Implementation of Eratosthenes (Eratosthenes) prime sieve parallelization using OpenMP

1. Algorithm Introduction 1.1 Sieve Method origin

Sieve method is a simple algorithm for verifying prime numbers. It is said that the ancient Greek Eratosthenes (Eratosthenes, about 274-194 BC) invented, also known as Eratosthenes sieve method (Sieve of Eratosthenes).

1.2 Sieve Process

the specific approach is:Give the range n to sieve the values to find out n √ The prime number within the P1,P2,P3,......,PK. From the smallest prime number 2 to sift, that is, 2 left, the multiples of 2 are removed, and then the next prime, that is, 3 sieve, 3 left, the multiples of 3 were removed; then the next prime number 5 sieve, 5 left, the multiples of 5 are removed;

2. Implementing the Code

The code is a Linux platform and can be easily modified to be ported to Windows. using OpenMP to achieve simple parallel acceleration, the use of OpenMP, Baidu Search "OpenMP simple tutorial."

#include <cmath>#include <cstdlib>#include <cstring>#include <cstdio>#include <iostream>#include <sys/time.h>#include <cassert>#include <omp.h>using namespace STD;typedef unsigned intUInt32;typedef unsigned Long Long intUInt64;inline voidSieve (UInt64 start,uint64 end,uint64& num,intThreadnum) {assert (start>1);BOOL* A =New BOOL[end+1];memset(A +2,true, end+1);#pragma omp parallel for num_threads (threadnum)   for(UInt64 i =2; I <= (UInt64)sqrt(end); i++) {if(A[i]) for(UInt64 j = i; i*j <= end; j + +) A[i*j] =false; } UInt64 prime_num=0;if(start==2) prime_num++;#pragma omp parallel for num_threads (threadnum) reduction (+: Prime_num)   for(UInt64 i = (start%2==0? start+1: start); I <=end; i + =2)  {if(A[i]) prime_num++; } Num=prime_num;Delete[] A;}intMainintargcChar* argv[]) {if(argc!=4){fprintf(stderr,"Usage:eratosthenes start_number end_number threadnum\n");Exit(-1); }structTimeval Ts,te; UInt64 Start=atoi (argv[1]); UInt64 End=atoi (argv[2]);intThreadnum=atoi (argv[3]); UInt64 num=0;    Gettimeofday (&ts,null);    Sieve (Start,end,num,threadnum); Gettimeofday (&te,null);cout<<"Count:"<<num<<endl;cout<<"Total time:"<< ((te.tv_sec-ts.tv_sec) * ++ (TE.TV_USEC-TS.TV_USEC)/ +) <<"MS"<<endl; GetChar ();return 0;}

Reference documents

[1] Baidu Encyclopedia-sieve Method

Implementation of Eratosthenes (Eratosthenes) prime sieve parallelization using OpenMP