Qucs-core  0.0.19
prime_tables.h
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00001 // Copyright 2008 Google Inc.
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00030 // Author: wan@google.com (Zhanyong Wan)
00031 // Author: vladl@google.com (Vlad Losev)
00032 
00033 // This provides interface PrimeTable that determines whether a number is a
00034 // prime and determines a next prime number. This interface is used
00035 // in Google Test samples demonstrating use of parameterized tests.
00036 
00037 #ifndef GTEST_SAMPLES_PRIME_TABLES_H_
00038 #define GTEST_SAMPLES_PRIME_TABLES_H_
00039 
00040 #include <algorithm>
00041 
00042 // The prime table interface.
00043 class PrimeTable {
00044  public:
00045   virtual ~PrimeTable() {}
00046 
00047   // Returns true iff n is a prime number.
00048   virtual bool IsPrime(int n) const = 0;
00049 
00050   // Returns the smallest prime number greater than p; or returns -1
00051   // if the next prime is beyond the capacity of the table.
00052   virtual int GetNextPrime(int p) const = 0;
00053 };
00054 
00055 // Implementation #1 calculates the primes on-the-fly.
00056 class OnTheFlyPrimeTable : public PrimeTable {
00057  public:
00058   virtual bool IsPrime(int n) const {
00059     if (n <= 1) return false;
00060 
00061     for (int i = 2; i*i <= n; i++) {
00062       // n is divisible by an integer other than 1 and itself.
00063       if ((n % i) == 0) return false;
00064     }
00065 
00066     return true;
00067   }
00068 
00069   virtual int GetNextPrime(int p) const {
00070     for (int n = p + 1; n > 0; n++) {
00071       if (IsPrime(n)) return n;
00072     }
00073 
00074     return -1;
00075   }
00076 };
00077 
00078 // Implementation #2 pre-calculates the primes and stores the result
00079 // in an array.
00080 class PreCalculatedPrimeTable : public PrimeTable {
00081  public:
00082   // 'max' specifies the maximum number the prime table holds.
00083   explicit PreCalculatedPrimeTable(int max)
00084       : is_prime_size_(max + 1), is_prime_(new bool[max + 1]) {
00085     CalculatePrimesUpTo(max);
00086   }
00087   virtual ~PreCalculatedPrimeTable() { delete[] is_prime_; }
00088 
00089   virtual bool IsPrime(int n) const {
00090     return 0 <= n && n < is_prime_size_ && is_prime_[n];
00091   }
00092 
00093   virtual int GetNextPrime(int p) const {
00094     for (int n = p + 1; n < is_prime_size_; n++) {
00095       if (is_prime_[n]) return n;
00096     }
00097 
00098     return -1;
00099   }
00100 
00101  private:
00102   void CalculatePrimesUpTo(int max) {
00103     ::std::fill(is_prime_, is_prime_ + is_prime_size_, true);
00104     is_prime_[0] = is_prime_[1] = false;
00105 
00106     for (int i = 2; i <= max; i++) {
00107       if (!is_prime_[i]) continue;
00108 
00109       // Marks all multiples of i (except i itself) as non-prime.
00110       for (int j = 2*i; j <= max; j += i) {
00111         is_prime_[j] = false;
00112       }
00113     }
00114   }
00115 
00116   const int is_prime_size_;
00117   bool* const is_prime_;
00118 
00119   // Disables compiler warning "assignment operator could not be generated."
00120   void operator=(const PreCalculatedPrimeTable& rhs);
00121 };
00122 
00123 #endif  // GTEST_SAMPLES_PRIME_TABLES_H_