/*
* Copyright 2006 The Android Open Source Project
*
* Hash table. The dominant calls are add and lookup, with removals
* happening very infrequently. We use probing, and don't worry much
* about tombstone removal.
*/
#include <stdlib.h>
#include <assert.h>
#define LOG_TAG "minzip"
#include "Log.h"
#include "Hash.h"
/* table load factor, i.e. how full can it get before we resize */
//#define LOAD_NUMER 3 // 75%
//#define LOAD_DENOM 4
#define LOAD_NUMER 5 // 62.5%
#define LOAD_DENOM 8
//#define LOAD_NUMER 1 // 50%
//#define LOAD_DENOM 2
/*
* Compute the capacity needed for a table to hold "size" elements.
*/
size_t mzHashSize(size_t size) {
return (size * LOAD_DENOM) / LOAD_NUMER +1;
}
/*
* Round up to the next highest power of 2.
*
* Found on http://graphics.stanford.edu/~seander/bithacks.html.
*/
unsigned int roundUpPower2(unsigned int val)
{
val--;
val |= val >> 1;
val |= val >> 2;
val |= val >> 4;
val |= val >> 8;
val |= val >> 16;
val++;
return val;
}
/*
* Create and initialize a hash table.
*/
HashTable* mzHashTableCreate(size_t initialSize, HashFreeFunc freeFunc)
{
HashTable* pHashTable;
assert(initialSize > 0);
pHashTable = (HashTable*) malloc(sizeof(*pHashTable));
if (pHashTable == NULL)
return NULL;
pHashTable->tableSize = roundUpPower2(initialSize);
pHashTable->numEntries = pHashTable->numDeadEntries = 0;
pHashTable->freeFunc = freeFunc;
pHashTable->pEntries =
(HashEntry*) calloc((size_t)pHashTable->tableSize, sizeof(HashTable));
if (pHashTable->pEntries == NULL) {
free(pHashTable);
return NULL;
}
return pHashTable;
}
/*
* Clear out all entries.
*/
void mzHashTableClear(HashTable* pHashTable)
{
HashEntry* pEnt;
int i;
pEnt = pHashTable->pEntries;
for (i = 0; i < pHashTable->tableSize; i++, pEnt++) {
if (pEnt->data == HASH_TOMBSTONE) {
// nuke entry
pEnt->data = NULL;
} else if (pEnt->data != NULL) {
// call free func then nuke entry
if (pHashTable->freeFunc != NULL)
(*pHashTable->freeFunc)(pEnt->data);
pEnt->data = NULL;
}
}
pHashTable->numEntries = 0;
pHashTable->numDeadEntries = 0;
}
/*
* Free the table.
*/
void mzHashTableFree(HashTable* pHashTable)
{
if (pHashTable == NULL)
return;
mzHashTableClear(pHashTable);
free(pHashTable->pEntries);
free(pHashTable);
}
#ifndef NDEBUG
/*
* Count up the number of tombstone entries in the hash table.
*/
static int countTombStones(HashTable* pHashTable)
{
int i, count;
for (count = i = 0; i < pHashTable->tableSize; i++) {
if (pHashTable->pEntries[i].data == HASH_TOMBSTONE)
count++;
}
return count;
}
#endif
/*
* Resize a hash table. We do this when adding an entry increased the
* size of the table beyond its comfy limit.
*
* This essentially requires re-inserting all elements into the new storage.
*
* If multiple threads can access the hash table, the table's lock should
* have been grabbed before issuing the "lookup+add" call that led to the
* resize, so we don't have a synchronization problem here.
*/
static bool resizeHash(HashTable* pHashTable, int newSize)
{
HashEntry* pNewEntries;
int i;
assert(countTombStones(pHashTable) == pHashTable->numDeadEntries);
pNewEntries = (HashEntry*) calloc(newSize, sizeof(HashTable));
if (pNewEntries == NULL)
return false;
for (i = 0; i < pHashTable->tableSize; i++) {
void* data = pHashTable->pEntries[i].data;
if (data != NULL && data != HASH_TOMBSTONE) {
int hashValue = pHashTable->pEntries[i].hashValue;
int newIdx;
/* probe for new spot, wrapping around */
newIdx = hashValue & (newSize-1);
while (pNewEntries[newIdx].data != NULL)
newIdx = (newIdx + 1) & (newSize-1);
pNewEntries[newIdx].hashValue = hashValue;
pNewEntries[newIdx].data = data;
}
}
free(pHashTable->pEntries);
pHashTable->pEntries = pNewEntries;
pHashTable->tableSize = newSize;
pHashTable->numDeadEntries = 0;
assert(countTombStones(pHashTable) == 0);
return true;
}
/*
* Look up an entry.
*
* We probe on collisions, wrapping around the table.
