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The new jhash implementation

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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However, lookup2() is outdated as Bob wrote a new hash function called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 2010-12-03 02:39:01 +00:00 committed by David S. Miller
parent 68835aba4d
commit 60d509c823
1 changed files with 105 additions and 78 deletions
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183
include/linux/jhash.h
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@ -3,129 +3,156 @@
/* jhash.h: Jenkins hash support.
*
* Copyright (C) 1996 Bob Jenkins (bob_jenkins@burtleburtle.net)
* Copyright (C) 2006. Bob Jenkins (bob_jenkins@burtleburtle.net)
*
* http://burtleburtle.net/bob/hash/
*
* These are the credits from Bob's sources:
*
* lookup2.c, by Bob Jenkins, December 1996, Public Domain.
* hash(), hash2(), hash3, and mix() are externally useful functions.
* Routines to test the hash are included if SELF_TEST is defined.
* You can use this free for any purpose. It has no warranty.
* lookup3.c, by Bob Jenkins, May 2006, Public Domain.
*
* Copyright (C) 2003 David S. Miller (davem@redhat.com)
* These are functions for producing 32-bit hashes for hash table lookup.
* hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final()
* are externally useful functions. Routines to test the hash are included
* if SELF_TEST is defined. You can use this free for any purpose. It's in
* the public domain. It has no warranty.
*
* Copyright (C) 2009-2010 Jozsef Kadlecsik (kadlec@blackhole.kfki.hu)
*
* I've modified Bob's hash to be useful in the Linux kernel, and
* any bugs present are surely my fault. -DaveM
* any bugs present are my fault.
* Jozsef
*/
#include <linux/bitops.h>
#include <linux/unaligned/packed_struct.h>
/* NOTE: Arguments are modified. */
#define __jhash_mix(a, b, c) \
{ \
a -= b; a -= c; a ^= (c>>13); \
b -= c; b -= a; b ^= (a<<8); \
c -= a; c -= b; c ^= (b>>13); \
a -= b; a -= c; a ^= (c>>12); \
b -= c; b -= a; b ^= (a<<16); \
c -= a; c -= b; c ^= (b>>5); \
a -= b; a -= c; a ^= (c>>3); \
b -= c; b -= a; b ^= (a<<10); \
c -= a; c -= b; c ^= (b>>15); \
/* Best hash sizes are of power of two */
#define jhash_size(n) ((u32)1<<(n))
/* Mask the hash value, i.e (value & jhash_mask(n)) instead of (value % n) */
#define jhash_mask(n) (jhash_size(n)-1)
/* __jhash_mix -- mix 3 32-bit values reversibly. */
#define __jhash_mix(a, b, c) \
{ \
a -= c; a ^= rol32(c, 4); c += b; \
b -= a; b ^= rol32(a, 6); a += c; \
c -= b; c ^= rol32(b, 8); b += a; \
a -= c; a ^= rol32(c, 16); c += b; \
b -= a; b ^= rol32(a, 19); a += c; \
c -= b; c ^= rol32(b, 4); b += a; \
}
/* The golden ration: an arbitrary value */
#define JHASH_GOLDEN_RATIO 0x9e3779b9
/* __jhash_final - final mixing of 3 32-bit values (a,b,c) into c */
#define __jhash_final(a, b, c) \
{ \
c ^= b; c -= rol32(b, 14); \
a ^= c; a -= rol32(c, 11); \
b ^= a; b -= rol32(a, 25); \
c ^= b; c -= rol32(b, 16); \
a ^= c; a -= rol32(c, 4); \
b ^= a; b -= rol32(a, 14); \
c ^= b; c -= rol32(b, 24); \
}
/* The most generic version, hashes an arbitrary sequence
* of bytes. No alignment or length assumptions are made about
* the input key.
/* An arbitrary initial parameter */
#define JHASH_INITVAL 0xdeadbeef
/* jhash - hash an arbitrary key
* @k: sequence of bytes as key
* @length: the length of the key
* @initval: the previous hash, or an arbitray value
*
* The generic version, hashes an arbitrary sequence of bytes.
* No alignment or length assumptions are made about the input key.
*
* Returns the hash value of the key. The result depends on endianness.
