GCC Code Coverage Report

Directory: cvmfs/
File: cvmfs/smallhash.h
Date: 2026-10-04 02:40:33
Exec Total Coverage
Lines: 259 263 98.5%
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 #include "duplex_testing.h"
9 #include <inttypes.h>
10 #include <pthread.h>
11 #include <stdint.h>
12
13 #include <algorithm>
14 #include <cassert>
15 #include <cstdlib>
16 #include <new>
17
18 #include "util/atomic.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 112162 SmallHashBase() {
38 112162 keys_ = NULL;
39 112162 values_ = NULL;
40 112162 hasher_ = NULL;
41 112162 bytes_allocated_ = 0;
42 112162 num_collisions_ = 0;
43 112162 max_collisions_ = 0;
44
45 // Properly initialized by Init()
46 112162 capacity_ = 0;
47 112162 initial_capacity_ = 0;
48 112162 size_ = 0;
49 112162 }
50
51 112024 ~SmallHashBase() { DeallocMemory(keys_, values_, capacity_); }
52
53 112140 void Init(uint32_t expected_size, Key empty,
54 uint32_t (*hasher)(const Key &key)) {
55 112140 hasher_ = hasher;
56 112140 empty_key_ = empty;
57 112140 capacity_ = static_cast<uint32_t>(static_cast<double>(expected_size)
58 112140 / kLoadFactor);
59 112140 initial_capacity_ = capacity_;
60 112140 static_cast<Derived *>(this)->SetThresholds(); // No-op for fixed size
61 112140 AllocMemory();
62 112140 this->DoClear(false);
63 112140 }
64
65 36109776 bool Lookup(const Key &key, Value *value) const {
66 uint32_t bucket;
67 uint32_t collisions;
68
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 36109776 const bool found = DoLookup(key, &bucket, &collisions);
69
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 36119436 if (found)
70
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 29958690 *value = values_[bucket];
71 36119436 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 */
81 216 bool LookupEx(Key *key, Value *value) const {
82 216 uint32_t bucket = ScaleHash(*key);
83
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 216 while (!(keys_[bucket] == empty_key_)) {
84
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 144 if (keys_[bucket] == *key) {
85 144 *key = keys_[bucket];
86 144 *value = values_[bucket];
87 144 return true;
88 }
89 ✗ bucket = (bucket + 1) % capacity_;
90 }
91 72 return false;
92 }
93
94 35035591 bool Contains(const Key &key) const {
95 uint32_t bucket;
96 uint32_t collisions;
97
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 35035591 const bool found = DoLookup(key, &bucket, &collisions);
98 35035591 return found;
99 }
100
101 720562251 void Insert(const Key &key, const Value &value) {
102 720562251 static_cast<Derived *>(this)->Grow(); // No-op if fixed-size
103 718182259 const bool overwritten = DoInsert(key, value, true);
104 717475625 size_ += !overwritten; // size + 1 if the key was not yet in the map
105 717475625 }
106
107 40744912 bool Erase(const Key &key) {
108 uint32_t bucket;
109 uint32_t collisions;
110
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 40744912 const bool found = DoLookup(key, &bucket, &collisions);
111
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 40299492 if (found) {
112 40303572 keys_[bucket] = empty_key_;
113 40303572 size_--;
114 40303572 bucket = (bucket + 1) % capacity_;
115
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 109754424 while (!(keys_[bucket] == empty_key_)) {
116 70032059 Key rehash = keys_[bucket];
117 70032059 keys_[bucket] = empty_key_;
118
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 70032059 DoInsert(rehash, values_[bucket], false);
119 69450852 bucket = (bucket + 1) % capacity_;
120 }
121
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 39722365 static_cast<Derived *>(this)->Shrink(); // No-op if fixed-size
122 }
123 40228827 return found;
124 }
125
126 711 void Clear() { DoClear(true); }
127
128 1690 uint64_t bytes_allocated() const { return bytes_allocated_; }
129 273 static double GetEntrySize() {
130 546 const double unit = sizeof(Key) + sizeof(Value);
