On Tue, 10 Feb 2009, Scott Feldman wrote: > Jozsef Kadlecsik wrote: > > The patch replaces the lookup2() implementation of the 'jhash*' functions > > with that of lookup3(). > > Should the lookup3() be added to rather than replacing lookup2()? In case > some hardware vendor used the lookup2() version for weird things like flow > classification. Do you imagine a case where a system with lookup3() communicates with another one with lookup2() and they want to exchange data identified by the hash keys? But the normal approach is to use a random seed (initval), so even two systems with lookup2() won't generate the same hash value for the same key. Grepping through the whole kernel, at a lot of places jhash used with zero initval. :-(. Sure, it's safer to add a new header file instead, see below. > > /* The golden ration: an arbitrary value */ > > -#define JHASH_GOLDEN_RATIO 0x9e3779b9 > > +#define JHASH_GOLDEN_RATIO 0xdeadbeef > > The #define seems mis-named now. It's the new arbitrary value, taken from the original source :-). ---- 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 However, lookup2() is outdated as Bob wrote a new hash function called lookup3().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 adds jhash3.h which implements the lookup3() function(s) for the Linux kernel. Signed-off-by: Jozsef Kadlecsik <kadlec@xxxxxxxxxxxxxxxxx> --- include/linux/jhash3.h | 157 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 157 insertions(+), 0 deletions(-) create mode 100644 include/linux/jhash3.h diff --git a/include/linux/jhash3.h b/include/linux/jhash3.h new file mode 100644 index 0000000..99a203d --- /dev/null +++ b/include/linux/jhash3.h @@ -0,0 +1,157 @@ +#ifndef _LINUX_JHASH3_H +#define _LINUX_JHASH3_H + +/* jhash3.h: 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 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 + */ + +#define __rot(x,k) (((x)<<(k)) | ((x)>>(32-(k)))) + +/* __jhash3_mix - mix 3 32-bit values reversibly. */ +#define __jhash3_mix(a,b,c) \ +{ \ + a -= c; a ^= __rot(c, 4); c += b; \ + b -= a; b ^= __rot(a, 6); a += c; \ + c -= b; c ^= __rot(b, 8); b += a; \ + a -= c; a ^= __rot(c,16); c += b; \ + b -= a; b ^= __rot(a,19); a += c; \ + c -= b; c ^= __rot(b, 4); b += a; \ +} + +/* __jhash3_final - final mixing of 3 32-bit values (a,b,c) into c */ +#define __jhash3_final(a,b,c) \ +{ \ + c ^= b; c -= __rot(b,14); \ + a ^= c; a -= __rot(c,11); \ + b ^= a; b -= __rot(a,25); \ + c ^= b; c -= __rot(b,16); \ + a ^= c; a -= __rot(c,4); \ + b ^= a; b -= __rot(a,14); \ + c ^= b; c -= __rot(b,24); \ +} + +/* The golden ration: an arbitrary value */ +#define JHASH3_GOLDEN_RATIO 0xdeadbeef + +/* The most generic version, hashes an arbitrary sequence + * of bytes. No alignment or length assumptions are made about + * the input key. The result depends on endianness. + */ +static inline u32 jhash3(const void *key, u32 length, u32 initval) +{ + u32 a,b,c; + const u8 *k = key; + + /* Set up the internal state */ + a = b = c = JHASH3_GOLDEN_RATIO + 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)); + __jhash3_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]; + __jhash3_final(a, b, c); + case 0 : + 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. + */ +static inline u32 jhash3_words(const u32 *k, u32 length, u32 initval) +{ + u32 a, b, c; + + /* Set up the internal state */ + a = b = c = JHASH3_GOLDEN_RATIO + (length<<2) + initval; + + /* handle most of the key */ + while (length > 3) { + a += k[0]; + b += k[1]; + c += k[2]; + __jhash3_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]; + __jhash3_final(a, b, c); + case 0: /* 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). + */ +static inline u32 jhash3_3words(u32 a, u32 b, u32 c, u32 initval) +{ + a += JHASH3_GOLDEN_RATIO + initval; + b += JHASH3_GOLDEN_RATIO + initval; + c += JHASH3_GOLDEN_RATIO + initval; + + __jhash3_final(a, b, c); + + return c; +} + +static inline u32 jhash3_2words(u32 a, u32 b, u32 initval) +{ + return jhash3_3words(0, a, b, initval); +} + +static inline u32 jhash3_1word(u32 a, u32 initval) +{ + return jhash3_3words(0, 0, a, initval); +} + +#endif /* _LINUX_JHASH3_H */ -- 1.5.4.3 Best regards, Jozsef - E-mail : kadlec@xxxxxxxxxxxxxxxxx, kadlec@xxxxxxxxxxxx PGP key : http://www.kfki.hu/~kadlec/pgp_public_key.txt Address : KFKI Research Institute for Particle and Nuclear Physics H-1525 Budapest 114, POB. 49, Hungary -- 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
