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 However, lookup2() is outdated as Bob wrote a new hash function called lookup3().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 new hash function - mixes better than lookup2(): it passes the check that every input bit changes every output bit 50% of the time, while lookup2() failed it. - performs better: compiled with -O2 on Core2 Duo, lookup3() 20-40% faster than lookup2() depending on the key length. 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@xxxxxxxxxxxxxxxxx> --- include/linux/jhash.h | 136 +++----------------------------------------- lib/Makefile | 2 +- lib/jhash.c | 153 +++++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 162 insertions(+), 129 deletions(-) create mode 100644 lib/jhash.c diff --git a/include/linux/jhash.h b/include/linux/jhash.h index ced1159..ca69ac3 100644 --- a/include/linux/jhash.h +++ b/include/linux/jhash.h @@ -1,134 +1,14 @@ #ifndef _LINUX_JHASH_H #define _LINUX_JHASH_H -/* jhash.h: Jenkins hash support. - * - * Copyright (C) 1996 Bob Jenkins (bob_jenkins@xxxxxxxxxxxxxxxx) - * - * 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. - * - * Copyright (C) 2003 David S. Miller (davem@xxxxxxxxxx) - * - * I've modified Bob's hash to be useful in the Linux kernel, and - * any bugs present are surely my fault. -DaveM - */ - -/* 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); \ -} - -/* The golden ration: an arbitrary value */ -#define JHASH_GOLDEN_RATIO 0x9e3779b9 - -/* The most generic version, hashes an arbitrary sequence - * of bytes. No alignment or length assumptions are made about - * the input key. - */ -static inline u32 jhash(const void *key, u32 length, u32 initval) -{ - u32 a, b, c, len; - 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); - - 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); - - 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. - */ -static inline u32 jhash2(const u32 *k, u32 length, u32 initval) -{ - u32 a, b, c, len; - - a = b = JHASH_GOLDEN_RATIO; - c = initval; - len = length; - - while (len >= 3) { - a += k[0]; - b += k[1]; - c += k[2]; - __jhash_mix(a, b, c); - k += 3; len -= 3; - } - - c += length * 4; - - switch (len) { - case 2 : b += k[1]; - case 1 : a += k[0]; - }; - - __jhash_mix(a,b,c); - - 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. - */ -static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval) -{ - a += JHASH_GOLDEN_RATIO; - b += JHASH_GOLDEN_RATIO; - c += initval; - - __jhash_mix(a, b, c); - - return c; -} +/* 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) + +extern u32 jhash(const void *key, u32 length, u32 initval); +extern u32 jhash2(const u32 *k, u32 length, u32 initval); +extern u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval); static inline u32 jhash_2words(u32 a, u32 b, u32 initval) { diff --git a/lib/Makefile b/lib/Makefile index e6a3763..a1a4932 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -10,7 +10,7 @@ endif lib-y := ctype.o string.o vsprintf.o cmdline.o \ rbtree.o radix-tree.o dump_stack.o \ idr.o int_sqrt.o extable.o prio_tree.o \ - sha1.o irq_regs.o reciprocal_div.o argv_split.o \ + jhash.o sha1.o irq_regs.o reciprocal_div.o argv_split.o \ proportions.o prio_heap.o ratelimit.o show_mem.o \ is_single_threaded.o plist.o decompress.o flex_array.o diff --git a/lib/jhash.c b/lib/jhash.c new file mode 100644 index 0000000..593cc77 --- /dev/null +++ b/lib/jhash.c @@ -0,0 +1,153 @@ +/* jhash.c: Jenkins hash support. + * + * Copyright (C) 2006. Bob Jenkins (bob_jenkins@xxxxxxxxxxxxxxxx) + * + * http://burtleburtle.net/bob/hash/ + * + * These are the credits from Bob's sources: + * + * lookup3.c, by Bob Jenkins, May 2006, Public Domain. + * + * 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@xxxxxxxxxxxxxxxxx) + * + * I've modified Bob's hash to be useful in the Linux kernel, and + * any bugs present are my fault. + * Jozsef + */ +#include <linux/bitops.h> +#include <linux/module.h> +#include <linux/jhash.h> + +/* __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; \ +} + +/* __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); \ +} + +/* 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. + */ +u32 jhash(const void *key, u32 length, u32 initval) +{ + u32 a, b, c; + const u8 *k = key; + + /* 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 += 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); + length -= 12; + k += 12; + } + /* 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; +} +EXPORT_SYMBOL(jhash); + +/* 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. + */ +u32 jhash2(const u32 *k, u32 length, u32 initval) +{ + u32 a, b, c; + + /* Set up the internal state */ + a = b = c = JHASH_INITVAL + (length<<2) + initval; + + /* Handle most of the key */ + while (length > 3) { + a += k[0]; + b += k[1]; + c += k[2]; + __jhash_mix(a, b, c); + length -= 3; + k += 3; + } + + /* 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; +} +EXPORT_SYMBOL(jhash2); + +/* jhash_3words - hash exactly 3, 2 or 1 word(s) */ +u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval) +{ + a += JHASH_INITVAL; + b += JHASH_INITVAL; + c += initval; + + __jhash_mix(a, b, c); + + return c; +} +EXPORT_SYMBOL(jhash_3words); -- 1.7.0.4 -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
