1/*
2 * Copyright 2012-present 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#pragma once
18
19#include <folly/Fingerprint.h>
20#include <folly/Range.h>
21#include <folly/detail/FingerprintPolynomial.h>
22
23namespace folly {
24namespace detail {
25
26/**
27 * Slow, one-bit-at-a-time implementation of the Rabin fingerprint.
28 *
29 * This is useful as a reference implementation to test the Broder optimization
30 * for correctness in the unittest; it's probably too slow for any real use.
31 */
32template <int BITS>
33class SlowFingerprint {
34 public:
35 SlowFingerprint() : poly_(FingerprintTable<BITS>::poly) {
36 // Use the same starting value as Fingerprint, (1 << (BITS-1))
37 fp_.addXk(BITS - 1);
38 }
39
40 SlowFingerprint& update8(uint8_t v) {
41 updateLSB(v, 8);
42 return *this;
43 }
44
45 SlowFingerprint& update32(uint32_t v) {
46 updateLSB(v, 32);
47 return *this;
48 }
49
50 SlowFingerprint& update64(uint64_t v) {
51 updateLSB(v, 64);
52 return *this;
53 }
54
55 SlowFingerprint& update(const folly::StringPiece str) {
56 const char* p = str.start();
57 for (int i = str.size(); i != 0; p++, i--) {
58 update8(static_cast<uint8_t>(*p));
59 }
60 return *this;
61 }
62
63 void write(uint64_t* out) const {
64 for (int i = 0; i < fp_.size(); ++i) {
65 out[i] = fp_.get(i);
66 }
67 }
68
69 private:
70 void updateBit(bool bit) {
71 fp_.mulXmod(poly_);
72 if (bit) {
73 fp_.addXk(0);
74 }
75 }
76
77 void updateLSB(uint64_t val, int bits) {
78 val <<= (64 - bits);
79 for (; bits != 0; --bits) {
80 updateBit(val & (1ULL << 63));
81 val <<= 1;
82 }
83 }
84
85 const FingerprintPolynomial<BITS - 1> poly_;
86 FingerprintPolynomial<BITS - 1> fp_;
87};
88
89} // namespace detail
90} // namespace folly
91