10个经典的字符串hash函数的C代码实现
2011-08-30 11:48
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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 */
转贴:http://www.cppblog.com/xosen/archive/2009/10/21/99089.aspx
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几种经典的Hash算法的实现(源代码)
●PHP中出现的字符串Hash函数
static unsigned long hashpjw(char *arKey, unsigned int nKeyLength) { unsigned long h = 0, g; char *arEnd=arKey+nKeyLength; while (arKey < arEnd) { h = (h << 4) + *arKey++; if ((g = (h & 0xF0000000))) { h = h ^ (g >> 24); h = h ^ g; } } return h; }
●OpenSSL中出现的字符串Hash函数
unsigned long lh_strhash(char *str) { int i,l; unsigned long ret=0; unsigned short *s; if (str == NULL) return(0); l=(strlen(str)+1)/2; s=(unsigned short *)str; for (i=0; i ret^=(s[i]<<(i&0x0f)); return(ret); } /* The following hash seems to work very well on normal text strings * no collisions on /usr/dict/words and it distributes on %2^n quite * well, not as good as MD5, but still good. */ unsigned long lh_strhash(const char *c) { unsigned long ret=0; long n; unsigned long v; int r; if ((c == NULL) || (*c == '\0')) return(ret); /* unsigned char b[16]; MD5(c,strlen(c),b); return(b[0]|(b[1]<<8)|(b[2]<<16)|(b[3]<<24)); */ n=0x100; while (*c) { v=n|(*c); n+=0x100; r= (int)((v>>2)^v)&0x0f; ret=(ret(32-r)); ret&=0xFFFFFFFFL; ret^=v*v; c++; } return((ret>>16)^ret); }
●MySql中出现的字符串Hash函数
#ifndef NEW_HASH_FUNCTION /* Calc hashvalue for a key */ static uint calc_hashnr(const byte *key,uint length) { register uint nr=1, nr2=4; while (length--) { nr^= (((nr & 63)+nr2)*((uint) (uchar) *key++))+ (nr << 8); nr2+=3; } return((uint) nr); } /* Calc hashvalue for a key, case indepenently */ static uint calc_hashnr_caseup(const byte *key,uint length) { register uint nr=1, nr2=4; while (length--) { nr^= (((nr & 63)+nr2)*((uint) (uchar) toupper(*key++)))+ (nr << 8); nr2+=3; } return((uint) nr); } #else /* * Fowler/Noll/Vo hash * * The basis of the hash algorithm was taken from an idea sent by email to the * IEEE Posix P1003.2 mailing list from Phong Vo (kpv@research.att.com) and * Glenn Fowler (gsf@research.att.com). Landon Curt Noll (chongo@toad.com) * later improved on their algorithm. * * The magic is in the interesting relationship between the special prime * 16777619 (2^24 + 403) and 2^32 and 2^8. * * This hash produces the fewest collisions of any function that we've seen so * far, and works well on both numbers and strings. */ uint calc_hashnr(const byte *key, uint len) { const byte *end=key+len; uint hash; for (hash = 0; key < end; key++) { hash *= 16777619; hash ^= (uint) *(uchar*) key; } return (hash); } uint calc_hashnr_caseup(const byte *key, uint len) { const byte *end=key+len; uint hash; for (hash = 0; key < end; key++) { hash *= 16777619; hash ^= (uint) (uchar) toupper(*key); } return (hash); } #endif
Mysql中对字符串Hash函数还区分了大小写
●另一个经典字符串Hash函数
unsigned int hash(char *str) { register unsigned int h; register unsigned char *p; for(h=0, p = (unsigned char *)str; *p ; p++) h = 31 * h + *p; return h; }
转贴:http://blog.minidx.com/2008/01/27/446.html
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