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      1 /*
      2  * Copyright 2006 The Android Open Source Project
      3  *
      4  * Hash table.  The dominant calls are add and lookup, with removals
      5  * happening very infrequently.  We use probing, and don't worry much
      6  * about tombstone removal.
      7  */
      8 #include <stdlib.h>
      9 #include <assert.h>
     10 
     11 #define LOG_TAG "minzip"
     12 #include "Log.h"
     13 #include "Hash.h"
     14 
     15 /* table load factor, i.e. how full can it get before we resize */
     16 //#define LOAD_NUMER  3       // 75%
     17 //#define LOAD_DENOM  4
     18 #define LOAD_NUMER  5       // 62.5%
     19 #define LOAD_DENOM  8
     20 //#define LOAD_NUMER  1       // 50%
     21 //#define LOAD_DENOM  2
     22 
     23 /*
     24  * Compute the capacity needed for a table to hold "size" elements.
     25  */
     26 size_t mzHashSize(size_t size) {
     27     return (size * LOAD_DENOM) / LOAD_NUMER +1;
     28 }
     29 
     30 /*
     31  * Round up to the next highest power of 2.
     32  *
     33  * Found on http://graphics.stanford.edu/~seander/bithacks.html.
     34  */
     35 unsigned int roundUpPower2(unsigned int val)
     36 {
     37     val--;
     38     val |= val >> 1;
     39     val |= val >> 2;
     40     val |= val >> 4;
     41     val |= val >> 8;
     42     val |= val >> 16;
     43     val++;
     44 
     45     return val;
     46 }
     47 
     48 /*
     49  * Create and initialize a hash table.
     50  */
     51 HashTable* mzHashTableCreate(size_t initialSize, HashFreeFunc freeFunc)
     52 {
     53     HashTable* pHashTable;
     54 
     55     assert(initialSize > 0);
     56 
     57     pHashTable = (HashTable*) malloc(sizeof(*pHashTable));
     58     if (pHashTable == NULL)
     59         return NULL;
     60 
     61     pHashTable->tableSize = roundUpPower2(initialSize);
     62     pHashTable->numEntries = pHashTable->numDeadEntries = 0;
     63     pHashTable->freeFunc = freeFunc;
     64     pHashTable->pEntries =
     65         (HashEntry*) calloc((size_t)pHashTable->tableSize, sizeof(HashTable));
     66     if (pHashTable->pEntries == NULL) {
     67         free(pHashTable);
     68         return NULL;
     69     }
     70 
     71     return pHashTable;
     72 }
     73 
     74 /*
     75  * Clear out all entries.
     76  */
     77 void mzHashTableClear(HashTable* pHashTable)
     78 {
     79     HashEntry* pEnt;
     80     int i;
     81 
     82     pEnt = pHashTable->pEntries;
     83     for (i = 0; i < pHashTable->tableSize; i++, pEnt++) {
     84         if (pEnt->data == HASH_TOMBSTONE) {
     85             // nuke entry
     86             pEnt->data = NULL;
     87         } else if (pEnt->data != NULL) {
     88             // call free func then nuke entry
     89             if (pHashTable->freeFunc != NULL)
     90                 (*pHashTable->freeFunc)(pEnt->data);
     91             pEnt->data = NULL;
     92         }
     93     }
     94 
     95     pHashTable->numEntries = 0;
     96     pHashTable->numDeadEntries = 0;
     97 }
     98 
     99 /*
    100  * Free the table.
    101  */
    102 void mzHashTableFree(HashTable* pHashTable)
    103 {
    104     if (pHashTable == NULL)
    105         return;
    106     mzHashTableClear(pHashTable);
    107     free(pHashTable->pEntries);
    108     free(pHashTable);
    109 }
    110 
    111 #ifndef NDEBUG
    112 /*
    113  * Count up the number of tombstone entries in the hash table.
    114  */
    115 static int countTombStones(HashTable* pHashTable)
    116 {
    117     int i, count;
    118 
    119     for (count = i = 0; i < pHashTable->tableSize; i++) {
    120         if (pHashTable->pEntries[i].data == HASH_TOMBSTONE)
    121             count++;
    122     }
    123     return count;
    124 }
    125 #endif
    126 
    127 /*
    128  * Resize a hash table.  We do this when adding an entry increased the
    129  * size of the table beyond its comfy limit.
    130  *
    131  * This essentially requires re-inserting all elements into the new storage.
