yaml-cpp

prime_tables.h (4227B)

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 // Copyright 2008 Google Inc.
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 // modification, are permitted provided that the following conditions are
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 //
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 // 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.
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 // 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
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 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 
 
 // 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 if and only if 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:
   bool IsPrime(int n) const override {
     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;
   }
 
   int GetNextPrime(int p) const override {
     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);
   }
   ~PreCalculatedPrimeTable() override { delete[] is_prime_; }
 
   bool IsPrime(int n) const override {
     return 0 <= n && n < is_prime_size_ && is_prime_[n];
   }
 
   int GetNextPrime(int p) const override {
     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;
 
     // Checks every candidate for prime number (we know that 2 is the only even
     // prime).
     for (int i = 2; i*i <= max; i += i%2+1) {
       if (!is_prime_[i]) continue;
 
       // Marks all multiples of i (except i itself) as non-prime.
       // We are starting here from i-th multiplier, because all smaller
       // complex numbers were already marked.
       for (int j = i*i; j <= max; j += i) {
         is_prime_[j] = false;
       }
     }
   }
 
   const int is_prime_size_;
   bool* const is_prime_;
 
   // Disables compiler warning "assignment operator could not be generated."
   void operator=(const PreCalculatedPrimeTable& rhs);
 };
 
 #endif  // GTEST_SAMPLES_PRIME_TABLES_H_