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ff25e3b @tudor Add Bob Jenkins's SpookyHash to folly.
tudor authored
1 /*
2 * Copyright 2012 Facebook, Inc.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 //
18 // SpookyHash: a 128-bit noncryptographic hash function
19 // By Bob Jenkins, public domain
20 // Oct 31 2010: alpha, framework + SpookyHash::Mix appears right
21 // Oct 31 2011: alpha again, Mix only good to 2^^69 but rest appears right
22 // Dec 31 2011: beta, improved Mix, tested it for 2-bit deltas
23 // Feb 2 2012: production, same bits as beta
24 // Feb 5 2012: adjusted definitions of uint* to be more portable
25 // Mar 30 2012: 3 bytes/cycle, not 4. Alpha was 4 but wasn't thorough enough.
26 //
27 // Up to 3 bytes/cycle for long messages. Reasonably fast for short messages.
28 // All 1 or 2 bit deltas achieve avalanche within 1% bias per output bit.
29 //
30 // This was developed for and tested on 64-bit x86-compatible processors.
31 // It assumes the processor is little-endian. There is a macro
32 // controlling whether unaligned reads are allowed (by default they are).
33 // This should be an equally good hash on big-endian machines, but it will
34 // compute different results on them than on little-endian machines.
35 //
36 // Google's CityHash has similar specs to SpookyHash, and CityHash is faster
37 // on some platforms. MD4 and MD5 also have similar specs, but they are orders
38 // of magnitude slower. CRCs are two or more times slower, but unlike
39 // SpookyHash, they have nice math for combining the CRCs of pieces to form
40 // the CRCs of wholes. There are also cryptographic hashes, but those are even
41 // slower than MD5.
42 //
43
44 #ifndef FOLLY_SPOOKYHASH_H_
45 #define FOLLY_SPOOKYHASH_H_
46
47 #include <cstddef>
48 #include <cstdint>
49
50 namespace folly {
51 namespace hash {
52
53 class SpookyHash
54 {
55 public:
56 //
57 // SpookyHash: hash a single message in one call, produce 128-bit output
58 //
59 static void Hash128(
60 const void *message, // message to hash
61 size_t length, // length of message in bytes
62 uint64_t *hash1, // in/out: in seed 1, out hash value 1
63 uint64_t *hash2); // in/out: in seed 2, out hash value 2
64
65 //
66 // Hash64: hash a single message in one call, return 64-bit output
67 //
68 static uint64_t Hash64(
69 const void *message, // message to hash
70 size_t length, // length of message in bytes
71 uint64_t seed) // seed
72 {
73 uint64_t hash1 = seed;
74 Hash128(message, length, &hash1, &seed);
75 return hash1;
76 }
77
78 //
79 // Hash32: hash a single message in one call, produce 32-bit output
80 //
81 static uint32_t Hash32(
82 const void *message, // message to hash
83 size_t length, // length of message in bytes
84 uint32_t seed) // seed
85 {
86 uint64_t hash1 = seed, hash2 = seed;
87 Hash128(message, length, &hash1, &hash2);
88 return (uint32_t)hash1;
89 }
90
91 //
92 // Init: initialize the context of a SpookyHash
93 //
94 void Init(
95 uint64_t seed1, // any 64-bit value will do, including 0
96 uint64_t seed2); // different seeds produce independent hashes
97
98 //
99 // Update: add a piece of a message to a SpookyHash state
100 //
101 void Update(
102 const void *message, // message fragment
103 size_t length); // length of message fragment in bytes
104
105
106 //
107 // Final: compute the hash for the current SpookyHash state
108 //
109 // This does not modify the state; you can keep updating it afterward
110 //
111 // The result is the same as if SpookyHash() had been called with
112 // all the pieces concatenated into one message.
113 //
114 void Final(
115 uint64_t *hash1, // out only: first 64 bits of hash value.
116 uint64_t *hash2); // out only: second 64 bits of hash value.
117
118 //
119 // left rotate a 64-bit value by k bytes
120 //
121 static inline uint64_t Rot64(uint64_t x, int k)
122 {
123 return (x << k) | (x >> (64 - k));
124 }
125
126 //
127 // This is used if the input is 96 bytes long or longer.
128 //
129 // The internal state is fully overwritten every 96 bytes.
130 // Every input bit appears to cause at least 128 bits of entropy
131 // before 96 other bytes are combined, when run forward or backward
132 // For every input bit,
133 // Two inputs differing in just that input bit
134 // Where "differ" means xor or subtraction
135 // And the base value is random
136 // When run forward or backwards one Mix
137 // I tried 3 pairs of each; they all differed by at least 212 bits.
