { return Base::size_; }
292 uint32_t num_migrates() const { return num_migrates_; }
293
294 protected:
295 244236 void SetThresholds() {
296 244236 threshold_grow_ = static_cast<uint32_t>(static_cast<double>(capacity())
297 244236 * kThresholdGrow);
298 244236 threshold_shrink_ = static_cast<uint32_t>(static_cast<double>(capacity())
299 244236 * kThresholdShrink);
300 244236 }
301
302 1377973764 void Grow() {
303
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 1377973764 if (size() > threshold_grow_)
304 71140 Migrate(capacity() * 2);
305 1375434804 }
306
307 80096710 void Shrink() {
308
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 80096710 if (size() < threshold_shrink_) {
309 16885414 const uint32_t target_capacity = capacity() / 2;
310
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 16880581 if (target_capacity >= Base::initial_capacity_)
311 16512 Migrate(target_capacity);
312 }
313 80232394 }
314
315 2083 void ResetCapacity() {
316 2083 Base::DeallocMemory(Base::keys_, Base::values_, Base::capacity_);
317 2083 Base::capacity_ = Base::initial_capacity_;
318 2083 Base::AllocMemory();
319 2083 SetThresholds();
320 2083 }
321
322 private:
323 // Returns a random permutation of indices [0..N-1] that is allocated
324 // by smmap (Knuth's shuffle algorithm)
325 33216 uint32_t *ShuffleIndices(const uint32_t N) {
326 33216 uint32_t *shuffled = static_cast<uint32_t *>(smmap(N * sizeof(uint32_t)));
327 // Init with identity
328
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 538982016 for (unsigned i = 0; i < N; ++i)
329 538948800 shuffled[i] = i;
330 // Shuffle (no shuffling for the last element)
331
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 512939424 for (unsigned i = 0; i < N - 1; ++i) {
332 512961264 const uint32_t swap_idx = i + g_prng.Next(N - i);
333 512906208 const uint32_t tmp = shuffled[i];
334 512906208 shuffled[i] = shuffled[swap_idx];
335 512906208 shuffled[swap_idx] = tmp;
336 }
337 168 return shuffled;
338 }
339
340 104164 void Migrate(const uint32_t new_capacity) {
341 104164 Key *old_keys = Base::keys_;
342 104164 Value *old_values = Base::values_;
343 104164 const uint32_t old_capacity = capacity();
344 104164 const uint32_t old_size = size();
345
346 104164 Base::capacity_ = new_capacity;
347 104164 SetThresholds();
348 104164 Base::AllocMemory();
349 104164 Base::DoClear(false);
350
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 104164 if (new_capacity < old_capacity) {
351 33024 uint32_t *shuffled_indices = ShuffleIndices(old_capacity);
352
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 464358528 for (uint32_t i = 0; i < old_capacity; ++i) {
353
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 464355168 if (old_keys[shuffled_indices[i]] != Base::empty_key_) {
354 116485392 Base::Insert(old_keys[shuffled_indices[i]],
355 116485392 old_values[shuffled_indices[i]]);
356 }
357 }
358 3360 smunmap(shuffled_indices);
359 } else {
360
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 880587946 for (uint32_t i = 0; i < old_capacity; ++i) {
361
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 880537590 if (old_keys[i] != Base::empty_key_)
362 660732322 Base::Insert(old_keys[i], old_values[i]);
363 }
364 }
365
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 83380 assert(size() == old_size);
366
367 104164 Base::DeallocMemory(old_keys, old_values, old_capacity);
368 104164 num_migrates_++;
369 104164 }
370
371 168 void CopyFrom(const SmallHashDynamic<Key, Value> &other) {
372 168 uint32_t *shuffled_indices = ShuffleIndices(other.capacity_);
373
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 33033336 for (uint32_t i = 0; i < other.capacity_; ++i) {
374
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 33033168 if (other.keys_[shuffled_indices[i]] != other.empty_key_) {
375 24000000 this->Insert(other.keys_[shuffled_indices[i]],
376 24000000 other.values_[shuffled_indices[i]]);
377 }
378 }
379 168 smunmap(shuffled_indices);
380 168 }
381
382 uint32_t num_migrates_;
383 uint32_t threshold_grow_;
384 uint32_t threshold_shrink_;
385 static Prng g_prng;
386 };
387
388
389 /**
390 * Distributes the key-value pairs over $n$ dynamic hash maps with individual
391 * mutexes. Hence low mutex contention, and benefits from multiple processors.