    132  *
    133  * If multiple threads can access the hash table, the table's lock should
    134  * have been grabbed before issuing the "lookup+add" call that led to the
    135  * resize, so we don't have a synchronization problem here.
    136  */
    137 static bool resizeHash(HashTable* pHashTable, int newSize)
    138 {
    139     HashEntry* pNewEntries;
    140     int i;
    141 
    142     assert(countTombStones(pHashTable) == pHashTable->numDeadEntries);
    143 
    144     pNewEntries = (HashEntry*) calloc(newSize, sizeof(HashTable));
    145     if (pNewEntries == NULL)
    146         return false;
    147 
    148     for (i = 0; i < pHashTable->tableSize; i++) {
    149         void* data = pHashTable->pEntries[i].data;
    150         if (data != NULL && data != HASH_TOMBSTONE) {
    151             int hashValue = pHashTable->pEntries[i].hashValue;
    152             int newIdx;
    153 
    154             /* probe for new spot, wrapping around */
    155             newIdx = hashValue & (newSize-1);
    156             while (pNewEntries[newIdx].data != NULL)
    157                 newIdx = (newIdx + 1) & (newSize-1);
    158 
    159             pNewEntries[newIdx].hashValue = hashValue;
    160             pNewEntries[newIdx].data = data;
    161         }
    162     }
    163 
    164     free(pHashTable->pEntries);
    165     pHashTable->pEntries = pNewEntries;
    166     pHashTable->tableSize = newSize;
    167     pHashTable->numDeadEntries = 0;
    168 
    169     assert(countTombStones(pHashTable) == 0);
    170     return true;
    171 }
    172 
    173 /*
    174  * Look up an entry.
    175  *
    176  * We probe on collisions, wrapping around the table.
    177  */
    178 void* mzHashTableLookup(HashTable* pHashTable, unsigned int itemHash, void* item,
    179     HashCompareFunc cmpFunc, bool doAdd)
    180 {
    181     HashEntry* pEntry;
    182     HashEntry* pEnd;
    183     void* result = NULL;
    184 
    185     assert(pHashTable->tableSize > 0);
    186     assert(item != HASH_TOMBSTONE);
    187     assert(item != NULL);
    188 
    189     /* jump to the first entry and probe for a match */
    190     pEntry = &pHashTable->pEntries[itemHash & (pHashTable->tableSize-1)];
    191     pEnd = &pHashTable->pEntries[pHashTable->tableSize];
    192     while (pEntry->data != NULL) {
    193         if (pEntry->data != HASH_TOMBSTONE &&
    194             pEntry->hashValue == itemHash &&
    195             (*cmpFunc)(pEntry->data, item) == 0)
    196         {
    197             /* match */
    198             break;
    199         }
    200 
    201         pEntry++;
    202         if (pEntry == pEnd) {     /* wrap around to start */
    203             if (pHashTable->tableSize == 1)
    204                 break;      /* edge case - single-entry table */
    205             pEntry = pHashTable->pEntries;
    206         }
    207     }
    208 
    209     if (pEntry->data == NULL) {
    210         if (doAdd) {
    211             pEntry->hashValue = itemHash;
    212             pEntry->data = item;
    213             pHashTable->numEntries++;
    214 
    215             /*
    216              * We've added an entry.  See if this brings us too close to full.
    217              */
    218             if ((pHashTable->numEntries+pHashTable->numDeadEntries) * LOAD_DENOM
    219                 > pHashTable->tableSize * LOAD_NUMER)
    220             {
    221                 if (!resizeHash(pHashTable, pHashTable->tableSize * 2)) {
    222                     /* don't really have a way to indicate failure */
    223                     LOGE("Dalvik hash resize failure\n");
    224                     abort();
    225                 }
    226                 /* note "pEntry" is now invalid */
    227             }
    228 
    229             /* full table is bad -- search for nonexistent never halts */
    230             assert(pHashTable->numEntries < pHashTable->tableSize);
    231             result = item;
    232         } else {
    233             assert(result == NULL);
    234         }
    235     } else {
    236         result = pEntry->data;
    237     }
    238 
    239     return result;
    240 }
    241 
    242 /*
    243  * Remove an entry from the table.
    244  *
    245  * Does NOT invoke the "free" function on the item.
