2 * Copyright 2012 Facebook, Inc.
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
8 * http://www.apache.org/licenses/LICENSE-2.0
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.
18 * Compute 64-, 96-, and 128-bit Rabin fingerprints, as described in
19 * Michael O. Rabin (1981)
20 * Fingerprinting by Random Polynomials
21 * Center for Research in Computing Technology, Harvard University
22 * Tech Report TR-CSE-03-01
24 * The implementation follows the optimization described in
25 * Andrei Z. Broder (1993)
26 * Some applications of Rabin's fingerprinting method
28 * extended for fingerprints larger than 64 bits, and modified to use
29 * 64-bit instead of 32-bit integers for computation.
31 * The precomputed tables are in FingerprintTable.cpp, which is automatically
32 * generated by ComputeFingerprintTable.cpp.
34 * Benchmarked on 10/13/2009 on a 2.5GHz quad-core Xeon L5420,
35 * - Fingerprint<64>::update64() takes about 12ns
36 * - Fingerprint<96>::update64() takes about 30ns
37 * - Fingerprint<128>::update128() takes about 30ns
38 * (unsurprisingly, Fingerprint<96> and Fingerprint<128> take the
39 * same amount of time, as they both use 128-bit operations; the least
40 * significant 32 bits of Fingerprint<96> will always be 0)
42 * @author Tudor Bosman (tudorb@facebook.com)
45 #ifndef FOLLY_FINGERPRINT_H_
46 #define FOLLY_FINGERPRINT_H_
50 #include "folly/Range.h"
56 struct FingerprintTable {
57 static const uint64_t poly[1 + (BITS-1)/64];
58 static const uint64_t table[8][256][1 + (BITS-1)/64];
63 * Compute the Rabin fingerprint.
65 * TODO(tudorb): Extend this to allow removing values from the computed
66 * fingerprint (so we can fingerprint a sliding window, as in the Rabin-Karp
67 * string matching algorithm)
69 * update* methods return *this, so you can chain them together:
70 * Fingerprint<96>().update8(x).update(str).update64(val).write(output);
76 // Use a non-zero starting value. We'll use (1 << (BITS-1))
78 for (int i = 1; i < size(); i++)
82 Fingerprint& update8(uint8_t v) {
83 uint8_t out = shlor8(v);
84 xortab(detail::FingerprintTable<BITS>::table[0][out]);
88 // update32 and update64 are convenience functions to update the fingerprint
89 // with 4 and 8 bytes at a time. They are faster than calling update8
90 // in a loop. They process the bytes in big-endian order.
91 Fingerprint& update32(uint32_t v) {
92 uint32_t out = shlor32(v);
93 for (int i = 0; i < 4; i++) {
94 xortab(detail::FingerprintTable<BITS>::table[i][out&0xff]);
100 Fingerprint& update64(uint64_t v) {
101 uint64_t out = shlor64(v);
102 for (int i = 0; i < 8; i++) {
103 xortab(detail::FingerprintTable<BITS>::table[i][out&0xff]);
109 Fingerprint& update(StringPiece str) {
110 // TODO(tudorb): We could be smart and do update64 or update32 if aligned
118 * Return the number of uint64s needed to hold the fingerprint value.
121 return 1 + (BITS-1)/64;
125 * Write the computed fingeprint to an array of size() uint64_t's.
126 * For Fingerprint<64>, size()==1; we write 64 bits in out[0]
127 * For Fingerprint<96>, size()==2; we write 64 bits in out[0] and
128 * the most significant 32 bits of out[1]
129 * For Fingerprint<128>, size()==2; we write 64 bits in out[0] and
132 void write(uint64_t* out) const {
133 for (int i = 0; i < size(); i++) {
139 // XOR the fingerprint with a value from one of the tables.
140 void xortab(const uint64_t* tab) {
141 for (int i = 0; i < size(); i++) {
146 // Helper functions: shift the fingerprint value left by 8/32/64 bits,
147 // return the "out" value (the bits that were shifted out), and add "v"
148 // in the bits on the right.
149 uint8_t shlor8(uint8_t v);
150 uint32_t shlor32(uint32_t v);
151 uint64_t shlor64(uint64_t v);
153 uint64_t fp_[1 + (BITS-1)/64];
156 // Convenience functions
159 * Return the 64-bit Rabin fingerprint of a string.
161 inline uint64_t fingerprint64(StringPiece str) {
163 Fingerprint<64>().update(str).write(&fp);
168 * Compute the 96-bit Rabin fingerprint of a string.
169 * Return the 64 most significant bits in *msb, and the 32 least significant
172 inline void fingerprint96(StringPiece str,
173 uint64_t* msb, uint32_t* lsb) {
175 Fingerprint<96>().update(str).write(fp);
177 *lsb = (uint32_t)(fp[1] >> 32);
181 * Compute the 128-bit Rabin fingerprint of a string.
182 * Return the 64 most significant bits in *msb, and the 64 least significant
185 inline void fingerprint128(StringPiece str,
186 uint64_t* msb, uint64_t* lsb) {
188 Fingerprint<128>().update(str).write(fp);
195 inline uint8_t Fingerprint<64>::shlor8(uint8_t v) {
196 uint8_t out = (uint8_t)(fp_[0] >> 56);
197 fp_[0] = (fp_[0] << 8) | ((uint64_t)v);
202 inline uint32_t Fingerprint<64>::shlor32(uint32_t v) {
203 uint32_t out = (uint32_t)(fp_[0] >> 32);
204 fp_[0] = (fp_[0] << 32) | ((uint64_t)v);
209 inline uint64_t Fingerprint<64>::shlor64(uint64_t v) {
210 uint64_t out = fp_[0];
216 inline uint8_t Fingerprint<96>::shlor8(uint8_t v) {
217 uint8_t out = (uint8_t)(fp_[0] >> 56);
218 fp_[0] = (fp_[0] << 8) | (fp_[1] >> 56);
219 fp_[1] = (fp_[1] << 8) | ((uint64_t)v << 32);
224 inline uint32_t Fingerprint<96>::shlor32(uint32_t v) {
225 uint32_t out = (uint32_t)(fp_[0] >> 32);
226 fp_[0] = (fp_[0] << 32) | (fp_[1] >> 32);
227 fp_[1] = ((uint64_t)v << 32);
232 inline uint64_t Fingerprint<96>::shlor64(uint64_t v) {
233 uint64_t out = fp_[0];
234 fp_[0] = fp_[1] | (v >> 32);
240 inline uint8_t Fingerprint<128>::shlor8(uint8_t v) {
241 uint8_t out = (uint8_t)(fp_[0] >> 56);
242 fp_[0] = (fp_[0] << 8) | (fp_[1] >> 56);
243 fp_[1] = (fp_[1] << 8) | ((uint64_t)v);
248 inline uint32_t Fingerprint<128>::shlor32(uint32_t v) {
249 uint32_t out = (uint32_t)(fp_[0] >> 32);
250 fp_[0] = (fp_[0] << 32) | (fp_[1] >> 32);
251 fp_[1] = (fp_[1] << 32) | ((uint64_t)v);
256 inline uint64_t Fingerprint<128>::shlor64(uint64_t v) {
257 uint64_t out = fp_[0];
265 #endif /* FOLLY_FINGERPRINT_H_ */