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prime_tables.h
1 // Copyright 2008 Google Inc.
2 // All Rights Reserved.
3 //
4 // Redistribution and use in source and binary forms, with or without
5 // modification, are permitted provided that the following conditions are
6 // met:
7 //
8 // * Redistributions of source code must retain the above copyright
9 // notice, this list of conditions and the following disclaimer.
10 // * Redistributions in binary form must reproduce the above
11 // copyright notice, this list of conditions and the following disclaimer
12 // in the documentation and/or other materials provided with the
13 // distribution.
14 // * Neither the name of Google Inc. nor the names of its
15 // contributors may be used to endorse or promote products derived from
16 // this software without specific prior written permission.
17 //
18 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
19 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
20 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
21 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
22 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
23 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
24 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
25 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
26 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
27 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
28 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 //
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_
PreCalculatedPrimeTable
Definition: prime_tables.h:80
PrimeTable
Definition: prime_tables.h:43
OnTheFlyPrimeTable
Definition: prime_tables.h:56