From 11e562f34afff4d657da12e85f959200207d6bd5 Mon Sep 17 00:00:00 2001 From: matz Date: Wed, 1 Nov 2006 14:23:42 +0000 Subject: * string.c (hash): use Bob Jenkins' hash algorithm. git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@11255 b2dd03c8-39d4-4d8f-98ff-823fe69b080e --- ChangeLog | 4 ++ string.c | 202 +++++++++++++++++++++++++++++++++++--------------------------- 2 files changed, 118 insertions(+), 88 deletions(-) diff --git a/ChangeLog b/ChangeLog index d9fb6adad1..01f56f5a2a 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,7 @@ +Wed Nov 1 23:01:55 2006 Yukihiro Matsumoto + + * string.c (hash): use Bob Jenkins' hash algorithm. + Wed Nov 1 02:22:31 2006 Akinori MUSHA * ext/digest/lib/digest/hmac.rb (Digest::HMAC::update): Minor diff --git a/string.c b/string.c index 529c375b4f..79fa217871 100644 --- a/string.c +++ b/string.c @@ -879,102 +879,128 @@ rb_str_concat(VALUE str1, VALUE str2) return rb_str_append(str1, str2); } -/* - * hash_32 - 32 bit Fowler/Noll/Vo FNV-1a hash code - * - * @(#) $hash_32.Revision: 1.1 $ - * @(#) $hash_32.Id: hash_32a.c,v 1.1 2003/10/03 20:38:53 chongo Exp $ - * @(#) $hash_32.Source: /usr/local/src/cmd/fnv/RCS/hash_32a.c,v $ - * - *** - * - * Fowler/Noll/Vo hash - * - * The basis of this hash algorithm was taken from an idea sent - * as reviewer comments to the IEEE POSIX P1003.2 committee by: - * - * Phong Vo (http://www.research.att.com/info/kpv/) - * Glenn Fowler (http://www.research.att.com/~gsf/) - * - * In a subsequent ballot round: - * - * Landon Curt Noll (http://www.isthe.com/chongo/) - * - * improved on their algorithm. Some people tried this hash - * and found that it worked rather well. In an EMail message - * to Landon, they named it the ``Fowler/Noll/Vo'' or FNV hash. - * - * FNV hashes are designed to be fast while maintaining a low - * collision rate. The FNV speed allows one to quickly hash lots - * of data while maintaining a reasonable collision rate. See: - * - * http://www.isthe.com/chongo/tech/comp/fnv/index.html - * - * for more details as well as other forms of the FNV hash. - *** - * - * To use the recommended 32 bit FNV-1a hash, pass FNV1_32A_INIT as the - * Fnv32_t hashval argument to fnv_32a_buf() or fnv_32a_str(). - * - *** - * - * Please do not copyright this code. This code is in the public domain. - * - * LANDON CURT NOLL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, - * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO - * EVENT SHALL LANDON CURT NOLL BE LIABLE FOR ANY SPECIAL, INDIRECT OR - * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF - * USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR - * OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR - * PERFORMANCE OF THIS SOFTWARE. - * - * By: - * chongo /\oo/\ - * http://www.isthe.com/chongo/ - * - * Share and Enjoy! :-) - */ +typedef unsigned int ub4; /* unsigned 4-byte quantities */ +typedef unsigned char ub1; /* unsigned 1-byte quantities */ + +#define hashsize(n) ((ub4)1<<(n)) +#define hashmask(n) (hashsize(n)-1) /* - * 32 bit FNV-1 and FNV-1a non-zero initial basis - * - * The FNV-1 initial basis is the FNV-0 hash of the following 32 octets: - * - * chongo /\../\ - * - * NOTE: The \'s above are not back-slashing escape characters. - * They are literal ASCII backslash 0x5c characters. - * - * NOTE: The FNV-1a initial basis is the same value as FNV-1 by definition. - */ -#define FNV1_32A_INIT 0x811c9dc5 +-------------------------------------------------------------------- +mix -- mix 