通用字符串哈希函数

原文链接地址： http://www.partow.net/programming/hashfunctions/

 

这些字符串哈希函数都在工程中运用的很广，就是不知道具体的区别以及适用范围，不管怎么样，先添上代码，有空再仔细研究。

#include "GeneralHashFunctions.h" unsigned int RSHash(char* str, unsigned int len) { unsigned int b = 378551; unsigned int a = 63689; unsigned int hash = 0; unsigned int i = 0; for(i = 0; i < len; str++, i++) { hash = hash * a + (*str); a = a * b; } return hash; } /* End Of RS Hash Function */ unsigned int JSHash(char* str, unsigned int len) { unsigned int hash = 1315423911; unsigned int i = 0; for(i = 0; i < len; str++, i++) { hash ^= ((hash << 5) + (*str) + (hash >> 2)); } return hash; } /* End Of JS Hash Function */ 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; unsigned int i = 0; for(i = 0; i < len; str++, i++) { hash = (hash << OneEighth) + (*str); if((test = hash & HighBits) != 0) { hash = (( hash ^ (test >> ThreeQuarters)) & (~HighBits)); } } return hash; } /* End Of P. J. Weinberger Hash Function */ unsigned int ELFHash(char* str, unsigned int len) { unsigned int hash = 0; unsigned int x = 0; unsigned int i = 0; for(i = 0; i < len; str++, i++) { hash = (hash << 4) + (*str); if((x = hash & 0xF0000000L) != 0) { hash ^= (x >> 24); } hash &= ~x; } return hash; } /* End Of ELF Hash Function */ unsigned int BKDRHash(char* str, unsigned int len) { unsigned int seed = 131; /* 31 131 1313 13131 131313 etc.. */ unsigned int hash = 0; unsigned int i = 0; for(i = 0; i < len; str++, i++) { hash = (hash * seed) + (*str); } return hash; } /* End Of BKDR Hash Function */ unsigned int SDBMHash(char* str, unsigned int len) { unsigned int hash = 0; unsigned int i = 0; for(i = 0; i < len; str++, i++) { hash = (*str) + (hash << 6) + (hash << 16) - hash; } return hash; } /* End Of SDBM Hash Function */ unsigned int DJBHash(char* str, unsigned int len) { unsigned int hash = 5381; unsigned int i = 0; for(i = 0; i < len; str++, i++) { hash = ((hash << 5) + hash) + (*str); } return hash; } /* End Of DJB Hash Function */ unsigned int DEKHash(char* str, unsigned int len) { unsigned int hash = len; unsigned int i = 0; for(i = 0; i < len; str++, i++) { hash = ((hash << 5) ^ (hash >> 27)) ^ (*str); } return hash; } /* End Of DEK Hash Function */ unsigned int BPHash(char* str, unsigned int len) { unsigned int hash = 0; unsigned int i = 0; for(i = 0; i < len; str++, i++) { hash = hash << 7 ^ (*str); } return hash; } /* End Of BP Hash Function */ unsigned int FNVHash(char* str, unsigned int len) { const unsigned int fnv_prime = 0x811C9DC5; unsigned int hash = 0; unsigned int i = 0; for(i = 0; i < len; str++, i++) { hash *= fnv_prime; hash ^= (*str); } return hash; } /* End Of FNV Hash Function */ unsigned int APHash(char* str, unsigned int len) { unsigned int hash = 0xAAAAAAAA; unsigned int i = 0; for(i = 0; i < len; str++, i++) { hash ^= ((i & 1) == 0) ? ( (hash << 7) ^ (*str) * (hash >> 3)) : (~((hash << 11) + ((*str) ^ (hash >> 5)))); } return hash; } /* End Of AP Hash Function */