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Message-Id: <1291379941-31565-3-git-send-email-kadlec@blackhole.kfki.hu>
Date: Fri, 3 Dec 2010 13:39:01 +0100
From: Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>
To: linux-kernel@...r.kernel.org
Cc: netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
Linus Torvalds <torvalds@...l.org>,
Rusty Russell <rusty@...tcorp.com.au>,
Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>
Subject: [PATCH 2/2] 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However, lookup2() is outdated as Bob wrote a new hash function called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.
---
include/linux/jhash.h | 183 ++++++++++++++++++++++++++++---------------------
1 files changed, 105 insertions(+), 78 deletions(-)
diff --git a/include/linux/jhash.h b/include/linux/jhash.h
index ced1159..47cb09e 100644
--- a/include/linux/jhash.h
+++ b/include/linux/jhash.h
@@ -3,129 +3,156 @@
/* jhash.h: Jenkins hash support.
*
- * Copyright (C) 1996 Bob Jenkins (bob_jenkins@...tleburtle.net)
+ * Copyright (C) 2006. Bob Jenkins (bob_jenkins@...tleburtle.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@...hat.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@...ckhole.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)
+
+/* __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; \
+}
-/* 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); \
+/* __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;
}
--
1.7.0.4
--
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