text: // Copyright 2008 Google Inc.
  // All Rights Reserved.
  //
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are
  // met:
  //
  //     * Redistributions of source code must retain the above copyright
  // notice, this list of conditions and the following disclaimer.
  //     * Redistributions in binary form must reproduce the above
  // copyright notice, this list of conditions and the following disclaimer
  // in the documentation and/or other materials provided with the
  // distribution.
  //     * Neither the name of Google Inc. nor the names of its
  // contributors may be used to endorse or promote products derived from
  // this software without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  //
  // Author: wan@google.com (Zhanyong Wan)
  // Author: vladl@google.com (Vlad Losev)
  
  // This provides interface PrimeTable that determines whether a number is a
  // prime and determines a next prime number. This interface is used
  // in Google Test samples demonstrating use of parameterized tests.
  
  #ifndef GTEST_SAMPLES_PRIME_TABLES_H_
  #define GTEST_SAMPLES_PRIME_TABLES_H_
  
  #include <algorithm>
  
  // The prime table interface.
  class PrimeTable {
   public:
    virtual ~PrimeTable() {}
  
    // Returns true iff n is a prime number.
    virtual bool IsPrime(int n) const = 0;
  
    // Returns the smallest prime number greater than p; or returns -1
    // if the next prime is beyond the capacity of the table.
    virtual int GetNextPrime(int p) const = 0;
  };
  
  // Implementation #1 calculates the primes on-the-fly.
  class OnTheFlyPrimeTable : public PrimeTable {
   public:
    virtual bool IsPrime(int n) const {
      if (n <= 1) return false;
  
      for (int i = 2; i*i <= n; i++) {
        // n is divisible by an integer other than 1 and itself.
        if ((n % i) == 0) return false;
      }
  
      return true;
    }
  
    virtual int GetNextPrime(int p) const {
      for (int n = p + 1; n > 0; n++) {
        if (IsPrime(n)) return n;
      }
  
      return -1;
    }
  };
  
  // Implementation #2 pre-calculates the primes and stores the result
  // in an array.
  class PreCalculatedPrimeTable : public PrimeTable {
   public:
    // 'max' specifies the maximum number the prime table holds.
    explicit PreCalculatedPrimeTable(int max)
        : is_prime_size_(max + 1), is_prime_(new bool[max + 1]) {
      CalculatePrimesUpTo(max);
    }
    virtual ~PreCalculatedPrimeTable() { delete[] is_prime_; }
  
    virtual bool IsPrime(int n) const {
      return 0 <= n && n < is_prime_size_ && is_prime_[n];
    }
  
    virtual int GetNextPrime(int p) const {
      for (int n = p + 1; n < is_prime_size_; n++) {
        if (is_prime_[n]) return n;
      }
  
      return -1;
    }
  
   private:
    void CalculatePrimesUpTo(int max) {
      ::std::fill(is_prime_, is_prime_ + is_prime_size_, true);
      is_prime_[0] = is_prime_[1] = false;
  
      for (int i = 2; i <= max; i++) {
        if (!is_prime_[i]) continue;
  
        // Marks all multiples of i (except i itself) as non-prime.
        for (int j = 2*i; j <= max; j += i) {
          is_prime_[j] = false;
        }
      }
    }
  
    const int is_prime_size_;
    bool* const is_prime_;
  };
  
  #endif  // GTEST_SAMPLES_PRIME_TABLES_H_
  