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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.
36 #ifndef GTEST_SAMPLES_PRIME_TABLES_H_
37 #define GTEST_SAMPLES_PRIME_TABLES_H_
41 // The prime table interface.
44 virtual ~PrimeTable() {}
46 // Returns true iff n is a prime number.
47 virtual bool IsPrime(int n) const = 0;
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;
54 // Implementation #1 calculates the primes on-the-fly.
55 class OnTheFlyPrimeTable : public PrimeTable {
57 virtual bool IsPrime(int n) const {
58 if (n <= 1) return false;
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;
68 virtual int GetNextPrime(int p) const {
69 for (int n = p + 1; n > 0; n++) {
70 if (IsPrime(n)) return n;
77 // Implementation #2 pre-calculates the primes and stores the result
79 class PreCalculatedPrimeTable : public PrimeTable {
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);
86 virtual ~PreCalculatedPrimeTable() { delete[] is_prime_; }
88 virtual bool IsPrime(int n) const {
89 return 0 <= n && n < is_prime_size_ && is_prime_[n];
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;
101 void CalculatePrimesUpTo(int max) {
102 ::std::fill(is_prime_, is_prime_ + is_prime_size_, true);
103 is_prime_[0] = is_prime_[1] = false;
105 // Checks every candidate for prime number (we know that 2 is the only even
107 for (int i = 2; i*i <= max; i += i%2+1) {
108 if (!is_prime_[i]) continue;
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;
119 const int is_prime_size_;
120 bool* const is_prime_;
122 // Disables compiler warning "assignment operator could not be generated."
123 void operator=(const PreCalculatedPrimeTable& rhs);
126 #endif // GTEST_SAMPLES_PRIME_TABLES_H_