Le jeudi 25 novembre 2010 Ã 14:15 +0100, Jozsef Kadlecsik a Ãcrit : > 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 However, lookup2() is outdated as Bob wrote a new hash function called 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 > ... 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 netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
