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