131 546 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 80418 Key empty_key() const { return empty_key_; }
143 176970 Key *keys() const { return keys_; }
144 172 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 1039638533 uint32_t ScaleHash(const Key &key) const {
151 1039638533 const double bucket = (static_cast<double>(hasher_(key))
152 1032812591 * static_cast<double>(capacity_)
153 / static_cast<double>(static_cast<uint32_t>(-1)));
154 1032812591 return static_cast<uint32_t>(bucket) % capacity_;
155 }
156
157 162142 void AllocMemory() {
158 162142 keys_ = static_cast<Key *>(smmap(capacity_ * sizeof(Key)));
159 162164 values_ = static_cast<Value *>(smmap(capacity_ * sizeof(Value)));
160
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 1868322852 for (uint32_t i = 0; i < capacity_; ++i) {
161 1868160688 /*keys_[i] =*/new (keys_ + i) Key();
162 }
163
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 1869412600 for (uint32_t i = 0; i < capacity_; ++i) {
164 1869352318 /*values_[i] =*/new (values_ + i) Value();
165 }
166 104645 bytes_allocated_ = (sizeof(Key) + sizeof(Value)) * capacity_;
167 104645 }
168
169 162026 void DeallocMemory(Key *k, Value *v, uint32_t c) {
170
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 1873778034 for (uint32_t i = 0; i < c; ++i) {
171 1873616008 k[i].~Key();
172 }
173
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 1875940964 for (uint32_t i = 0; i < c; ++i) {
174 1875778938 v[i].~Value();
175 }
176
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 162026 if (k)
177 162004 smunmap(k);
178
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 162048 if (v)
179 162026 smunmap(v);
180 162048 k = NULL;
181 162048 v = NULL;
182 162048 }
183
184 // Returns true iff the key is overwritten
185 840519517 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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 840519517 const bool overwritten = DoLookup(key, &bucket, &collisions);
190
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 840239443 if (count_collisions) {
191 718073365 num_collisions_ += collisions;
192 718073365 max_collisions_ = std::max(collisions, max_collisions_);
193 }
194 839771481 keys_[bucket] = key;
195
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 839771481 values_[bucket] = value;
196 839771481 return overwritten;
197 }
198
199 1042974503 bool DoLookup(const Key &key, uint32_t *bucket, uint32_t *collisions) const {
200 1042974503 *bucket = ScaleHash(key);
201 1032006905 *collisions = 0;
202
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 10639779107 while (!(keys_[*bucket] == empty_key_)) {
203
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 9810431069 if (keys_[*bucket] == key)
204 202658867 return true;
205 9607772202 *bucket = (*bucket + 1) % capacity_;
206 9607772202 (*collisions)++;
207 }
208 829348038 return false;
209 }
210
211 162194 void DoClear(const bool reset_capacity) {
212
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 162194 if (reset_capacity)
213 1188 static_cast<Derived *>(this)->ResetCapacity(); // No-op if fixed-size
214
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 1869891028 for (uint32_t i = 0; i < capacity_; ++i)
215 1869728834 keys_[i] = empty_key_;
216 162194 size_ = 0;
217 162194 }
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 1660 void SetThresholds() { }
247 113525 void Grow() { }
248 20176 void Shrink() { }
249 30 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 110502 SmallHashDynamic() : Base() {
264 110502 num_migrates_ = 0;
265
266 // Properly set by Init
267 110502 threshold_grow_ = 0;
268 110502 threshold_shrink_ = 0;
269 110502 }
270
271 SmallHashDynamic(const SmallHashDynamic<Key, Value> &other) : Base() {
272 num_migrates_ = 0;
273 CopyFrom(other);
274 }
275
276 355 SmallHashDynamic<Key, Value> &operator=(
277 const SmallHashDynamic<Key, Value> &other) {
278
