121 lines
3.8 KiB
C++
121 lines
3.8 KiB
C++
// Copyright 2008 Google Inc.
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// All Rights Reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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//
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following disclaimer
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// in the documentation and/or other materials provided with the
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// distribution.
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// * Neither the name of Google Inc. nor the names of its
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// contributors may be used to endorse or promote products derived from
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// this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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//
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// Author: wan@google.com (Zhanyong Wan)
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// Author: vladl@google.com (Vlad Losev)
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// This provides interface PrimeTable that determines whether a number is a
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// prime and determines a next prime number. This interface is used
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// in Google Test samples demonstrating use of parameterized tests.
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#ifndef GTEST_SAMPLES_PRIME_TABLES_H_
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#define GTEST_SAMPLES_PRIME_TABLES_H_
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#include <algorithm>
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// The prime table interface.
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class PrimeTable {
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public:
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virtual ~PrimeTable() {}
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// Returns true iff n is a prime number.
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virtual bool IsPrime(int n) const = 0;
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// Returns the smallest prime number greater than p; or returns -1
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// if the next prime is beyond the capacity of the table.
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virtual int GetNextPrime(int p) const = 0;
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};
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// Implementation #1 calculates the primes on-the-fly.
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class OnTheFlyPrimeTable : public PrimeTable {
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public:
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virtual bool IsPrime(int n) const {
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if (n <= 1) return false;
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for (int i = 2; i*i <= n; i++) {
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// n is divisible by an integer other than 1 and itself.
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if ((n % i) == 0) return false;
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}
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return true;
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}
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virtual int GetNextPrime(int p) const {
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for (int n = p + 1; n > 0; n++) {
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if (IsPrime(n)) return n;
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}
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return -1;
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}
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};
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// Implementation #2 pre-calculates the primes and stores the result
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// in an array.
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class PreCalculatedPrimeTable : public PrimeTable {
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public:
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// 'max' specifies the maximum number the prime table holds.
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explicit PreCalculatedPrimeTable(int max)
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: is_prime_size_(max + 1), is_prime_(new bool[max + 1]) {
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CalculatePrimesUpTo(max);
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}
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virtual ~PreCalculatedPrimeTable() { delete[] is_prime_; }
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virtual bool IsPrime(int n) const {
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return 0 <= n && n < is_prime_size_ && is_prime_[n];
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}
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virtual int GetNextPrime(int p) const {
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for (int n = p + 1; n < is_prime_size_; n++) {
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if (is_prime_[n]) return n;
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}
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return -1;
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}
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private:
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void CalculatePrimesUpTo(int max) {
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::std::fill(is_prime_, is_prime_ + is_prime_size_, true);
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is_prime_[0] = is_prime_[1] = false;
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for (int i = 2; i <= max; i++) {
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if (!is_prime_[i]) continue;
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// Marks all multiples of i (except i itself) as non-prime.
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for (int j = 2*i; j <= max; j += i) {
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is_prime_[j] = false;
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}
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}
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}
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const int is_prime_size_;
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bool* const is_prime_;
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};
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#endif // GTEST_SAMPLES_PRIME_TABLES_H_
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