3 32-bit values reversibly. +For every delta with one or two bits set, and the deltas of all three + high bits or all three low bits, whether the original value of a,b,c + is almost all zero or is uniformly distributed, +* If mix() is run forward or backward, at least 32 bits in a,b,c + have at least 1/4 probability of changing. +* If mix() is run forward, every bit of c will change between 1/3 and + 2/3 of the time. (Well, 22/100 and 78/100 for some 2-bit deltas.) +mix() was built out of 36 single-cycle latency instructions in a + structure that could supported 2x parallelism, like so: + a -= b; + a -= c; x = (c>>13); + b -= c; a ^= x; + b -= a; x = (a<<8); + c -= a; b ^= x; + c -= b; x = (b>>13); + ... + Unfortunately, superscalar Pentiums and Sparcs can't take advantage + of that parallelism. They've also turned some of those single-cycle + latency instructions into multi-cycle latency instructions. Still, + this is the fastest good hash I could find. There were about 2^^68 + to choose from. I only looked at a billion or so. +-------------------------------------------------------------------- +*/ +#define 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); \ +} /* - * 32 bit magic FNV-1a prime - */ -#define FNV_32_PRIME 0x01000193 +-------------------------------------------------------------------- +hash() -- hash a variable-length key into a 32-bit value + k : the key (the unaligned variable-length array of bytes) + len : the length of the key, counting by bytes + initval : can be any 4-byte value +Returns a 32-bit value. Every bit of the key affects every bit of +the return value. Every 1-bit and 2-bit delta achieves avalanche. +About 6*len+35 instructions. + +The best hash table sizes are powers of 2. There is no need to do +mod a prime (mod is sooo slow!). If you need less than 32 bits, +use a bitmask. For example, if you need only 10 bits, do + h = (h & hashmask(10)); +In which case, the hash table should have hashsize(10) elements. + +If you are hashing n strings (ub1 **)k, do it like this: + for (i=0, h=0; i= 12) { + a += (k[0] +((ub4)k[1]<<8) +((ub4)k[2]<<16) +((ub4)k[3]<<24)); + b += (k[4] +((ub4)k[5]<<8) +((ub4)k[6]<<16) +((ub4)k[7]<<24)); + c += (k[8] +((ub4)k[9]<<8) +((ub4)k[10]<<16)+((ub4)k[11]<<24)); + mix(a,b,c); + k += 12; len -= 12; + } + + /*------------------------------------- handle the last 11 bytes */ + c += length; + switch(len) /* all the case statements fall through */ + { + case 11: c+=((ub4)k[10]<<24); + case 10: c+=((ub4)k[9]<<16); + case 9 : c+=((ub4)k[8]<<8); + /* the first byte of c is reserved for the length */ + case 8 : b+=((ub4)k[7]<<24); + case 7 : b+=((ub4)k[6]<<16); + case 6 : b+=((ub4)k[5]<<8); + case 5 : b+=k[4]; + case 4 : a+=((ub4)k[3]<<24); + case 3 : a+=((ub4)k[2]<<16); + case 2 : a+=((ub4)k[1]<<8); + case 1 : a+=k[0]; + /* case 0: nothing left to add */ + } + mix(a,b,c); + /*-------------------------------------------- report the result */ + return c; +} int rb_memhash(const void *ptr, long len) { - register const unsigned char *p = ptr; - register unsigned int hval = FNV1_32A_INIT; - - /* - * FNV-1a hash each octet in the buffer - */ - while (len--) { - /* xor the bottom with the current octet */ - hval ^= (unsigned int)*p++; - - /* multiply by the 32 bit FNV magic prime mod 2^32 */ -#if defined(FNV_GCC_OPTIMIZATION) - hval += (hval<<1) + (hval<<4) + (hval<<7) + (hval<<8) + (hval<<24); -#else - hval *= FNV_32_PRIME; -#endif - } - return hval; + return hash(ptr, len, 0); } int -- cgit v1.2.3