Commit 60d509c8 authored by Jozsef Kadlecsik's avatar Jozsef Kadlecsik Committed by David S. Miller

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However, lookup2() is outdated as Bob wrote a new hash function called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: default avatarJozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Acked-by: default avatarRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 68835aba
......@@ -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>
/* 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)
/* NOTE: Arguments are modified. */
/* __jhash_mix -- mix 3 32-bit values reversibly. */
#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); \
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; \
}
/* __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 golden ration: an arbitrary value */
#define JHASH_GOLDEN_RATIO 0x9e3779b9
/* An arbitrary initial parameter */
#define JHASH_INITVAL 0xdeadbeef
/* The most generic version, hashes an arbitrary sequence
* of bytes. No alignment or length assumptions are made about
* the input key.
/* 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;
}
......
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