138 //
139 static inline void Mix(
140 const uint64_t *data,
141 uint64_t &s0, uint64_t &s1, uint64_t &s2, uint64_t &s3,
142 uint64_t &s4, uint64_t &s5, uint64_t &s6, uint64_t &s7,
143 uint64_t &s8, uint64_t &s9, uint64_t &s10,uint64_t &s11)
144 {
145 s0 += data[0]; s2 ^= s10; s11 ^= s0; s0 = Rot64(s0,11); s11 += s1;
146 s1 += data[1]; s3 ^= s11; s0 ^= s1; s1 = Rot64(s1,32); s0 += s2;
147 s2 += data[2]; s4 ^= s0; s1 ^= s2; s2 = Rot64(s2,43); s1 += s3;
148 s3 += data[3]; s5 ^= s1; s2 ^= s3; s3 = Rot64(s3,31); s2 += s4;
149 s4 += data[4]; s6 ^= s2; s3 ^= s4; s4 = Rot64(s4,17); s3 += s5;
150 s5 += data[5]; s7 ^= s3; s4 ^= s5; s5 = Rot64(s5,28); s4 += s6;
151 s6 += data[6]; s8 ^= s4; s5 ^= s6; s6 = Rot64(s6,39); s5 += s7;
152 s7 += data[7]; s9 ^= s5; s6 ^= s7; s7 = Rot64(s7,57); s6 += s8;
153 s8 += data[8]; s10 ^= s6; s7 ^= s8; s8 = Rot64(s8,55); s7 += s9;
154 s9 += data[9]; s11 ^= s7; s8 ^= s9; s9 = Rot64(s9,54); s8 += s10;
155 s10 += data[10]; s0 ^= s8; s9 ^= s10; s10 = Rot64(s10,22); s9 += s11;
156 s11 += data[11]; s1 ^= s9; s10 ^= s11; s11 = Rot64(s11,46); s10 += s0;
157 }
158
159 //
160 // Mix all 12 inputs together so that h0, h1 are a hash of them all.
161 //
162 // For two inputs differing in just the input bits
163 // Where "differ" means xor or subtraction
164 // And the base value is random, or a counting value starting at that bit
165 // The final result will have each bit of h0, h1 flip
166 // For every input bit,
167 // with probability 50 +- .3%
168 // For every pair of input bits,
169 // with probability 50 +- 3%
170 //
171 // This does not rely on the last Mix() call having already mixed some.
172 // Two iterations was almost good enough for a 64-bit result, but a
173 // 128-bit result is reported, so End() does three iterations.
174 //
175 static inline void EndPartial(
176 uint64_t &h0, uint64_t &h1, uint64_t &h2, uint64_t &h3,
177 uint64_t &h4, uint64_t &h5, uint64_t &h6, uint64_t &h7,
178 uint64_t &h8, uint64_t &h9, uint64_t &h10,uint64_t &h11)
179 {
180 h11+= h1; h2 ^= h11; h1 = Rot64(h1,44);
181 h0 += h2; h3 ^= h0; h2 = Rot64(h2,15);
182 h1 += h3; h4 ^= h1; h3 = Rot64(h3,34);
183 h2 += h4; h5 ^= h2; h4 = Rot64(h4,21);
184 h3 += h5; h6 ^= h3; h5 = Rot64(h5,38);
185 h4 += h6; h7 ^= h4; h6 = Rot64(h6,33);
186 h5 += h7; h8 ^= h5; h7 = Rot64(h7,10);
187 h6 += h8; h9 ^= h6; h8 = Rot64(h8,13);
188 h7 += h9; h10^= h7; h9 = Rot64(h9,38);
189 h8 += h10; h11^= h8; h10= Rot64(h10,53);
190 h9 += h11; h0 ^= h9; h11= Rot64(h11,42);
191 h10+= h0; h1 ^= h10; h0 = Rot64(h0,54);
192 }
193
194 static inline void End(
195 uint64_t &h0, uint64_t &h1, uint64_t &h2, uint64_t &h3,
196 uint64_t &h4, uint64_t &h5, uint64_t &h6, uint64_t &h7,
197 uint64_t &h8, uint64_t &h9, uint64_t &h10,uint64_t &h11)
198 {
199 EndPartial(h0,h1,h2,h3,h4,h5,h6,h7,h8,h9,h10,h11);
200 EndPartial(h0,h1,h2,h3,h4,h5,h6,h7,h8,h9,h10,h11);
201 EndPartial(h0,h1,h2,h3,h4,h5,h6,h7,h8,h9,h10,h11);
202 }
203
204 //
205 // The goal is for each bit of the input to expand into 128 bits of
206 // apparent entropy before it is fully overwritten.
