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prime_tables.h
// Copyright 2008 Google Inc.
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// Author: wan@google.com (Zhanyong Wan)
// Author: vladl@google.com (Vlad Losev)
// This provides interface PrimeTable that determines whether a number is a
// prime and determines a next prime number. This interface is used
// in Google Test samples demonstrating use of parameterized tests.
#ifndef GTEST_SAMPLES_PRIME_TABLES_H_
#define GTEST_SAMPLES_PRIME_TABLES_H_
#include <algorithm>
// The prime table interface.
class PrimeTable {
public:
virtual ~PrimeTable() {}
// Returns true iff n is a prime number.
virtual bool IsPrime(int n) const = 0;
// Returns the smallest prime number greater than p; or returns -1
// if the next prime is beyond the capacity of the table.
virtual int GetNextPrime(int p) const = 0;
};
// Implementation #1 calculates the primes on-the-fly.
class OnTheFlyPrimeTable : public PrimeTable {
public:
virtual bool IsPrime(int n) const {
if (n <= 1) return false;
for (int i = 2; i*i <= n; i++) {
// n is divisible by an integer other than 1 and itself.
if ((n % i) == 0) return false;
}
return true;
}
virtual int GetNextPrime(int p) const {
for (int n = p + 1; n > 0; n++) {
if (IsPrime(n)) return n;
}
return -1;
}
};
// Implementation #2 pre-calculates the primes and stores the result
// in an array.
class PreCalculatedPrimeTable : public PrimeTable {
public:
// 'max' specifies the maximum number the prime table holds.
explicit PreCalculatedPrimeTable(int max)
: is_prime_size_(max + 1), is_prime_(new bool[max + 1]) {
CalculatePrimesUpTo(max);
}
virtual ~PreCalculatedPrimeTable() { delete[] is_prime_; }
virtual bool IsPrime(int n) const {
return 0 <= n && n < is_prime_size_ && is_prime_[n];
}
virtual int GetNextPrime(int p) const {
for (int n = p + 1; n < is_prime_size_; n++) {
if (is_prime_[n]) return n;
}
return -1;
}
private:
void CalculatePrimesUpTo(int max) {
::std::fill(is_prime_, is_prime_ + is_prime_size_, true);
is_prime_[0] = is_prime_[1] = false;
for (int i = 2; i <= max; i++) {
if (!is_prime_[i]) continue;
// Marks all multiples of i (except i itself) as non-prime.
for (int j = 2*i; j <= max; j += i) {
is_prime_[j] = false;
}
}
}
const int is_prime_size_;
bool* const is_prime_;
// Disables compiler warning "assignment operator could not be generated."
void operator=(const PreCalculatedPrimeTable& rhs);
};
#endif // GTEST_SAMPLES_PRIME_TABLES_H_
PreCalculatedPrimeTable
Definition: prime_tables.h:80
PrimeTable
Definition: prime_tables.h:43
OnTheFlyPrimeTable
Definition: prime_tables.h:56