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prime_tables.h
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1// Copyright 2008 Google Inc.
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29
30// This provides interface PrimeTable that determines whether a number is a
31// prime and determines a next prime number. This interface is used
32// in Google Test samples demonstrating use of parameterized tests.
33
34#ifndef GOOGLETEST_SAMPLES_PRIME_TABLES_H_
35#define GOOGLETEST_SAMPLES_PRIME_TABLES_H_
36
37#include <algorithm>
38
39// The prime table interface.
41 public:
42 virtual ~PrimeTable() {}
43
44 // Returns true if and only if n is a prime number.
45 virtual bool IsPrime(int n) const = 0;
46
47 // Returns the smallest prime number greater than p; or returns -1
48 // if the next prime is beyond the capacity of the table.
49 virtual int GetNextPrime(int p) const = 0;
50};
51
52// Implementation #1 calculates the primes on-the-fly.
54 public:
55 bool IsPrime(int n) const override {
56 if (n <= 1) return false;
57
58 for (int i = 2; i * i <= n; i++) {
59 // n is divisible by an integer other than 1 and itself.
60 if ((n % i) == 0) return false;
61 }
62
63 return true;
64 }
65
66 int GetNextPrime(int p) const override {
67 if (p < 0) return -1;
68
69 for (int n = p + 1;; n++) {
70 if (IsPrime(n)) return n;
71 }
72 }
73};
74
75// Implementation #2 pre-calculates the primes and stores the result
76// in an array.
78 public:
79 // 'max' specifies the maximum number the prime table holds.
80 explicit PreCalculatedPrimeTable(int max)
81 : is_prime_size_(max + 1), is_prime_(new bool[max + 1]) {
82 CalculatePrimesUpTo(max);
83 }
84 ~PreCalculatedPrimeTable() override { delete[] is_prime_; }
85
86 bool IsPrime(int n) const override {
87 return 0 <= n && n < is_prime_size_ && is_prime_[n];
88 }
89
90 int GetNextPrime(int p) const override {
91 for (int n = p + 1; n < is_prime_size_; n++) {
92 if (is_prime_[n]) return n;
93 }
94
95 return -1;
96 }
97
98 private:
99 void CalculatePrimesUpTo(int max) {
100 ::std::fill(is_prime_, is_prime_ + is_prime_size_, true);
101 is_prime_[0] = is_prime_[1] = false;
102
103 // Checks every candidate for prime number (we know that 2 is the only even
104 // prime).
105 for (int i = 2; i * i <= max; i += i % 2 + 1) {
106 if (!is_prime_[i]) continue;
107
108 // Marks all multiples of i (except i itself) as non-prime.
109 // We are starting here from i-th multiplier, because all smaller
110 // complex numbers were already marked.
111 for (int j = i * i; j <= max; j += i) {
112 is_prime_[j] = false;
113 }
114 }
115 }
116
117 const int is_prime_size_;
118 bool* const is_prime_;
119
120 // Disables compiler warning "assignment operator could not be generated."
121 void operator=(const PreCalculatedPrimeTable& rhs);
122};
123
124#endif // GOOGLETEST_SAMPLES_PRIME_TABLES_H_
int GetNextPrime(int p) const override
bool IsPrime(int n) const override
int GetNextPrime(int p) const override
bool IsPrime(int n) const override
~PreCalculatedPrimeTable() override
virtual bool IsPrime(int n) const =0
virtual int GetNextPrime(int p) const =0
virtual ~PrimeTable()