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