Message ID | 1290690908-794-3-git-send-email-kadlec@blackhole.kfki.hu |
---|---|
State | Changes Requested, archived |
Delegated to: | David Miller |
Headers | show |
Le jeudi 25 novembre 2010 à 14:15 +0100, Jozsef Kadlecsik a écrit : > 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 However, lookup2() is outdated as Bob wrote a new hash function called 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@blackhole.kfki.hu> > --- > 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 > ... I agree jhash() should be not be inlined. I am not sure for other variants. > +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); disassembly code on x86_32 for the previous line : 26: 66 90 xchg %ax,%ax 28: 0f b6 72 01 movzbl 0x1(%edx),%esi 2c: 0f b6 4a 02 movzbl 0x2(%edx),%ecx 30: c1 e6 08 shl $0x8,%esi 33: c1 e1 10 shl $0x10,%ecx 36: 8d 0c 0e lea (%esi,%ecx,1),%ecx 39: 0f b6 32 movzbl (%edx),%esi 3c: 8d 34 31 lea (%ecx,%esi,1),%esi 3f: 0f b6 4a 03 movzbl 0x3(%edx),%ecx 43: c1 e1 18 shl $0x18,%ecx 46: 8d 0c 0e lea (%esi,%ecx,1),%ecx or (CONFIG_CC_OPTIMIZE_FOR_SIZE=y) : 1b: 0f b6 7b 01 movzbl 0x1(%ebx),%edi 1f: c1 e7 08 shl $0x8,%edi 22: 89 7d f0 mov %edi,-0x10(%ebp) 25: 0f b6 7b 02 movzbl 0x2(%ebx),%edi 29: c1 e7 10 shl $0x10,%edi 2c: 03 7d f0 add -0x10(%ebp),%edi 2f: 89 7d f0 mov %edi,-0x10(%ebp) 32: 0f b6 3b movzbl (%ebx),%edi 35: 03 7d f0 add -0x10(%ebp),%edi 38: 89 7d f0 mov %edi,-0x10(%ebp) 3b: 0f b6 7b 03 movzbl 0x3(%ebx),%edi 3f: c1 e7 18 shl $0x18,%edi 42: 03 7d f0 add -0x10(%ebp),%edi I suggest : #include <linux/unaligned/packed_struct.h> ... a += __get_unaligned_cpu32(k); b += __get_unaligned_cpu32(k+4); c += __get_unaligned_cpu32(k+8); Fits nicely in registers. > + 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); -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, Nov 25, 2010 at 9:49 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote: > Le jeudi 25 novembre 2010 à 14:15 +0100, Jozsef Kadlecsik a écrit : >> 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@blackhole.kfki.hu> >> --- >> 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 >> > ... > > I agree jhash() should be not be inlined. > > I am not sure for other variants. > >> +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); > > disassembly code on x86_32 for the previous line : > > 26: 66 90 xchg %ax,%ax > 28: 0f b6 72 01 movzbl 0x1(%edx),%esi > 2c: 0f b6 4a 02 movzbl 0x2(%edx),%ecx > 30: c1 e6 08 shl $0x8,%esi > 33: c1 e1 10 shl $0x10,%ecx > 36: 8d 0c 0e lea (%esi,%ecx,1),%ecx > 39: 0f b6 32 movzbl (%edx),%esi > 3c: 8d 34 31 lea (%ecx,%esi,1),%esi > 3f: 0f b6 4a 03 movzbl 0x3(%edx),%ecx > 43: c1 e1 18 shl $0x18,%ecx > 46: 8d 0c 0e lea (%esi,%ecx,1),%ecx > > or (CONFIG_CC_OPTIMIZE_FOR_SIZE=y) : > > 1b: 0f b6 7b 01 movzbl 0x1(%ebx),%edi > 1f: c1 e7 08 shl $0x8,%edi > 22: 89 7d f0 mov %edi,-0x10(%ebp) > 25: 0f b6 7b 02 movzbl 0x2(%ebx),%edi > 29: c1 e7 10 shl $0x10,%edi > 2c: 03 7d f0 add -0x10(%ebp),%edi > 2f: 89 7d f0 mov %edi,-0x10(%ebp) > 32: 0f b6 3b movzbl (%ebx),%edi > 35: 03 7d f0 add -0x10(%ebp),%edi > 38: 89 7d f0 mov %edi,-0x10(%ebp) > 3b: 0f b6 7b 03 movzbl 0x3(%ebx),%edi > 3f: c1 e7 18 shl $0x18,%edi > 42: 03 7d f0 add -0x10(%ebp),%edi > > > I suggest : > > #include <linux/unaligned/packed_struct.h> > ... > a += __get_unaligned_cpu32(k); > b += __get_unaligned_cpu32(k+4); > c += __get_unaligned_cpu32(k+8); > > Fits nicely in registers. > I think you mean get_unaligned_le32().
