return key;
}
-/* Generic hash function (a popular one from Bernstein).
- * I tested a few and this was the best. */
-unsigned int dictGenHashFunction(const unsigned char *buf, int len) {
- unsigned int hash = 5381;
+static uint32_t dict_hash_function_seed = 5381;
- while (len--)
- hash = ((hash << 5) + hash) + (*buf++); /* hash * 33 + c */
- return hash;
+void dictSetHashFunctionSeed(uint32_t seed) {
+ dict_hash_function_seed = seed;
+}
+
+uint32_t dictGetHashFunctionSeed(void) {
+ return dict_hash_function_seed;
+}
+
+/* MurmurHash2, by Austin Appleby
+ * Note - This code makes a few assumptions about how your machine behaves -
+ * 1. We can read a 4-byte value from any address without crashing
+ * 2. sizeof(int) == 4
+ *
+ * And it has a few limitations -
+ *
+ * 1. It will not work incrementally.
+ * 2. It will not produce the same results on little-endian and big-endian
+ * machines.
+ */
+unsigned int dictGenHashFunction(const void *key, int len) {
+ /* 'm' and 'r' are mixing constants generated offline.
+ They're not really 'magic', they just happen to work well. */
+ uint32_t seed = dict_hash_function_seed;
+ const uint32_t m = 0x5bd1e995;
+ const int r = 24;
+
+ /* Initialize the hash to a 'random' value */
+ uint32_t h = seed ^ len;
+
+ /* Mix 4 bytes at a time into the hash */
+ const unsigned char *data = (const unsigned char *)key;
+
+ while(len >= 4) {
+ uint32_t k = *(uint32_t*)data;
+
+ k *= m;
+ k ^= k >> r;
+ k *= m;
+
+ h *= m;
+ h ^= k;
+
+ data += 4;
+ len -= 4;
+ }
+
+ /* Handle the last few bytes of the input array */
+ switch(len) {
+ case 3: h ^= data[2] << 16;
+ case 2: h ^= data[1] << 8;
+ case 1: h ^= data[0]; h *= m;
+ };
+
+ /* Do a few final mixes of the hash to ensure the last few
+ * bytes are well-incorporated. */
+ h ^= h >> 13;
+ h *= m;
+ h ^= h >> 15;
+
+ return (unsigned int)h;
}
-/* And a case insensitive version */
+/* And a case insensitive hash function (based on djb hash) */
unsigned int dictGenCaseHashFunction(const unsigned char *buf, int len) {
- unsigned int hash = 5381;
+ unsigned int hash = (unsigned int)dict_hash_function_seed;
while (len--)
hash = ((hash << 5) + hash) + (tolower(*buf++)); /* hash * 33 + c */
/* ----------------------------- API implementation ------------------------- */
-/* Reset an hashtable already initialized with ht_init().
- * NOTE: This function should only called by ht_destroy(). */
+/* Reset a hash table already initialized with ht_init().
+ * NOTE: This function should only be called by ht_destroy(). */
static void _dictReset(dictht *ht)
{
ht->table = NULL;
}
/* Resize the table to the minimal size that contains all the elements,
- * but with the invariant of a USER/BUCKETS ratio near to <= 1 */
+ * but with the invariant of a USED/BUCKETS ratio near to <= 1 */
int dictResize(dict *d)
{
int minimal;
return dictExpand(d, minimal);
}
-/* Expand or create the hashtable */
+/* Expand or create the hash table */
int dictExpand(dict *d, unsigned long size)
{
- dictht n; /* the new hashtable */
+ dictht n; /* the new hash table */
unsigned long realsize = _dictNextPower(size);
/* the size is invalid if it is smaller than the number of
- * elements already inside the hashtable */
+ * elements already inside the hash table */
if (dictIsRehashing(d) || d->ht[0].used > size)
return DICT_ERR;
- /* Allocate the new hashtable and initialize all pointers to NULL */
+ /* Allocate the new hash table and initialize all pointers to NULL */
n.size = realsize;
n.sizemask = realsize-1;
n.table = zcalloc(realsize*sizeof(dictEntry*));
* a value returns the dictEntry structure to the user, that will make
* sure to fill the value field as he wishes.
*
- * This function is also directly expoed to user API to be called
+ * This function is also directly exposed to user API to be called
* mainly in order to store non-pointers inside the hash value, example:
*
* entry = dictAddRaw(dict,mykey);
unsigned int h, idx, table;
dictEntry *he;
- /* Expand the hashtable if needed */
+ /* Expand the hash table if needed */
if (_dictExpandIfNeeded(d) == DICT_ERR)
return -1;
/* Compute the key hash value */
d->iterators = 0;
}
+void dictEnableResize(void) {
+ dict_can_resize = 1;
+}
+
+void dictDisableResize(void) {
+ dict_can_resize = 0;
+}
+
+#if 0
+
+/* The following is code that we don't use for Redis currently, but that is part
+of the library. */
+
+/* ----------------------- Debugging ------------------------*/
+
#define DICT_STATS_VECTLEN 50
static void _dictPrintStatsHt(dictht *ht) {
unsigned long i, slots = 0, chainlen, maxchainlen = 0;
}
}
-void dictEnableResize(void) {
- dict_can_resize = 1;
-}
-
-void dictDisableResize(void) {
- dict_can_resize = 0;
-}
-
-#if 0
-
-/* The following are just example hash table types implementations.
- * Not useful for Redis so they are commented out.
- */
-
/* ----------------------- StringCopy Hash Table Type ------------------------*/
static unsigned int _dictStringCopyHTHashFunction(const void *key)
projects / redis.git / blobdiff