hash: use more recent lookup3 algorithm instead of lookup2
Bob Jenkins published a newer hash function in May 2006, it has better distribution. See http://burtleburtle.net/bob/hash/doobs.html for lengthy comparisions.
This commit is contained in:
Florian Westphal
parent
7f8d0ea5a3
commit
1765f0ae0b
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@ -26,8 +26,7 @@
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#include "exp.h"
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#include "hash.h"
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static UINT32 jenkins_hash PARAMS((register UINT8 *k, register UINT32 length,
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register UINT32 initval));
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static UINT32 jenkins_hash PARAMS((UINT8 *k, UINT32 length, UINT32 initval));
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/**
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* Calculate hash value for a given string.
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@ -46,66 +45,74 @@ Hash( const char *String )
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} /* Hash */
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/*
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* This hash function originates from lookup2.c of Bob Jenkins
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* (URL: <http://burtleburtle.net/bob/c/lookup2.c>):
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* This hash function originates from lookup3.c of Bob Jenkins
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* (URL: <http://burtleburtle.net/bob/c/lookup3.c>):
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* --------------------------------------------------------------------
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* lookup2.c, by Bob Jenkins, December 1996, Public Domain.
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* hash(), hash2(), hash3, and mix() are externally useful functions.
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* Routines to test the hash are included if SELF_TEST is defined.
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* You can use this free for any purpose. It has no warranty.
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* lookup3.c, by Bob Jenkins, May 2006, Public Domain.
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* These are functions for producing 32-bit hashes for hash table lookup.
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* hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final()
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* are externally useful functions. Routines to test the hash are included
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* if SELF_TEST is defined. You can use this free for any purpose. It's in
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* the public domain. It has no warranty.
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* --------------------------------------------------------------------
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* Not all of his functions are used here.
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*/
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#define hashsize(n) ((UINT32)1<<(n))
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#define hashsize(n) ((uint32_t)1<<(n))
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#define hashmask(n) (hashsize(n)-1)
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#define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
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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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a -= c; a ^= rot(c, 4); c += b; \
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b -= a; b ^= rot(a, 6); a += c; \
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c -= b; c ^= rot(b, 8); b += a; \
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a -= c; a ^= rot(c,16); c += b; \
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b -= a; b ^= rot(a,19); a += c; \
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c -= b; c ^= rot(b, 4); b += a; \
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} /* mix */
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#define final(a,b,c) \
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{ \
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c ^= b; c -= rot(b,14); \
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a ^= c; a -= rot(c,11); \
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b ^= a; b -= rot(a,25); \
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c ^= b; c -= rot(b,16); \
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a ^= c; a -= rot(c,4); \
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b ^= a; b -= rot(a,14); \
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c ^= b; c -= rot(b,24); \
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}
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static UINT32
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jenkins_hash( register UINT8 *k, register UINT32 length, register UINT32 initval )
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jenkins_hash(UINT8 *k, UINT32 length, UINT32 initval)
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{
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/* k: the key
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* length: length of the key
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* initval: the previous hash, or an arbitrary value
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*/
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register UINT32 a,b,c,len;
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UINT32 a,b,c;
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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 = initval; /* the previous hash value */
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a = b = c = 0xdeadbeef + length + initval;
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/* handle most of the key */
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while (len >= 12)
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{
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while (length > 12) {
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a += (k[0] +((UINT32)k[1]<<8) +((UINT32)k[2]<<16) +((UINT32)k[3]<<24));
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b += (k[4] +((UINT32)k[5]<<8) +((UINT32)k[6]<<16) +((UINT32)k[7]<<24));
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c += (k[8] +((UINT32)k[9]<<8) +((UINT32)k[10]<<16)+((UINT32)k[11]<<24));
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mix(a,b,c);
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k += 12; len -= 12;
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length -= 12;
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k += 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( (int)len ) /* all the case statements fall through */
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/*-------------------------------- last block: affect all 32 bits of (c) */
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switch(length) /* all the case statements fall through */
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{
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case 11: c+=((UINT32)k[10]<<24);
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case 10: c+=((UINT32)k[9]<<16);
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case 9 : c+=((UINT32)k[8]<<8);
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/* the first byte of c is reserved for the length */
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case 12: c+=((UINT32)k[11])<<24;
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case 11: c+=((UINT32)k[10]<<16);
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case 10: c+=((UINT32)k[9]<<8);
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case 9 : c+=k[8];
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case 8 : b+=((UINT32)k[7]<<24);
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case 7 : b+=((UINT32)k[6]<<16);
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case 6 : b+=((UINT32)k[5]<<8);
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@ -114,11 +121,10 @@ jenkins_hash( register UINT8 *k, register UINT32 length, register UINT32 initval
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case 3 : a+=((UINT32)k[2]<<16);
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case 2 : a+=((UINT32)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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break;
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case 0 : return c;
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}
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mix(a,b,c);
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/* report the result */
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final(a,b,c);
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return c;
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} /* jenkins_hash */
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