Le jeudi 25 novembre 2010 à 21:55 +0800, Changli Gao a écrit : > > I suggest : > > > > #include <linux/unaligned/packed_struct.h> > > ... > > a += __get_unaligned_cpu32(k); > > b += __get_unaligned_cpu32(k+4); > > c += __get_unaligned_cpu32(k+8); > > > > Fits nicely in registers. > > > > I think you mean get_unaligned_le32(). > No, I meant __get_unaligned_cpu32() We do same thing in jhash2() : a += k[0]; b += k[1]; c += k[2]; We dont care of bit order of the 32bit quantity we are adding to a,b or c , as long its consistent for the current machine ;) get_unaligned_le32() would be slow on big endian arches. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, 25 Nov 2010 11:45:08 pm Jozsef Kadlecsik wrote: > 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 Oops, we discussed this ages ago, looks like it fell through the cracks. Thanks Jozsef! > +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); This last one can be marked __attribute__((const)) for a little extra compiler help, too. Cheers, Rusty. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Hi, 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(). There is a longer comparison of those two and other hash functions at http://burtleburtle.net/bob/hash/doobs.html. Please consider applying the following patches. Speed I wrote a small benchmark program to compare jhash2 and jhash3 (you can download it from http://www.kfki.hu/~kadlec/sw/netfilter/jhash23.tgz). On a machine with Core2 Duo and compiled with -O2, the ratio of the execution time for the byte variants of the hash functions were (in parens the different key sizes): jhash2/jhash3 (4 bytes): 1.587518 jhash2/jhash3 (8 bytes): 1.282824 jhash2/jhash3 (12 bytes): 2.349628 jhash2/jhash3 (16 bytes): 1.466988 jhash2/jhash3 (32 bytes): 1.501063 jhash2/jhash3 (64 bytes): 1.587527 jhash2/jhash3 (128 bytes): 1.628037 jhash2/jhash3 (256 bytes): 1.648318 Similarly, for the word variants jhash2/jhash3 (1 words): 1.300904 jhash2/jhash3 (2 words): 1.316108 jhash2/jhash3 (3 words): 2.249708 jhash2/jhash3 (4 words): 1.460192 jhash2/jhash3 (8 words): 1.501438 jhash2/jhash3 (16 words): 1.558039 jhash2/jhash3 (32 words): 1.520082 jhash2/jhash3 (64 words): 1.528347 Sizes When compiling just the byte variants the sizes are text data bss dec hex filename 661 0 0 661 295 jhashb2.o 441 0 0 441 1b9 jhashb3.o and for the word variants text data bss dec hex filename 354 0 0 354 162 jhashw2.o 248 0 0 248 f8 jhashw3.o I compiled the kernel with "allyesconfig", in three variants: jhash2, jhash3 and jhash3 un-inlined text data bss dec hex filename 69297477 11282083 35904032 116483592 6f16608 vmlinux.jhash2 69293829 11282083 35903728 116479640 6f15698 vmlinux.jhash3 69288578 11282083 35902336 116472997 6f13ca5 vmlinux.jhash3-uninlined With jhash3 we can gain 3.6k and un-inlining shrinks the code with an additional 5.2k. In the patch I left jhash(3) inlined. Uniformity According to Bob Jenkins, lookup3() mixes better than lookup2(): it passes the check that every input bit changes every output bit 50% of the time, while lookup2() failed it. In order to verify it I added jhash3 to the cttest program, which tests hash functions with (artifical, worst case) netfilter conntrack data and calculates the statistics (chi-square, probability of longest bucket, etc). You can find the program and the results here: http://www.kfki.hu/~kadlec/sw/netfilter/ct3/ - to sum up, lookup3() produces uniform key values and no weakness could be spotted. Many thanks to Eric Dumazet for his thorough reviewing. Dave applied the first patch to net-next-2.6. Jozsef Kadlecsik (2): Remove calls to jhash internals The new jhash implementation include/linux/jhash.h | 183 ++++++++++++++++++++++---------------- net/ipv6/inet6_connection_sock.c | 18 ++-- net/ipv6/reassembly.c | 36 ++++---- 3 files changed, 129 insertions(+), 108 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu> Date: Fri, 3 Dec 2010 13:38:59 +0100 > 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(). There is a longer comparison of those two and other hash > functions at http://burtleburtle.net/bob/hash/doobs.html. > > Please consider applying the following patches. Patch #1 is already in the net-next-2.6 tree, and as long as there are no major objections to the general crowd (including Rusty et al.) I am happy to put patch #2 into my tree as well. Rusty, does the current version of patch #2 look good to you? Thanks! -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, 9 Dec 2010 03:39:54 am David Miller wrote: > From: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu> > Date: Fri, 3 Dec 2010 13:38:59 +0100 > > > 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(). There is a longer comparison of those two and other hash > > functions at http://burtleburtle.net/bob/hash/doobs.html. > > > > Please consider applying the following patches. > > Patch #1 is already in the net-next-2.6 tree, and as long as there are > no major objections to the general crowd (including Rusty et al.) I am > happy to put patch #2 into my tree as well. > > Rusty, does the current version of patch #2 look good to you? Yes, 2/2 good. Thanks Jozsef! Acked-by: Rusty Russell <rusty@rustcorp.com.au> -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Rusty Russell <rusty@rustcorp.com.au> Date: Thu, 9 Dec 2010 07:53:45 +1030 > On Thu, 9 Dec 2010 03:39:54 am David Miller wrote: >> From: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu> >> Date: Fri, 3 Dec 2010 13:38:59 +0100 >> >> > 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(). There is a longer comparison of those two and other hash >> > functions at http://burtleburtle.net/bob/hash/doobs.html. >> > >> > Please consider applying the following patches. >> >> Patch #1 is already in the net-next-2.6 tree, and as long as there are >> no major objections to the general crowd (including Rusty et al.) I am >> happy to put patch #2 into my tree as well. >> >> Rusty, does the current version of patch #2 look good to you? > > Yes, 2/2 good. Thanks Jozsef! > > Acked-by: Rusty Russell <rusty@rustcorp.com.au> Applied, thanks everyone. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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@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. - * - * Copyright (C) 2003 David S. Miller (davem@redhat.com) - * - * 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@burtleburtle.net) + * + * 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@blackhole.kfki.hu) + * + * 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);
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@blackhole.kfki.hu> --- 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