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* 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
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2 changed files with 118 additions and 88 deletions
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Wed Nov 1 23:01:55 2006 Yukihiro Matsumoto <matz@ruby-lang.org>
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* string.c (hash): use Bob Jenkins' hash algorithm.
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Wed Nov 1 02:22:31 2006 Akinori MUSHA <knu@iDaemons.org>
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* ext/digest/lib/digest/hmac.rb (Digest::HMAC::update): Minor
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202
string.c
202
string.c
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@ -879,102 +879,128 @@ rb_str_concat(VALUE str1, VALUE str2)
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return rb_str_append(str1, str2);
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}
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/*
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* hash_32 - 32 bit Fowler/Noll/Vo FNV-1a hash code
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*
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* @(#) $hash_32.Revision: 1.1 $
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* @(#) $hash_32.Id: hash_32a.c,v 1.1 2003/10/03 20:38:53 chongo Exp $
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* @(#) $hash_32.Source: /usr/local/src/cmd/fnv/RCS/hash_32a.c,v $
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*
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***
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*
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* Fowler/Noll/Vo hash
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*
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* The basis of this hash algorithm was taken from an idea sent
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* as reviewer comments to the IEEE POSIX P1003.2 committee by:
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*
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* Phong Vo (http://www.research.att.com/info/kpv/)
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* Glenn Fowler (http://www.research.att.com/~gsf/)
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*
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* In a subsequent ballot round:
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*
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* Landon Curt Noll (http://www.isthe.com/chongo/)
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*
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* improved on their algorithm. Some people tried this hash
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* and found that it worked rather well. In an EMail message
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* to Landon, they named it the ``Fowler/Noll/Vo'' or FNV hash.
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*
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* FNV hashes are designed to be fast while maintaining a low
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* collision rate. The FNV speed allows one to quickly hash lots
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* of data while maintaining a reasonable collision rate. See:
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*
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* http://www.isthe.com/chongo/tech/comp/fnv/index.html
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*
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* for more details as well as other forms of the FNV hash.
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***
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*
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* To use the recommended 32 bit FNV-1a hash, pass FNV1_32A_INIT as the
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* Fnv32_t hashval argument to fnv_32a_buf() or fnv_32a_str().
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*
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***
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*
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* Please do not copyright this code. This code is in the public domain.
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*
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* LANDON CURT NOLL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
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* INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO
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* EVENT SHALL LANDON CURT NOLL BE LIABLE FOR ANY SPECIAL, INDIRECT OR
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* CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
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* USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
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* OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
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* PERFORMANCE OF THIS SOFTWARE.
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*
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* By:
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* chongo <Landon Curt Noll> /\oo/\
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* http://www.isthe.com/chongo/
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*
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* Share and Enjoy! :-)
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*/
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typedef unsigned int ub4; /* unsigned 4-byte quantities */
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typedef unsigned char ub1; /* unsigned 1-byte quantities */
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#define hashsize(n) ((ub4)1<<(n))
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#define hashmask(n) (hashsize(n)-1)
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/*
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* 32 bit FNV-1 and FNV-1a non-zero initial basis
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*
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* The FNV-1 initial basis is the FNV-0 hash of the following 32 octets:
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*
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* chongo <Landon Curt Noll> /\../\
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*
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* NOTE: The \'s above are not back-slashing escape characters.
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* They are literal ASCII backslash 0x5c characters.
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*
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* NOTE: The FNV-1a initial basis is the same value as FNV-1 by definition.
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*/
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#define FNV1_32A_INIT 0x811c9dc5
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--------------------------------------------------------------------
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mix -- mix 3 32-bit values reversibly.
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For every delta with one or two bits set, and the deltas of all three
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high bits or all three low bits, whether the original value of a,b,c
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is almost all zero or is uniformly distributed,
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* If mix() is run forward or backward, at least 32 bits in a,b,c
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have at least 1/4 probability of changing.
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* If mix() is run forward, every bit of c will change between 1/3 and
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2/3 of the time. (Well, 22/100 and 78/100 for some 2-bit deltas.)
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mix() was built out of 36 single-cycle latency instructions in a
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structure that could supported 2x parallelism, like so:
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a -= b;
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a -= c; x = (c>>13);
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b -= c; a ^= x;
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b -= a; x = (a<<8);
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c -= a; b ^= x;
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c -= b; x = (b>>13);
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...
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Unfortunately, superscalar Pentiums and Sparcs can't take advantage
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of that parallelism. They've also turned some of those single-cycle
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latency instructions into multi-cycle latency instructions. Still,
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this is the fastest good hash I could find. There were about 2^^68
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to choose from. I only looked at a billion or so.
