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// $Id: hash.cpp 400 2006-07-31 02:46:59Z hieuhoang1972 $
#define mix(a,b,c) \
{ \
a -= b; a -= c; a ^= (c>>13); \
b -= c; b -= a; b ^= (a<<8); \
c -= a; c -= b; c ^= (b>>13); \
a -= b; a -= c; a ^= (c>>12); \
b -= c; b -= a; b ^= (a<<16); \
c -= a; c -= b; c ^= (b>>5); \
a -= b; a -= c; a ^= (c>>3); \
b -= c; b -= a; b ^= (a<<10); \
c -= a; c -= b; c ^= (b>>15); \
}
/* the key */
/* the length of the key */
/* the previous hash, or an arbitrary value */
unsigned int quick_hash(register const char *k, register unsigned int length, register unsigned int initval)
{
register unsigned int a,b,c,len;
/* Set up the internal state */
len = length;
a = b = 0x9e3779b9; /* the golden ratio; an arbitrary value */
c = initval; /* the previous hash value */
/*---------------------------------------- handle most of the key */
while (len >= 12)
{
a += (k[0] +((unsigned int)k[1]<<8) +((unsigned int)k[2]<<16) +((unsigned int)k[3]<<24));
b += (k[4] +((unsigned int)k[5]<<8) +((unsigned int)k[6]<<16) +((unsigned int)k[7]<<24));
c += (k[8] +((unsigned int)k[9]<<8) +((unsigned int)k[10]<<16)+((unsigned int)k[11]<<24));
mix(a,b,c);
k += 12; len -= 12;
}
/*------------------------------------- handle the last 11 bytes */
c += length;
switch(len) /* all the case statements fall through */
{
case 11: c+=((unsigned int)k[10]<<24);
case 10: c+=((unsigned int)k[9]<<16);
case 9 : c+=((unsigned int)k[8]<<8);
/* the first byte of c is reserved for the length */
case 8 : b+=((unsigned int)k[7]<<24);
case 7 : b+=((unsigned int)k[6]<<16);
case 6 : b+=((unsigned int)k[5]<<8);
case 5 : b+=k[4];
case 4 : a+=((unsigned int)k[3]<<24);
case 3 : a+=((unsigned int)k[2]<<16);
case 2 : a+=((unsigned int)k[1]<<8);
case 1 : a+=k[0];
/* case 0: nothing left to add */
}
mix(a,b,c);
/*-------------------------------------------- report the result */
return c;
}
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