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30 // Author: wan@google.com (Zhanyong Wan)
31 // Author: vladl@google.com (Vlad Losev)
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.
37 #ifndef GTEST_SAMPLES_PRIME_TABLES_H_
38 #define GTEST_SAMPLES_PRIME_TABLES_H_
42 // The prime table interface.
45 virtual ~PrimeTable() {}
47 // Returns true iff n is a prime number.
48 virtual bool IsPrime(int n) const = 0;
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;
55 // Implementation #1 calculates the primes on-the-fly.
56 class OnTheFlyPrimeTable : public PrimeTable {
58 virtual bool IsPrime(int n) const {
59 if (n <= 1) return false;
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;
69 virtual int GetNextPrime(int p) const {
70 for (int n = p + 1; n > 0; n++) {
71 if (IsPrime(n)) return n;
78 // Implementation #2 pre-calculates the primes and stores the result
80 class PreCalculatedPrimeTable : public PrimeTable {
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);
87 virtual ~PreCalculatedPrimeTable() { delete[] is_prime_; }
89 virtual bool IsPrime(int n) const {
90 return 0 <= n && n < is_prime_size_ && is_prime_[n];
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;
102 void CalculatePrimesUpTo(int max) {
103 ::std::fill(is_prime_, is_prime_ + is_prime_size_, true);
104 is_prime_[0] = is_prime_[1] = false;
106 for (int i = 2; i <= max; i++) {
107 if (!is_prime_[i]) continue;
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;
116 const int is_prime_size_;
117 bool* const is_prime_;
119 // Disables compiler warning "assignment operator could not be generated."
120 void operator=(const PreCalculatedPrimeTable& rhs);
123 #endif // GTEST_SAMPLES_PRIME_TABLES_H_