The new jhash implementation
The current jhash.h implements the lookup2() hash function by Bob Jenkins. However, lookup2() is outdated as Bob wrote a new hash function called lookup3(). The patch replaces the lookup2() implementation of the 'jhash*' functions with that of lookup3(). You can read a longer comparison of the two and other hash functions at http://burtleburtle.net/bob/hash/doobs.html. Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu> Acked-by: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jozsef Kadlecsik
David S. Miller
Родитель
68835aba4d
Коммит
60d509c823
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@ -3,129 +3,156 @@
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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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* Copyright (C) 2006. 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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* lookup3.c, by Bob Jenkins, May 2006, Public Domain.
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*
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* Copyright (C) 2003 David S. Miller (davem@redhat.com)
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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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* Copyright (C) 2009-2010 Jozsef Kadlecsik (kadlec@blackhole.kfki.hu)
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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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* any bugs present are my fault.
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* Jozsef
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*/
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#include <linux/bitops.h>
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#include <linux/unaligned/packed_struct.h>
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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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/* Best hash sizes are of power of two */
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#define jhash_size(n) ((u32)1<<(n))
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/* Mask the hash value, i.e (value & jhash_mask(n)) instead of (value % n) */
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#define jhash_mask(n) (jhash_size(n)-1)
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/* __jhash_mix -- mix 3 32-bit values reversibly. */
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#define __jhash_mix(a, b, c) \
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{ \
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a -= c; a ^= rol32(c, 4); c += b; \
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b -= a; b ^= rol32(a, 6); a += c; \
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c -= b; c ^= rol32(b, 8); b += a; \
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a -= c; a ^= rol32(c, 16); c += b; \
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b -= a; b ^= rol32(a, 19); a += c; \
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c -= b; c ^= rol32(b, 4); b += a; \
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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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/* __jhash_final - final mixing of 3 32-bit values (a,b,c) into c */
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#define __jhash_final(a, b, c) \
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{ \
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c ^= b; c -= rol32(b, 14); \
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a ^= c; a -= rol32(c, 11); \
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b ^= a; b -= rol32(a, 25); \
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c ^= b; c -= rol32(b, 16); \
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a ^= c; a -= rol32(c, 4); \
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b ^= a; b -= rol32(a, 14); \
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c ^= b; c -= rol32(b, 24); \
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}
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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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/* An arbitrary initial parameter */
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#define JHASH_INITVAL 0xdeadbeef
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/* jhash - hash an arbitrary key
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* @k: sequence of bytes as key
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* @length: the length of the key
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* @initval: the previous hash, or an arbitray value
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*
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* The generic version, hashes an arbitrary sequence of bytes.
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* No alignment or length assumptions are made about the input key.
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*
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* Returns the hash value of the key. The result depends on endianness.
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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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u32 a, b, c;
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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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/* Set up the internal state */
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a = b = c = JHASH_INITVAL + length + initval;
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/* All but the last block: affect some 32 bits of (a,b,c) */
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while (length > 12) {
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a += __get_unaligned_cpu32(k);
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b += __get_unaligned_cpu32(k + 4);
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c += __get_unaligned_cpu32(k + 8);
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__jhash_mix(a, b, c);
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length -= 12;
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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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/* Last block: affect all 32 bits of (c) */
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/* All the case statements fall through */
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switch (length) {
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case 12: c += (u32)k[11]<<24;
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case 11: c += (u32)k[10]<<16;
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case 10: c += (u32)k[9]<<8;
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case 9: c += k[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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__jhash_final(a, b, c);
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case 0: /* Nothing left to add */
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break;
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}
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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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/* jhash2 - hash an array of u32's
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* @k: the key which must be an array of u32's
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* @length: the number of u32's in the key
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* @initval: the previous hash, or an arbitray value
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*
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* Returns the hash value of 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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u32 a, b, c;
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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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/* Set up the internal state */
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a = b = c = JHASH_INITVAL + (length<<2) + initval;
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while (len >= 3) {
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/* Handle most of the key */
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while (length > 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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length -= 3;
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k += 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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/* Handle the last 3 u32's: all the case statements fall through */
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switch (length) {
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case 3: c += k[2];
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case 2: b += k[1];
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case 1: a += k[0];
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__jhash_final(a, b, c);
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case 0: /* Nothing left to add */
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break;
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}
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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 particular 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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/* jhash_3words - hash exactly 3, 2 or 1 word(s) */
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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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a += JHASH_INITVAL;
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b += JHASH_INITVAL;
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c += initval;
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__jhash_mix(a, b, c);
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__jhash_final(a, b, c);
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return c;
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}
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