91 lines
2.1 KiB
C++
91 lines
2.1 KiB
C++
/*
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* Copyright 2012-present Facebook, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#pragma once
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#include <folly/Fingerprint.h>
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#include <folly/Range.h>
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#include <folly/detail/FingerprintPolynomial.h>
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namespace folly {
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namespace detail {
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/**
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* Slow, one-bit-at-a-time implementation of the Rabin fingerprint.
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*
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* This is useful as a reference implementation to test the Broder optimization
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* for correctness in the unittest; it's probably too slow for any real use.
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*/
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template <int BITS>
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class SlowFingerprint {
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public:
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SlowFingerprint() : poly_(FingerprintTable<BITS>::poly) {
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// Use the same starting value as Fingerprint, (1 << (BITS-1))
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fp_.addXk(BITS - 1);
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}
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SlowFingerprint& update8(uint8_t v) {
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updateLSB(v, 8);
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return *this;
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}
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SlowFingerprint& update32(uint32_t v) {
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updateLSB(v, 32);
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return *this;
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}
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SlowFingerprint& update64(uint64_t v) {
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updateLSB(v, 64);
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return *this;
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}
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SlowFingerprint& update(const folly::StringPiece str) {
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const char* p = str.start();
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for (int i = str.size(); i != 0; p++, i--) {
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update8(static_cast<uint8_t>(*p));
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}
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return *this;
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}
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void write(uint64_t* out) const {
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for (int i = 0; i < fp_.size(); ++i) {
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out[i] = fp_.get(i);
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}
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}
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private:
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void updateBit(bool bit) {
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fp_.mulXmod(poly_);
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if (bit) {
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fp_.addXk(0);
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}
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}
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void updateLSB(uint64_t val, int bits) {
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val <<= (64 - bits);
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for (; bits != 0; --bits) {
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updateBit(val & (1ULL << 63));
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val <<= 1;
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}
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}
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const FingerprintPolynomial<BITS - 1> poly_;
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FingerprintPolynomial<BITS - 1> fp_;
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};
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} // namespace detail
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} // namespace folly
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