    246  */
    247 bool mzHashTableRemove(HashTable* pHashTable, unsigned int itemHash, void* item)
    248 {
    249     HashEntry* pEntry;
    250     HashEntry* pEnd;
    251 
    252     assert(pHashTable->tableSize > 0);
    253 
    254     /* jump to the first entry and probe for a match */
    255     pEntry = &pHashTable->pEntries[itemHash & (pHashTable->tableSize-1)];
    256     pEnd = &pHashTable->pEntries[pHashTable->tableSize];
    257     while (pEntry->data != NULL) {
    258         if (pEntry->data == item) {
    259             pEntry->data = HASH_TOMBSTONE;
    260             pHashTable->numEntries--;
    261             pHashTable->numDeadEntries++;
    262             return true;
    263         }
    264 
    265         pEntry++;
    266         if (pEntry == pEnd) {     /* wrap around to start */
    267             if (pHashTable->tableSize == 1)
    268                 break;      /* edge case - single-entry table */
    269             pEntry = pHashTable->pEntries;
    270         }
    271     }
    272 
    273     return false;
    274 }
    275 
    276 /*
    277  * Execute a function on every entry in the hash table.
    278  *
    279  * If "func" returns a nonzero value, terminate early and return the value.
    280  */
    281 int mzHashForeach(HashTable* pHashTable, HashForeachFunc func, void* arg)
    282 {
    283     int i, val;
    284 
    285     for (i = 0; i < pHashTable->tableSize; i++) {
    286         HashEntry* pEnt = &pHashTable->pEntries[i];
    287 
    288         if (pEnt->data != NULL && pEnt->data != HASH_TOMBSTONE) {
    289             val = (*func)(pEnt->data, arg);
    290             if (val != 0)
    291                 return val;
    292         }
    293     }
    294 
    295     return 0;
    296 }
    297 
    298 
    299 /*
    300  * Look up an entry, counting the number of times we have to probe.
    301  *
    302  * Returns -1 if the entry wasn't found.
    303  */
    304 int countProbes(HashTable* pHashTable, unsigned int itemHash, const void* item,
    305     HashCompareFunc cmpFunc)
    306 {
    307     HashEntry* pEntry;
    308     HashEntry* pEnd;
    309     int count = 0;
    310 
    311     assert(pHashTable->tableSize > 0);
    312     assert(item != HASH_TOMBSTONE);
    313     assert(item != NULL);
    314 
    315     /* jump to the first entry and probe for a match */
    316     pEntry = &pHashTable->pEntries[itemHash & (pHashTable->tableSize-1)];
    317     pEnd = &pHashTable->pEntries[pHashTable->tableSize];
    318     while (pEntry->data != NULL) {
    319         if (pEntry->data != HASH_TOMBSTONE &&
    320             pEntry->hashValue == itemHash &&
    321             (*cmpFunc)(pEntry->data, item) == 0)
    322         {
    323             /* match */
    324             break;
    325         }
    326 
    327         pEntry++;
    328         if (pEntry == pEnd) {     /* wrap around to start */
    329             if (pHashTable->tableSize == 1)
    330                 break;      /* edge case - single-entry table */
    331             pEntry = pHashTable->pEntries;
    332         }
    333 
    334         count++;
    335     }
    336     if (pEntry->data == NULL)
    337         return -1;
    338 
    339     return count;
    340 }
    341 
    342 /*
    343  * Evaluate the amount of probing required for the specified hash table.
    344  *
    345  * We do this by running through all entries in the hash table, computing
    346  * the hash value and then doing a lookup.
    347  *
    348  * The caller should lock the table before calling here.
    349  */
    350 void mzHashTableProbeCount(HashTable* pHashTable, HashCalcFunc calcFunc,
    351     HashCompareFunc cmpFunc)
    352 {
    353     int numEntries, minProbe, maxProbe, totalProbe;
    354     HashIter iter;
    355 
    356     numEntries = maxProbe = totalProbe = 0;
    357     minProbe = 65536*32767;
    358 
    359     for (mzHashIterBegin(pHashTable, &iter); !mzHashIterDone(&iter);
    360         mzHashIterNext(&iter))
    361     {
    362         const void* data = (const void*)mzHashIterData(&iter);
    363         int count;
    364 
    365         count = countProbes(pHashTable, (*calcFunc)(data), data, cmpFunc);
    366 
    367         numEntries++;
    368 
    369         if (count < minProbe)
    370             minProbe = count;
    371         if (count > maxProbe)
    372             maxProbe = count;
    373         totalProbe += count;
    374     }
    375 
    376     LOGV("Probe: min=%d max=%d, total=%d in %d (%d), avg=%.3f\n",
    377         minProbe, maxProbe, totalProbe, numEntries, pHashTable->tableSize,
    378         (float) totalProbe / (float) numEntries);
    379 }
    380