92 lines
2.4 KiB
C
Executable File
92 lines
2.4 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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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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a += (k[0] + ((ub4) k[1] << 8) + ((ub4) k[2] << 16) +
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((ub4) k[3] << 24));
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b += (k[4] + ((ub4) k[5] << 8) + ((ub4) k[6] << 16) +
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((ub4) k[7] << 24));
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c += (k[8] + ((ub4) k[9] << 8) + ((ub4) k[10] << 16) +
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((ub4) k[11] << 24));
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mix(a, b, c);
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k += 12;
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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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case 11:
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c += ((ub4) k[10] << 24);
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case 10:
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c += ((ub4) k[9] << 16);
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case 9:
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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:
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b += ((ub4) k[7] << 24);
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case 7:
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b += ((ub4) k[6] << 16);
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case 6:
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b += ((ub4) k[5] << 8);
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case 5:
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b += k[4];
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case 4:
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a += ((ub4) k[3] << 24);
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case 3:
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a += ((ub4) k[2] << 16);
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case 2:
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a += ((ub4) k[1] << 8);
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case 1:
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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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