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 355 if (&other == this)
279 ✗ return *this;
280
281 355 CopyFrom(other);
282 355 return *this;
283 }
284
285 21526938 uint32_t capacity() const { return Base::capacity_; }
286 409680845 uint32_t size() const { return Base::size_; }
287 uint32_t num_migrates() const { return num_migrates_; }
288
289 protected:
290 160504 void SetThresholds() {
291 160504 threshold_grow_ = static_cast<uint32_t>(static_cast<double>(capacity())
292 160482 * kThresholdGrow);
293 160482 threshold_shrink_ = static_cast<uint32_t>(static_cast<double>(capacity())
294 160482 * kThresholdShrink);
295 160482 }
296
297 719677839 void Grow() {
298
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 719677839 if (size() > threshold_grow_)
299 33712 Migrate(capacity() * 2);
300 718572775 }
301
302 40168832 void Shrink() {
303
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 40168832 if (size() < threshold_shrink_) {
304 10443629 const uint32_t target_capacity = capacity() / 2;
305
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 10443065 if (target_capacity >= Base::initial_capacity_)
306 7546 Migrate(target_capacity);
307 }
308 40161719 }
309
310 1158 void ResetCapacity() {
311 1158 Base::DeallocMemory(Base::keys_, Base::values_, Base::capacity_);
312 1158 Base::capacity_ = Base::initial_capacity_;
313 1158 Base::AllocMemory();
314 1158 SetThresholds();
315 1158 }
316
317 private:
318 // Returns a random permutation of indices [0..N-1] that is allocated
319 // by smmap (Knuth's shuffle algorithm)
320 15502 uint32_t *ShuffleIndices(const uint32_t N) {
321 15502 uint32_t *shuffled = static_cast<uint32_t *>(smmap(N * sizeof(uint32_t)));
322 // Init with identity
323
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 247401902 for (unsigned i = 0; i < N; ++i)
324 247386400 shuffled[i] = i;
325 // Shuffle (no shuffling for the last element)
326
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 236034620 for (unsigned i = 0; i < N - 1; ++i) {
327 235285044 const uint32_t swap_idx = i + g_prng.Next(N - i);
328 236019118 const uint32_t tmp = shuffled[i];
329 236019118 shuffled[i] = shuffled[swap_idx];
330 236019118 shuffled[swap_idx] = tmp;
331 }
332 749576 return shuffled;
333 }
334
335 48804 void Migrate(const uint32_t new_capacity) {
336 48804 Key *old_keys = Base::keys_;
337 48804 Value *old_values = Base::values_;
338 48804 const uint32_t old_capacity = capacity();
339 48826 const uint32_t old_size = size();
340
341 48848 Base::capacity_ = new_capacity;
342 48848 SetThresholds();
343 48826 Base::AllocMemory();
344 48848 Base::DoClear(false);
345
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 48848 if (new_capacity < old_capacity) {
346 15136 uint32_t *shuffled_indices = ShuffleIndices(old_capacity);
347
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 211480258 for (uint32_t i = 0; i < old_capacity; ++i) {
348
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 211494624 if (old_keys[shuffled_indices[i]] != Base::empty_key_) {
349 53055398 Base::Insert(old_keys[shuffled_indices[i]],
350 53055398 old_values[shuffled_indices[i]]);
351 }
352 }
353 ✗ smunmap(shuffled_indices);
354 } else {
355
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 414135684 for (uint32_t i = 0; i < old_capacity; ++i) {
356
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 414114930 if (old_keys[i] != Base::empty_key_)
357 310697516 Base::Insert(old_keys[i], old_values[i]);
358 }
359 }
360
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 35890 assert(size() == old_size);
361
362 48848 Base::DeallocMemory(old_keys, old_values, old_capacity);
363 48848 num_migrates_++;
364 48848 }
365
366 355 void CopyFrom(const SmallHashDynamic<Key, Value> &other) {
367 355 uint32_t *shuffled_indices = ShuffleIndices(other.capacity_);
368
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 15146395 for (uint32_t i = 0; i < other.capacity_; ++i) {