392 */
393 template<class Key, class Value>
394 class MultiHash {
395 public:
396 240 MultiHash() {
397 240 num_hashmaps_ = 0;
398 240 hashmaps_ = NULL;
399 240 locks_ = NULL;
400 240 }
401
402 240 void Init(const uint8_t num_hashmaps, const Key &empty_key,
403 uint32_t (*hasher)(const Key &key)) {
404
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 240 assert(num_hashmaps > 0);
405 240 const uint8_t N = num_hashmaps;
406 240 num_hashmaps_ = N;
407
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 10320 hashmaps_ = new SmallHashDynamic<Key, Value>[N]();
408 240 locks_ = static_cast<pthread_mutex_t *>(
409 240 smalloc(N * sizeof(pthread_mutex_t)));
410
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 10320 for (uint8_t i = 0; i < N; ++i) {
411 10080 int retval = pthread_mutex_init(&locks_[i], NULL);
412
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 10080 assert(retval == 0);
413 10080 hashmaps_[i].Init(128, empty_key, hasher);
414 }
415 240 }
416
417 240 ~MultiHash() {
418
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 10320 for (uint8_t i = 0; i < num_hashmaps_; ++i) {
419 10080 pthread_mutex_destroy(&locks_[i]);
420 }
421 240 free(locks_);
422
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 10320 delete[] hashmaps_;
423 240 }
424
425 24000000 bool Lookup(const Key &key, Value *value) {
426 24000000 uint8_t target = SelectHashmap(key);
427 24000000 Lock(target);
428 24000000 const bool result = hashmaps_[target].Lookup(key, value);
429 24000000 Unlock(target);
430 24000000 return result;
431 }
432
433 89982120 void Insert(const Key &key, const Value &value) {
434 89982120 uint8_t target = SelectHashmap(key);
435 87353904 Lock(target);
436 90626664 hashmaps_[target].Insert(key, value);
437 85915296 Unlock(target);
438 93428400 }
439
440 42958296 void Erase(const Key &key) {
441 42958296 uint8_t target = SelectHashmap(key);
442 41120352 Lock(target);
443 43988208 hashmaps_[target].Erase(key);
444 39644280 Unlock(target);
445 44657040 }
446
447 24 void Clear() {
448
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 1032 for (uint8_t i = 0; i < num_hashmaps_; ++i)
449 1008 Lock(i);
450
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 1032 for (uint8_t i = 0; i < num_hashmaps_; ++i)
451 1008 hashmaps_[i].Clear();
452
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 1032 for (uint8_t i = 0; i < num_hashmaps_; ++i)
453 1008 Unlock(i);
454 24 }
455
456 240 uint8_t num_hashmaps() const { return num_hashmaps_; }
457
458 192 void GetSizes(uint32_t *sizes) {
459
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 8256 for (uint8_t i = 0; i < num_hashmaps_; ++i) {
460 8064 Lock(i);
461 8064 sizes[i] = hashmaps_[i].size();
462 8064 Unlock(i);
463 }
464 192 }
465
466 void GetCollisionStats(uint64_t *num_collisions, uint32_t *max_collisions) {
467 for (uint8_t i = 0; i < num_hashmaps_; ++i) {
468 Lock(i);
469 hashmaps_[i].GetCollisionStats(&num_collisions[i], &max_collisions[i]);
470 Unlock(i);
471 }
472 }
473
474 private:
475 155725848 inline uint8_t SelectHashmap(const Key &key) {
476 155725848 uint32_t hash = MurmurHash2(&key, sizeof(key), 0x37);
477 153242400 double bucket = static_cast<double>(hash)
478 153242400 * static_cast<double>(num_hashmaps_)
479 / static_cast<double>(static_cast<uint32_t>(-1));
480 153242400 return static_cast<uint32_t>(bucket) % num_hashmaps_;
481 }
482
483 151953288 inline void Lock(const uint8_t target) {
484 151953288 int retval = pthread_mutex_lock(&locks_[target]);
485
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 164285640 assert(retval == 0);
486 164285640 }
487
488 149831472 inline void Unlock(const uint8_t target) {
489 149831472 int retval = pthread_mutex_unlock(&locks_[target]);
490
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 165380520 assert(retval == 0);
491 165380520 }
492
493 uint8_t num_hashmaps_;
494 SmallHashDynamic<Key, Value> *hashmaps_;
495 pthread_mutex_t *locks_;
496 };
497
498
499 // initialize the static fields
500 template<class Key, class Value>
501 Prng SmallHashDynamic<Key, Value>::g_prng;
502
503 template<class Key, class Value, class Derived>
504 const double SmallHashBase<Key, Value, Derived>::kLoadFactor = 0.75;
505
506 template<class Key, class Value>
507 const double SmallHashDynamic<Key, Value>::kThresholdGrow = 0.75;
508
509 template<class Key, class Value>
510 const double SmallHashDynamic<Key, Value>::kThresholdShrink = 0.25;
511
512 #endif // CVMFS_SMALLHASH_H_
513