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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.
42class PrimeTable {
43 public:
44  virtual ~PrimeTable() {}
45
46  // Returns true iff 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.
55class OnTheFlyPrimeTable : public PrimeTable {
56 public:
57  virtual bool IsPrime(int n) const {
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  virtual int GetNextPrime(int p) const {
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.
79class 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  virtual ~PreCalculatedPrimeTable() { delete[] is_prime_; }
87
88  virtual bool IsPrime(int n) const {
89    return 0 <= n && n < is_prime_size_ && is_prime_[n];
90  }
91
92  virtual int GetNextPrime(int p) const {
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_
127