зеркало из https://github.com/github/ruby.git
* string.c (hash): replaced by MurmurHash described in
<http://murmurhash.googlepages.com/>. git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@15743 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
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matz
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Коммит
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@ -1,3 +1,8 @@
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Tue Mar 11 10:19:10 2008 Yukihiro Matsumoto <matz@ruby-lang.org>
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* string.c (hash): replaced by MurmurHash described in
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<http://murmurhash.googlepages.com/>.
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Tue Mar 11 09:52:49 2008 Yukihiro Matsumoto <matz@ruby-lang.org>
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* string.c (rb_str_comparable): empty strings in any encoding are
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141
string.c
141
string.c
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@ -1685,122 +1685,41 @@ 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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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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--------------------------------------------------------------------
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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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--------------------------------------------------------------------
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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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/* MurmurHash described in http://murmurhash.googlepages.com/ */
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unsigned int
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hash(const unsigned char * data, int len, unsigned int h)
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{
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register ub4 a,b,c,len;
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const unsigned int m = 0x7fd652ad;
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const int r = 16;
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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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h += 0xdeadbeef;
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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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while(len >= 4) {
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h += *(unsigned int *)data;
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h *= m;
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h ^= h >> r;
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data += 4;
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len -= 4;
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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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switch(len) {
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case 3:
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h += data[2] << 16;
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case 2:
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h += data[1] << 8;
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case 1:
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h += data[0];
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h *= m;
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h ^= h >> r;
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};
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h *= m;
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h ^= h >> 10;
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h *= m;
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h ^= h >> 17;
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return h;
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}
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int
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