ceph/src/googletest/googletest/samples/prime_tables.h

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  29
  30
  31
  32 // This provides interface PrimeTable that determines whether a number is a
  33 // prime and determines a next prime number. This interface is used
  34 // in Google Test samples demonstrating use of parameterized tests.
  35
  36 #ifndef GTEST_SAMPLES_PRIME_TABLES_H_
  37 #define GTEST_SAMPLES_PRIME_TABLES_H_
  38
  39 #include <algorithm>
  40
  41 // The prime table interface.
  42 class PrimeTable {
  43  public:
  44   virtual ~PrimeTable() {}
  45
  46   // Returns true if and only if n is a prime number.
  47   virtual bool IsPrime(int n) const = 0;
  48
  49   // Returns the smallest prime number greater than p; or returns -1
  50   // if the next prime is beyond the capacity of the table.
  51   virtual int GetNextPrime(int p) const = 0;
  52 };
  53
  54 // Implementation #1 calculates the primes on-the-fly.
  55 class OnTheFlyPrimeTable : public PrimeTable {
  56  public:
  57   bool IsPrime(int n) const override {
  58     if (n <= 1) return false;
  59
  60     for (int i = 2; i*i <= n; i++) {
  61       // n is divisible by an integer other than 1 and itself.
  62       if ((n % i) == 0) return false;
  63     }
  64
  65     return true;
  66   }
  67
  68   int GetNextPrime(int p) const override {
  69     for (int n = p + 1; n > 0; n++) {
  70       if (IsPrime(n)) return n;
  71     }
  72
  73     return -1;
  74   }
  75 };
  76
  77 // Implementation #2 pre-calculates the primes and stores the result
  78 // in an array.
  79 class PreCalculatedPrimeTable : public PrimeTable {
  80  public:
  81   // 'max' specifies the maximum number the prime table holds.
  82   explicit PreCalculatedPrimeTable(int max)
  83       : is_prime_size_(max + 1), is_prime_(new bool[max + 1]) {
  84     CalculatePrimesUpTo(max);
  85   }
  86   ~PreCalculatedPrimeTable() override { delete[] is_prime_; }
  87
  88   bool IsPrime(int n) const override {
  89     return 0 <= n && n < is_prime_size_ && is_prime_[n];
  90   }
  91
  92   int GetNextPrime(int p) const override {
  93     for (int n = p + 1; n < is_prime_size_; n++) {
  94       if (is_prime_[n]) return n;
  95     }
  96
  97     return -1;
  98   }
  99
 100  private:
 101   void CalculatePrimesUpTo(int max) {
 102     ::std::fill(is_prime_, is_prime_ + is_prime_size_, true);
 103     is_prime_[0] = is_prime_[1] = false;
 104
 105     // Checks every candidate for prime number (we know that 2 is the only even
 106     // prime).
 107     for (int i = 2; i*i <= max; i += i%2+1) {
 108       if (!is_prime_[i]) continue;
 109
 110       // Marks all multiples of i (except i itself) as non-prime.
 111       // We are starting here from i-th multiplier, because all smaller
 112       // complex numbers were already marked.
 113       for (int j = i*i; j <= max; j += i) {
 114         is_prime_[j] = false;
 115       }
 116     }
 117   }
 118
 119   const int is_prime_size_;
 120   bool* const is_prime_;
 121
 122   // Disables compiler warning "assignment operator could not be generated."
 123   void operator=(const PreCalculatedPrimeTable& rhs);
 124 };
 125
 126 #endif  // GTEST_SAMPLES_PRIME_TABLES_H_