diff --git a/src/dict.c b/src/dict.c index 66bb983a83aaf426bac9ab0cea93d8d0d03c4212..ec58e820073065dbee96d69a1d1a8135f2ef3f7a 100644 --- a/src/dict.c +++ b/src/dict.c @@ -85,29 +85,73 @@ unsigned int dictIdentityHashFunction(unsigned int key) return key; } -static int dict_hash_function_seed = 5381; +static uint32_t dict_hash_function_seed = 5381; -void dictSetHashFunctionSeed(unsigned int seed) { +void dictSetHashFunctionSeed(uint32_t seed) { dict_hash_function_seed = seed; } -unsigned int dictGetHashFunctionSeed(void) { +uint32_t dictGetHashFunctionSeed(void) { return dict_hash_function_seed; } -/* 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 = 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; - while (len--) - hash = ((hash << 5) + hash) + (*buf++); /* hash * 33 + c */ - return hash; + /* 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 = dict_hash_function_seed; + unsigned int hash = (unsigned int)dict_hash_function_seed; while (len--) hash = ((hash << 5) + hash) + (tolower(*buf++)); /* hash * 33 + c */ diff --git a/src/dict.h b/src/dict.h index 5f85695354471b29ab074f974368a673a5bfc45b..f480ae539232fbe374feeb96661a3088d8b12e20 100644 --- a/src/dict.h +++ b/src/dict.h @@ -155,7 +155,7 @@ dictEntry *dictNext(dictIterator *iter); void dictReleaseIterator(dictIterator *iter); dictEntry *dictGetRandomKey(dict *d); void dictPrintStats(dict *d); -unsigned int dictGenHashFunction(const unsigned char *buf, int len); +unsigned int dictGenHashFunction(const void *key, int len); unsigned int dictGenCaseHashFunction(const unsigned char *buf, int len); void dictEmpty(dict *d); void dictEnableResize(void);