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--------------------------------------------------------------------
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*/
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#define mix(a,b,c) \
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{ \
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a -= b; a -= c; a ^= (c>>13); \
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b -= c; b -= a; b ^= (a<<8); \
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c -= a; c -= b; c ^= (b>>13); \
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a -= b; a -= c; a ^= (c>>12); \
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b -= c; b -= a; b ^= (a<<16); \
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c -= a; c -= b; c ^= (b>>5); \
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a -= b; a -= c; a ^= (c>>3); \
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b -= c; b -= a; b ^= (a<<10); \
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c -= a; c -= b; c ^= (b>>15); \
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}
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/*
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* 32 bit magic FNV-1a prime
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*/
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#define FNV_32_PRIME 0x01000193
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--------------------------------------------------------------------
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hash() -- hash a variable-length key into a 32-bit value
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k : the key (the unaligned variable-length array of bytes)
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len : the length of the key, counting by bytes
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initval : can be any 4-byte value
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Returns a 32-bit value. Every bit of the key affects every bit of
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the return value. Every 1-bit and 2-bit delta achieves avalanche.
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About 6*len+35 instructions.
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The best hash table sizes are powers of 2. There is no need to do
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mod a prime (mod is sooo slow!). If you need less than 32 bits,
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use a bitmask. For example, if you need only 10 bits, do
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h = (h & hashmask(10));
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In which case, the hash table should have hashsize(10) elements.
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If you are hashing n strings (ub1 **)k, do it like this:
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for (i=0, h=0; i<n; ++i) h = hash( k[i], len[i], h);
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By Bob Jenkins, 1996. bob_jenkins@burtleburtle.net. You may use this
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code any way you wish, private, educational, or commercial. It's free.
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See http://burtleburtle.net/bob/hash/evahash.html
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Use for hash table lookup, or anything where one collision in 2^^32 is
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acceptable. Do NOT use for cryptographic purposes.
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--------------------------------------------------------------------
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*/
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static ub4
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hash(const ub1 *k, ub4 length, ub4 initval)
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/* k: the key */
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/* length: the length of the key */
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/* initval: the previous hash, or an arbitrary value */
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{
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register ub4 a,b,c,len;
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/* Set up the internal state */
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len = length;
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a = b = 0x9e3779b9; /* the golden ratio; an arbitrary value */
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c = initval; /* the previous hash value */
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/*---------------------------------------- handle most of the key */
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while (len >= 12) {
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a += (k[0] +((ub4)k[1]<<8) +((ub4)k[2]<<16) +((ub4)k[3]<<24));
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b += (k[4] +((ub4)k[5]<<8) +((ub4)k[6]<<16) +((ub4)k[7]<<24));
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c += (k[8] +((ub4)k[9]<<8) +((ub4)k[10]<<16)+((ub4)k[11]<<24));
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mix(a,b,c);
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k += 12; len -= 12;
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}
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/*------------------------------------- handle the last 11 bytes */
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c += length;
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switch(len) /* all the case statements fall through */
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{
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case 11: c+=((ub4)k[10]<<24);
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case 10: c+=((ub4)k[9]<<16);
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case 9 : c+=((ub4)k[8]<<8);
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/* the first byte of c is reserved for the length */
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case 8 : b+=((ub4)k[7]<<24);
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case 7 : b+=((ub4)k[6]<<16);
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case 6 : b+=((ub4)k[5]<<8);
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case 5 : b+=k[4];
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case 4 : a+=((ub4)k[3]<<24);
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case 3 : a+=((ub4)k[2]<<16);
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case 2 : a+=((ub4)k[1]<<8);
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case 1 : a+=k[0];
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/* case 0: nothing left to add */
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}
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mix(a,b,c);
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/*-------------------------------------------- report the result */
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return c;
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}
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int
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rb_memhash(const void *ptr, long len)
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{
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register const unsigned char *p = ptr;
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register unsigned int hval = FNV1_32A_INIT;
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/*
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* FNV-1a hash each octet in the buffer
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*/
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while (len--) {
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/* xor the bottom with the current octet */
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hval ^= (unsigned int)*p++;
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/* multiply by the 32 bit FNV magic prime mod 2^32 */
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#if defined(FNV_GCC_OPTIMIZATION)
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hval += (hval<<1) + (hval<<4) + (hval<<7) + (hval<<8) + (hval<<24);
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#else
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hval *= FNV_32_PRIME;
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#endif
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}
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return hval;
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return hash(ptr, len, 0);
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}
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int
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