C code implementation of 10 classic string hash Functions

 

All content from: http://www.partow.net/programming/hashfunctions/

The following provides a total of 10 string hash functions. In the above link, you can find descriptions of each hash function and download some other information about the hash function.

The advantages and disadvantages of these hash functions are unknown. Among them, the elfhash function is widely used in UNIX systems and is also a string hash function recommended by the author in the competition of algorithm art and informatics. The dekhash function is introduced by knuth in the third volume of the art of computer programming.

Unsigned int RSHash (char * str, unsigned int len) <br/>{< br/> unsigned int B = 378551; <br/> unsigned int a = 63689; <br/> unsigned int hash = 0; <br/> unsigned int I = 0; <br/> for (I = 0; I <len; str ++, I ++) <br/>{< br/> hash = hash * a + (* str); <br/> a = a * B; <br/>}< br/> return hash; <br/>}< br/>/* End Of RS Hash Function */</p> <p> unsigned int JSHash (char * str, unsigned int len) <br/> {<br /> Unsigned int hash = 1315423911; <br/> unsigned int I = 0; <br/> for (I = 0; I <len; str ++, I ++) <br/>{< br/> hash ^ = (hash <5) + (* str) + (hash> 2 )); <br/>}< br/> return hash; <br/>}< br/>/* End Of JS Hash Function */</p> <p> unsigned int PJWHash (char * str, unsigned int len) <br/>{< br/> const unsigned int BitsInUnsignedInt = (unsigned int) (sizeof (unsigned int) * 8); <br/> const unsigned I Nt ThreeQuarters = (unsigned int) (BitsInUnsignedInt * 3)/4); <br/> const unsigned int OneEighth = (unsigned int) (BitsInUnsignedInt/8 ); <br/> const unsigned int HighBits = (unsigned int) (0 xFFFFFFFF) <(BitsInUnsignedInt-OneEighth); <br/> unsigned int hash = 0; <br/> unsigned int test = 0; <br/> unsigned int I = 0; <br/> for (I = 0; I <len; str ++, I ++) <br/>{< br/> hash = (hash <OneEighth) + (* Str); <br/> if (test = hash & HighBits )! = 0) <br/>{< br/> hash = (hash ^ (test> ThreeQuarters ))&(~ HighBits); <br/>}< br/> return hash; <br/>}< br/>/* End Of P. j. weinberger Hash Function */</p> <p> unsigned int ELFHash (char * str, unsigned int len) <br/>{< br/> unsigned int hash = 0; <br/> unsigned int x = 0; <br/> unsigned int I = 0; <br/> for (I = 0; I <len; str ++, I ++) <br/>{< br/> hash = (hash <4) + (* str ); <br/> if (x = hash & 0xF0000000L )! = 0) <br/>{< br/> hash ^ = (x> 24); <br/>}< br/> hash & = ~ X; <br/>}< br/> return hash; <br/>}< br/>/* End Of ELF Hash Function */</p> <p> unsigned int BKDRHash (char * str, unsigned int len) <br/>{< br/> unsigned int seed = 131;/* 31 131 1313 13131 131313 etc .. */<br/> unsigned int hash = 0; <br/> unsigned int I = 0; <br/> for (I = 0; I <len; str ++, I ++) <br/>{< br/> hash = (hash * seed) + (* str); <br/>}< br/> return hash; <br/>}< br/>/* End Of BKDR Hash Function */</p> <p> unsigned int SDBMHash (char * str, unsigned int len) <br/>{< br/> unsigned int hash = 0; <br/> unsigned int I = 0; <br/> for (I = 0; I <len; str ++, I ++) <br/> {<br/> hash = (* str) + (hash <6) + (hash <16)-hash; <br/>}< br/> return hash; <br/>}< br/>/* End Of SDBM Hash Function */</p> <p> unsigned int DJBHash (char * str, unsigned int len) <br/>{< br/> unsigned int hash = 5381; <Br/> unsigned int I = 0; <br/> for (I = 0; I <len; str ++, I ++) <br/>{< br/> hash = (hash <5) + hash) + (* str); <br/>}< br/> return hash; <br/>}< br/>/* End Of DJB Hash Function */</p> <p> unsigned int DEKHash (char * str, unsigned int len) <br/>{< br/> unsigned int hash = len; <br/> unsigned int I = 0; <br/> for (I = 0; I <len; str ++, I ++) <br/>{< br/> hash = (hash <5) ^ (hash> 27) ^ (* s Tr); <br/>}< br/> return hash; <br/>}< br/>/* End Of DEK Hash Function */</p> <p> unsigned int BPHash (char * str, unsigned int len) <br/>{< br/> unsigned int hash = 0; <br/> unsigned int I = 0; <br/> for (I = 0; I <len; str ++, I ++) <br/>{< br/> hash = hash <7 ^ (* str ); <br/>}< br/> return hash; <br/>}< br/>/* End Of BP Hash Function */</p> <p> unsigned int FNVHash (char * str, unsigned int len) <br/ >{< Br/> const unsigned int fnv_prime = 0x811C9DC5; <br/> unsigned int hash = 0; <br/> unsigned int I = 0; <br/> for (I = 0; I <len; str ++, I ++) <br/>{< br/> hash * = fnv_prime; <br/> hash ^ = (* str); <br/>}< br/> return hash; <br/>}< br/>/* End Of FNV Hash Function */</p> <p> unsigned int APHash (char * str, unsigned int len) <br/>{< br/> unsigned int hash = 0 xAAAAAAAA; <br/> unsigned int I = 0; <br/> For (I = 0; I <len; str ++, I ++) <br/>{< br/> hash ^ = (I & 1) = 0 )? (Hash <7) ^ (* str) * (hash> 3): <br/> (~ (Hash <11) + (* str) ^ (hash> 5); <br/>}< br/> return hash; <br/>}< br/>/* End Of AP Hash Function */