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/*
*
* compile: clang++ -march=native -mtune=native -Ofast -std=c++17 PrimeCPP.cpp -o Primes_clang++.exe
*
*/
#include <chrono>
#include <ctime>
#include <iostream>
#include <fstream>
#include <bitset>
#include <map>
#include <cstring>
#include <cmath>
using namespace std;
using namespace std::chrono;
// array of bits initially set all to 1's and then selectively set to false as each composite (non prime number) gets market
class BitArray {
uint32_t *array;
size_t arrSize;
inline static size_t arraySize(size_t size) {
return (size >> 5) + ((size & 31) > 0);
}
inline static size_t index(size_t n) {
return (n >> 5);
}
inline static uint32_t getSubindex(size_t n, uint32_t d) {
return d & uint32_t(uint32_t(0x01) << (n % 32));
}
inline void setFalseSubindex(size_t n, uint32_t &d) {
d &= ~uint32_t(uint32_t(0x01) << (n % (8*sizeof(uint32_t))));
}
public:
explicit BitArray(size_t size) : arrSize(size) {
array = new uint32_t[arraySize(size)];
std::memset(array, 0xFF, (size >> 3) + ((size & 7) > 0));
}
~BitArray() {delete [] array;}
bool get(size_t n) const {
return getSubindex(n, array[index(n)]);
}
void set(size_t n) {
setFalseSubindex(n, array[index(n)]);
}
};
class prime_sieve
{
private:
long sieveSize = 0;
long primeCount = 0;
BitArray Bits;
public:
prime_sieve(long long n)
: Bits(n), sieveSize(n)
{
}
~prime_sieve()
{
}
void runSieve(std::chrono::time_point<std::chrono::steady_clock> tStart)
{
int prime = 2;
int q = (int) sqrt(sieveSize);
while (prime <= q)
{
for (int num = prime; num < sieveSize; num++)
{
if (Bits.get(num))
{
prime = num;
this->primeCount++;
// mark all composites
for (int comp = prime * 2; comp < sieveSize; comp += prime)
Bits.set(comp);
}
}
}
auto duration = duration_cast<microseconds>(steady_clock::now() - tStart).count() / 1000000.0;
printf("Time: %lf, Limit: %ld, Primes Found: %ld\n", duration, this->sieveSize, this->primeCount);
}
void writeResults(void)
{
std::ofstream outfile("primes.txt", std::ios::out);
if (outfile.is_open())
{
outfile << "2, ";
int count = (sieveSize >= 2); // Starting count (2 is prime)
for (int num = 3; num <= sieveSize; num+=2)
{
if (Bits.get(num))
outfile << num << ", ";
}
outfile << std::endl;
outfile.close();
}
else
std::cout << "Unable to open a file for writing" << std::endl;
}
};
int main()
{
auto tStart = steady_clock::now();
prime_sieve sieve(1000000000LL);
sieve.runSieve(tStart);
sieve.writeResults();
}
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