These are a collection of general-purpose hash functions for strings. The string is passed by reference along with the length of the string.

unsigned int RSHash(char* str, unsigned int len) { unsigned int a = 63689; unsigned int b = 378551; unsigned int hash = 0; for (unsigned int i = 0; i < len; str++, i++) { hash = hash * a + (*str); a = a * b; } return hash; }

unsigned int JSHash(char* str, unsigned int len) { unsigned int hash = 1315423911; for (unsigned int i = 0; i < len; str++, i++) { hash ^= ((hash << 5) + (*str) + (hash >> 2)); } return hash; }

unsigned int PJWHash(char* str, unsigned int len) { const unsigned int BitsInUnsignedInt = (unsigned int)(sizeof(unsigned int) * 8); const unsigned int ThreeQuarters = (unsigned int)((BitsInUnsignedInt * 3) / 4); const unsigned int OneEighth = (unsigned int)(BitsInUnsignedInt / 8); const unsigned int HighBits = (unsigned int)(0xFFFFFFFF) << (BitsInUnsignedInt - OneEighth); unsigned int hash = 0; unsigned int test = 0; for (unsigned int i = 0; i < len; str++, i++) { hash = (hash << OneEighth) + (*str); if ((test = hash & HighBits) != 0) { hash = ((hash ^ (test >> ThreeQuarters)) & (~HighBits)); } } return hash; }

Similar to the Peter J. Weinberger hashing function but tweaked for 32-bit processors.

unsigned int ELFHash(char* str, unsigned int len) { unsigned int hash = 0; unsigned int x = 0; for (unsigned int = 0; i < len; str++, i++) { hash = (hash << 4) + (*str); if ((x = hash & 0xF0000000L) != 0) { hash ^= (x >> 24); } hash &= ~x; } return hash; }

unsigned int BKDRHash(char* str, unsigned int len) { unsigned int seed = 131; /* 31 131 1313 13131 131313 etc.. */ unsigned int hash = 0; for (unsigned int i = 0; i < len; str++, i++) { hash = (hash * seed) + (*str); } return hash; }

Used in the Open-Source `SDBM`

project and has a good overall distribution for different data sets. It works well in situations where there is a high variance in the most significant bits of elements in a data set.

unsigned int SDBMHash(char* str, unsigned int len) { unsigned int hash = 0; for (unsigned int i = 0; i < len; str++, i++) { hash = (*str) + (hash << 6) + (hash << 16) - hash; } return hash; }

unsigned int DJBHash(char* str, unsigned int len) { unsigned int hash = 5381; for (unsigned int i = 0; i < len; str++, i++) { hash = ((hash << 5) + hash) + (*str); } return hash; }

unsigned int DEKHash(char* str, unsigned int len) { unsigned int hash = len; for (unsigned int i = 0; i < len; str++, i++) { hash = ((hash << 5) ^ (hash >> 27)) ^ (*str); } return hash; }

From the FNV documentation.

fuss/hash_functions/strings.txt · Last modified: 2017/02/22 18:30 (external edit)

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