144 строки
3.2 KiB
C
144 строки
3.2 KiB
C
#ifndef _LINUX_JHASH_H
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#define _LINUX_JHASH_H
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/* jhash.h: Jenkins hash support.
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*
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* Copyright (C) 1996 Bob Jenkins (bob_jenkins@burtleburtle.net)
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*
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* http://burtleburtle.net/bob/hash/
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*
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* These are the credits from Bob's sources:
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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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*
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* Copyright (C) 2003 David S. Miller (davem@redhat.com)
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*
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* I've modified Bob's hash to be useful in the Linux kernel, and
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* any bugs present are surely my fault. -DaveM
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*/
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/* NOTE: Arguments are modified. */
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#define __jhash_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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/* The golden ration: an arbitrary value */
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#define JHASH_GOLDEN_RATIO 0x9e3779b9
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/* The most generic version, hashes an arbitrary sequence
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* of bytes. No alignment or length assumptions are made about
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* the input key.
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*/
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static inline u32 jhash(const void *key, u32 length, u32 initval)
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{
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u32 a, b, c, len;
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const u8 *k = key;
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len = length;
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a = b = JHASH_GOLDEN_RATIO;
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c = initval;
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while (len >= 12) {
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a += (k[0] +((u32)k[1]<<8) +((u32)k[2]<<16) +((u32)k[3]<<24));
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b += (k[4] +((u32)k[5]<<8) +((u32)k[6]<<16) +((u32)k[7]<<24));
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c += (k[8] +((u32)k[9]<<8) +((u32)k[10]<<16)+((u32)k[11]<<24));
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__jhash_mix(a,b,c);
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k += 12;
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len -= 12;
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}
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c += length;
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switch (len) {
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case 11: c += ((u32)k[10]<<24);
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case 10: c += ((u32)k[9]<<16);
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case 9 : c += ((u32)k[8]<<8);
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case 8 : b += ((u32)k[7]<<24);
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case 7 : b += ((u32)k[6]<<16);
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case 6 : b += ((u32)k[5]<<8);
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case 5 : b += k[4];
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case 4 : a += ((u32)k[3]<<24);
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case 3 : a += ((u32)k[2]<<16);
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case 2 : a += ((u32)k[1]<<8);
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case 1 : a += k[0];
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};
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__jhash_mix(a,b,c);
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return c;
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}
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/* A special optimized version that handles 1 or more of u32s.
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* The length parameter here is the number of u32s in the key.
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*/
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static inline u32 jhash2(const u32 *k, u32 length, u32 initval)
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{
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u32 a, b, c, len;
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a = b = JHASH_GOLDEN_RATIO;
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c = initval;
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len = length;
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while (len >= 3) {
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a += k[0];
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b += k[1];
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c += k[2];
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__jhash_mix(a, b, c);
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k += 3; len -= 3;
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}
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c += length * 4;
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switch (len) {
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case 2 : b += k[1];
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case 1 : a += k[0];
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};
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__jhash_mix(a,b,c);
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return c;
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}
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/* A special ultra-optimized versions that knows they are hashing exactly
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* 3, 2 or 1 word(s).
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*
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* NOTE: In partilar the "c += length; __jhash_mix(a,b,c);" normally
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* done at the end is not done here.
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*/
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static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
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{
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a += JHASH_GOLDEN_RATIO;
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b += JHASH_GOLDEN_RATIO;
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c += initval;
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__jhash_mix(a, b, c);
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return c;
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}
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static inline u32 jhash_2words(u32 a, u32 b, u32 initval)
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{
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return jhash_3words(a, b, 0, initval);
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}
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static inline u32 jhash_1word(u32 a, u32 initval)
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{
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return jhash_3words(a, 0, 0, initval);
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}
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#endif /* _LINUX_JHASH_H */
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