207 // n trials both set and cleared at least m bits of h0 h1 h2 h3
208 // n: 2 m: 29
209 // n: 3 m: 46
210 // n: 4 m: 57
211 // n: 5 m: 107
212 // n: 6 m: 146
213 // n: 7 m: 152
214 // when run forwards or backwards
215 // for all 1-bit and 2-bit diffs
216 // with diffs defined by either xor or subtraction
217 // with a base of all zeros plus a counter, or plus another bit, or random
218 //
219 static inline void ShortMix(uint64_t &h0, uint64_t &h1, uint64_t &h2, uint64_t &h3)
220 {
221 h2 = Rot64(h2,50); h2 += h3; h0 ^= h2;
222 h3 = Rot64(h3,52); h3 += h0; h1 ^= h3;
223 h0 = Rot64(h0,30); h0 += h1; h2 ^= h0;
224 h1 = Rot64(h1,41); h1 += h2; h3 ^= h1;
225 h2 = Rot64(h2,54); h2 += h3; h0 ^= h2;
226 h3 = Rot64(h3,48); h3 += h0; h1 ^= h3;
227 h0 = Rot64(h0,38); h0 += h1; h2 ^= h0;
228 h1 = Rot64(h1,37); h1 += h2; h3 ^= h1;
229 h2 = Rot64(h2,62); h2 += h3; h0 ^= h2;
230 h3 = Rot64(h3,34); h3 += h0; h1 ^= h3;
231 h0 = Rot64(h0,5); h0 += h1; h2 ^= h0;
232 h1 = Rot64(h1,36); h1 += h2; h3 ^= h1;
233 }
234
235 //
236 // Mix all 4 inputs together so that h0, h1 are a hash of them all.
237 //
238 // For two inputs differing in just the input bits
239 // Where "differ" means xor or subtraction
240 // And the base value is random, or a counting value starting at that bit
241 // The final result will have each bit of h0, h1 flip
242 // For every input bit,
243 // with probability 50 +- .3% (it is probably better than that)
244 // For every pair of input bits,
245 // with probability 50 +- .75% (the worst case is approximately that)
246 //
247 static inline void ShortEnd(uint64_t &h0, uint64_t &h1, uint64_t &h2, uint64_t &h3)
248 {
249 h3 ^= h2; h2 = Rot64(h2,15); h3 += h2;
250 h0 ^= h3; h3 = Rot64(h3,52); h0 += h3;
251 h1 ^= h0; h0 = Rot64(h0,26); h1 += h0;
252 h2 ^= h1; h1 = Rot64(h1,51); h2 += h1;
253 h3 ^= h2; h2 = Rot64(h2,28); h3 += h2;
254 h0 ^= h3; h3 = Rot64(h3,9); h0 += h3;
255 h1 ^= h0; h0 = Rot64(h0,47); h1 += h0;
256 h2 ^= h1; h1 = Rot64(h1,54); h2 += h1;
257 h3 ^= h2; h2 = Rot64(h2,32); h3 += h2;
258 h0 ^= h3; h3 = Rot64(h3,25); h0 += h3;
259 h1 ^= h0; h0 = Rot64(h0,63); h1 += h0;
260 }
261
262 private:
263
264 //
265 // Short is used for messages under 192 bytes in length
266 // Short has a low startup cost, the normal mode is good for long
267 // keys, the cost crossover is at about 192 bytes. The two modes were
268 // held to the same quality bar.
269 //
270 static void Short(
271 const void *message, // message (array of bytes, not necessarily aligned)
272 size_t length, // length of message (in bytes)
273 uint64_t *hash1, // in/out: in the seed, out the hash value
274 uint64_t *hash2); // in/out: in the seed, out the hash value
275
276 // number of uint64_t's in internal state
277 static const size_t sc_numVars = 12;
278
279 // size of the internal state
280 static const size_t sc_blockSize = sc_numVars*8;
281
282 // size of buffer of unhashed data, in bytes
283 static const size_t sc_bufSize = 2*sc_blockSize;
284
285 //
286 // sc_const: a constant which:
287 // * is not zero
288 // * is odd
289 // * is a not-very-regular mix of 1's and 0's
290 // * does not need any other special mathematical properties
291 //
292 static const uint64_t sc_const = 0xdeadbeefdeadbeefLL;
293
294 uint64_t m_data[2*sc_numVars]; // unhashed data, for partial messages
295 uint64_t m_state[sc_numVars]; // internal state of the hash
296 size_t m_length; // total length of the input so far
297 uint8_t m_remainder; // length of unhashed data stashed in m_data
298 };
299
300 } // namespace hash
301 } // namespace folly
302
303 #endif
304
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