*/
void* mzHashTableLookup(HashTable* pHashTable, unsigned int itemHash, void* item,
HashCompareFunc cmpFunc, bool doAdd)
{
HashEntry* pEntry;
HashEntry* pEnd;
void* result = NULL;
assert(pHashTable->tableSize > 0);
assert(item != HASH_TOMBSTONE);
assert(item != NULL);
/* jump to the first entry and probe for a match */
pEntry = &pHashTable->pEntries[itemHash & (pHashTable->tableSize-1)];
pEnd = &pHashTable->pEntries[pHashTable->tableSize];
while (pEntry->data != NULL) {
if (pEntry->data != HASH_TOMBSTONE &&
pEntry->hashValue == itemHash &&
(*cmpFunc)(pEntry->data, item) == 0)
{
/* match */
break;
}
pEntry++;
if (pEntry == pEnd) { /* wrap around to start */
if (pHashTable->tableSize == 1)
break; /* edge case - single-entry table */
pEntry = pHashTable->pEntries;
}
}
if (pEntry->data == NULL) {
if (doAdd) {
pEntry->hashValue = itemHash;
pEntry->data = item;
pHashTable->numEntries++;
/*
* We've added an entry. See if this brings us too close to full.
*/
if ((pHashTable->numEntries+pHashTable->numDeadEntries) * LOAD_DENOM
> pHashTable->tableSize * LOAD_NUMER)
{
if (!resizeHash(pHashTable, pHashTable->tableSize * 2)) {
/* don't really have a way to indicate failure */
LOGE("Dalvik hash resize failure\n");
abort();
}
/* note "pEntry" is now invalid */
}
/* full table is bad -- search for nonexistent never halts */
assert(pHashTable->numEntries < pHashTable->tableSize);
result = item;
} else {
assert(result == NULL);
}
} else {
result = pEntry->data;
}
return result;
}
/*
* Remove an entry from the table.
*
* Does NOT invoke the "free" function on the item.
*/
bool mzHashTableRemove(HashTable* pHashTable, unsigned int itemHash, void* item)
{
HashEntry* pEntry;
HashEntry* pEnd;
assert(pHashTable->tableSize > 0);
/* jump to the first entry and probe for a match */
pEntry = &pHashTable->pEntries[itemHash & (pHashTable->tableSize-1)];
pEnd = &pHashTable->pEntries[pHashTable->tableSize];
while (pEntry->data != NULL) {
if (pEntry->data == item) {
pEntry->data = HASH_TOMBSTONE;
pHashTable->numEntries--;
pHashTable->numDeadEntries++;
return true;
}
pEntry++;
if (pEntry == pEnd) { /* wrap around to start */
if (pHashTable->tableSize == 1)
break; /* edge case - single-entry table */
pEntry = pHashTable->pEntries;
}
}
return false;
}
/*
* Execute a function on every entry in the hash table.
*
* If "func" returns a nonzero value, terminate early and return the value.
*/
int mzHashForeach(HashTable* pHashTable, HashForeachFunc func, void* arg)
{
int i, val;
for (i = 0; i < pHashTable->tableSize; i++) {
HashEntry* pEnt = &pHashTable->pEntries[i];
if (pEnt->data != NULL && pEnt->data != HASH_TOMBSTONE) {
val = (*func)(pEnt->data, arg);
if (val != 0)
return val;
}
}
return 0;
}
/*
* Look up an entry, counting the number of times we have to probe.
*
* Returns -1 if the entry wasn't found.
*/
int countProbes(HashTable* pHashTable, unsigned int itemHash, const void* item,
HashCompareFunc cmpFunc)
{
HashEntry* pEntry;
HashEntry* pEnd;
int count = 0;
assert(pHashTable->tableSize > 0);
assert(item != HASH_TOMBSTONE);
assert(item != NULL);
/* jump to the first entry and probe for a match */
pEntry = &pHashTable->pEntries[itemHash & (pHashTable->tableSize-1)];
pEnd = &pHashTable->pEntries[pHashTable->tableSize];
while (pEntry->data != NULL) {
if (pEntry->data != HASH_TOMBSTONE &&
pEntry->hashValue == itemHash &&
(*cmpFunc)(pEntry->data, item) == 0)
{
/* match */
break;
}
pEntry++;
if (pEntry == pEnd) { /* wrap around to start */
if (pHashTable->tableSize == 1)
break; /* edge case - single-entry table */
pEntry = pHashTable->pEntries;
}
count++;
}
if (pEntry->data == NULL)
return -1;
return count;
}
/*
* Evaluate the amount of probing required for the specified hash table.
*
* We do this by running through all entries in the hash table, computing
* the hash value and then doing a lookup.
*
* The caller should lock the table before calling here.
*/
void mzHashTableProbeCount(HashTable* pHashTable, HashCalcFunc calcFunc,
HashCompareFunc cmpFunc)
{
int numEntries, minProbe, maxProbe, totalProbe;
HashIter iter;
numEntries = maxProbe = totalProbe = 0;
minProbe = 65536*32767;
for (mzHashIterBegin(pHashTable, &iter); !mzHashIterDone(&iter);
mzHashIterNext(&iter))
{
const void* data = (const void*)mzHashIterData(&iter);
int count;
count = countProbes(pHashTable, (*calcFunc)(data), data, cmpFunc);
numEntries++;
if (count < minProbe)
minProbe = count;
if (count > maxProbe)
maxProbe = count;
totalProbe += count;
}
LOGV("Probe: min=%d max=%d, total=%d in %d (%d), avg=%.3f\n",
minProbe, maxProbe, totalProbe, numEntries, pHashTable->tableSize,
(float) totalProbe / (float) numEntries);
}
