几个常见的字符串HASH

      最近在看开源代码中遇到一些HASH处理字符串的问题，也搜索了些资料，摘录如下：

      PHP中出现过的HASH

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HASH

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; iret^=(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中出现过的HASH

#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 ([e-mail]) and* Glenn Fowler ([e-mail]). Landon Curt Noll ([e-mail])* 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

      排版有点乱，未来得及整理。

最近看cocos-2dx代码，也使用类似的hash来计算字符串的信息码：

static inline unsigned int getHashCodeByString(const char *key){unsigned int len = strlen(key);const char *end=key+len;unsigned int hash;for (hash = 0; key < end; key++){hash *= 16777619;hash ^= (unsigned int) (unsigned char) toupper(*key);}return (hash);}