text: /*
   * Copyright 2012-present 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.
   */
  
  #pragma once
  
  #include <folly/Fingerprint.h>
  #include <folly/Range.h>
  #include <folly/detail/FingerprintPolynomial.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 & (1ULL << 63));
        val <<= 1;
      }
    }
  
    const FingerprintPolynomial<BITS-1> poly_;
    FingerprintPolynomial<BITS-1> fp_;
  };
  
  } // namespace detail
  } // namespace folly
  