369
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 15146040 if (other.keys_[shuffled_indices[i]] != other.empty_key_) {
370 11000000 this->Insert(other.keys_[shuffled_indices[i]],
371 11000000 other.values_[shuffled_indices[i]]);
372 }
373 }
374 355 smunmap(shuffled_indices);
375 355 }
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:
391 110 MultiHash() {
392 110 num_hashmaps_ = 0;
393 110 hashmaps_ = NULL;
394 110 locks_ = NULL;
395 110 }
396
397 110 void Init(const uint8_t num_hashmaps, const Key &empty_key,
398 uint32_t (*hasher)(const Key &key)) {
399
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 110 assert(num_hashmaps > 0);
400 110 const uint8_t N = num_hashmaps;
401 110 num_hashmaps_ = N;
402
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 4730 hashmaps_ = new SmallHashDynamic<Key, Value>[N]();
403 110 locks_ = static_cast<pthread_mutex_t *>(
404 110 smalloc(N * sizeof(pthread_mutex_t)));
405
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 4730 for (uint8_t i = 0; i < N; ++i) {
406 4620 int retval = pthread_mutex_init(&locks_[i], NULL);
407
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 4620 assert(retval == 0);
408 4620 hashmaps_[i].Init(128, empty_key, hasher);
409 }
410 110 }
411
412 110 ~MultiHash() {
413
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 4730 for (uint8_t i = 0; i < num_hashmaps_; ++i) {
414 4620 pthread_mutex_destroy(&locks_[i]);
415 }
416 110 free(locks_);
417
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 4730 delete[] hashmaps_;
418 110 }
419
420 11000000 bool Lookup(const Key &key, Value *value) {
421 11000000 uint8_t target = SelectHashmap(key);
422 11000000 Lock(target);
423 11000000 const bool result = hashmaps_[target].Lookup(key, value);
424 11000000 Unlock(target);
425 11000000 return result;
426 }
427
428 41087717 void Insert(const Key &key, const Value &value) {
429 41087717 uint8_t target = SelectHashmap(key);
430 40051132 Lock(target);
431 41594718 hashmaps_[target].Insert(key, value);
432 39350685 Unlock(target);
433 42764667 }
434
435 19874657 void Erase(const Key &key) {
436 19874657 uint8_t target = SelectHashmap(key);
437 19089818 Lock(target);
438 20300555 hashmaps_[target].Erase(key);
439 18732417 Unlock(target);
440 20562014 }
441
442 11 void Clear() {
443
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 473 for (uint8_t i = 0; i < num_hashmaps_; ++i)
444 462 Lock(i);
445
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 473 for (uint8_t i = 0; i < num_hashmaps_; ++i)
446 462 hashmaps_[i].Clear();
447
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 473 for (uint8_t i = 0; i < num_hashmaps_; ++i)
448 462 Unlock(i);
449 11 }
450
451 110 uint8_t num_hashmaps() const { return num_hashmaps_; }
452
453 88 void GetSizes(uint32_t *sizes) {
454
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 3784 for (uint8_t i = 0; i < num_hashmaps_; ++i) {
455 3696 Lock(i);
456 3696 sizes[i] = hashmaps_[i].size();
457 3696 Unlock(i);
458 }
459 88 }
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 71482554 inline uint8_t SelectHashmap(const Key &key) {
471 71482554 uint32_t hash = MurmurHash2(&key, sizeof(key), 0x37);
472 70399318 double bucket = static_cast<double>(hash)
473 70399318 * static_cast<double>(num_hashmaps_)
474 / static_cast<double>(static_cast<uint32_t>(-1));
475 70399318 return static_cast<uint32_t>(bucket) % num_hashmaps_;
476 }
477
478 69862540 inline void Lock(const uint8_t target) {
479 69862540 int retval = pthread_mutex_lock(&locks_[target]);
480
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 75489414 assert(retval == 0);
481 75489414 }
482
483 68992880 inline void Unlock(const uint8_t target) {
484 68992880 int retval = pthread_mutex_unlock(&locks_[target]);
485
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 75704563 assert(retval == 0);
486 75704563 }
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