81 lines
2.5 KiB
C
Executable File
81 lines
2.5 KiB
C
Executable File
/*
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* Hash lookup function.
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* Copyright (C) 2003, 2004 Mondru AB.
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*
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* The contents of this file may be used under the terms of the GNU
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* General Public License Version 2, provided that the above copyright
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* notice and this permission notice is included in all copies or
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* substantial portions of the software.
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*
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*/
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/**
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* lookup()
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* Generates a 32 bit hash.
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* Based on public domain code by Bob Jenkins
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* It should be one of the best hash functions around in terms of both
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* statistical properties and speed. It is NOT recommended for cryptographic
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* purposes.
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**/
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unsigned long int lookup( k, length, level)
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register unsigned char *k; /* the key */
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register unsigned long int length; /* the length of the key */
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register unsigned long int level; /* the previous hash, or an arbitrary value*/
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{
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#define mix(a,b,c) \
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{ \
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a -= b; a -= c; a ^= (c>>13); \
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b -= c; b -= a; b ^= (a<<8); \
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c -= a; c -= b; c ^= (b>>13); \
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a -= b; a -= c; a ^= (c>>12); \
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b -= c; b -= a; b ^= (a<<16); \
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c -= a; c -= b; c ^= (b>>5); \
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a -= b; a -= c; a ^= (c>>3); \
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b -= c; b -= a; b ^= (a<<10); \
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c -= a; c -= b; c ^= (b>>15); \
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}
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typedef unsigned long int ub4; /* unsigned 4-byte quantities */
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typedef unsigned char ub1; /* unsigned 1-byte quantities */
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register unsigned long int a,b,c,len;
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/* Set up the internal state */
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len = length;
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a = b = 0x9e3779b9; /* the golden ratio; an arbitrary value */
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c = level; /* the previous hash value */
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/*---------------------------------------- handle most of the key */
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while (len >= 12)
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{
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a += (k[0] +((ub4)k[1]<<8) +((ub4)k[2]<<16) +((ub4)k[3]<<24));
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b += (k[4] +((ub4)k[5]<<8) +((ub4)k[6]<<16) +((ub4)k[7]<<24));
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c += (k[8] +((ub4)k[9]<<8) +((ub4)k[10]<<16)+((ub4)k[11]<<24));
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mix(a,b,c);
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k += 12; len -= 12;
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}
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/*------------------------------------- handle the last 11 bytes */
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c += length;
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switch(len) /* all the case statements fall through */
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{
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case 11: c+=((ub4)k[10]<<24);
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case 10: c+=((ub4)k[9]<<16);
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case 9 : c+=((ub4)k[8]<<8);
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/* the first byte of c is reserved for the length */
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case 8 : b+=((ub4)k[7]<<24);
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case 7 : b+=((ub4)k[6]<<16);
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case 6 : b+=((ub4)k[5]<<8);
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case 5 : b+=k[4];
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case 4 : a+=((ub4)k[3]<<24);
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case 3 : a+=((ub4)k[2]<<16);
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case 2 : a+=((ub4)k[1]<<8);
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case 1 : a+=k[0];
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/* case 0: nothing left to add */
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}
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mix(a,b,c);
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/*-------------------------------------------- report the result */
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return c;
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}
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