*/
static inline u32 jhash(const void *key, u32 length, u32 initval)
{
u32 a, b, c, len;
u32 a, b, c;
const u8 *k = key;
len = length;
a = b = JHASH_GOLDEN_RATIO;
c = initval;
while (len >= 12) {
a += (k[0] +((u32)k[1]<<8) +((u32)k[2]<<16) +((u32)k[3]<<24));
b += (k[4] +((u32)k[5]<<8) +((u32)k[6]<<16) +((u32)k[7]<<24));
c += (k[8] +((u32)k[9]<<8) +((u32)k[10]<<16)+((u32)k[11]<<24));
__jhash_mix(a,b,c);
/* Set up the internal state */
a = b = c = JHASH_INITVAL + length + initval;
/* All but the last block: affect some 32 bits of (a,b,c) */
while (length > 12) {
a += __get_unaligned_cpu32(k);
b += __get_unaligned_cpu32(k + 4);
c += __get_unaligned_cpu32(k + 8);
__jhash_mix(a, b, c);
length -= 12;
k += 12;
len -= 12;
}
c += length;
switch (len) {
case 11: c += ((u32)k[10]<<24);
case 10: c += ((u32)k[9]<<16);
case 9 : c += ((u32)k[8]<<8);
case 8 : b += ((u32)k[7]<<24);
case 7 : b += ((u32)k[6]<<16);
case 6 : b += ((u32)k[5]<<8);
case 5 : b += k[4];
case 4 : a += ((u32)k[3]<<24);
case 3 : a += ((u32)k[2]<<16);
case 2 : a += ((u32)k[1]<<8);
case 1 : a += k[0];
};
__jhash_mix(a,b,c);
/* Last block: affect all 32 bits of (c) */
/* All the case statements fall through */
switch (length) {
case 12: c += (u32)k[11]<<24;
case 11: c += (u32)k[10]<<16;
case 10: c += (u32)k[9]<<8;
case 9: c += k[8];
case 8: b += (u32)k[7]<<24;
case 7: b += (u32)k[6]<<16;
case 6: b += (u32)k[5]<<8;
case 5: b += k[4];
case 4: a += (u32)k[3]<<24;
case 3: a += (u32)k[2]<<16;
case 2: a += (u32)k[1]<<8;
case 1: a += k[0];
__jhash_final(a, b, c);
case 0: /* Nothing left to add */
break;
}
return c;
}
/* A special optimized version that handles 1 or more of u32s.
* The length parameter here is the number of u32s in the key.
/* jhash2 - hash an array of u32's
* @k: the key which must be an array of u32's
* @length: the number of u32's in the key
* @initval: the previous hash, or an arbitray value
*
* Returns the hash value of the key.
*/
static inline u32 jhash2(const u32 *k, u32 length, u32 initval)
{
u32 a, b, c, len;
u32 a, b, c;
a = b = JHASH_GOLDEN_RATIO;
c = initval;
len = length;
/* Set up the internal state */
a = b = c = JHASH_INITVAL + (length<<2) + initval;
while (len >= 3) {
/* Handle most of the key */
while (length > 3) {
a += k[0];
b += k[1];
c += k[2];
__jhash_mix(a, b, c);
k += 3; len -= 3;
length -= 3;
k += 3;
}
c += length * 4;
switch (len) {
case 2 : b += k[1];
case 1 : a += k[0];
};
__jhash_mix(a,b,c);
/* Handle the last 3 u32's: all the case statements fall through */
switch (length) {
case 3: c += k[2];
case 2: b += k[1];
case 1: a += k[0];
__jhash_final(a, b, c);
case 0: /* Nothing left to add */
break;
}
return c;
}
/* A special ultra-optimized versions that knows they are hashing exactly
* 3, 2 or 1 word(s).
*
* NOTE: In particular the "c += length; __jhash_mix(a,b,c);" normally
* done at the end is not done here.
*/
/* jhash_3words - hash exactly 3, 2 or 1 word(s) */
static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
{
a += JHASH_GOLDEN_RATIO;
b += JHASH_GOLDEN_RATIO;
a += JHASH_INITVAL;
b += JHASH_INITVAL;
c += initval;
__jhash_mix(a, b, c);
__jhash_final(a, b, c);
return c;
}