hash algorithms

hash_algo.c

//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;
}