primesingle.cpp

求某范围内得素数

///////////////////////////////////////////////////////////////////////////////
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///////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////
//
//  This implments a brute force method of determining the prime numbers
//  in a given range 1..n.
//
///////////////////////////////////////////////////////////////////////////////
#include <stdio.h>
#include <windows.h>
#include <time.h>
#include <math.h>
static       int gProgress    = 0,
                 gPrimesFound = 0;
long             globalPrimes[1000000];
int              CLstart, CLend;


///////////////////////////////////////////////////////////////////////////////
//
//  GetCommandLineArguments
//
//  Grabs the number of threads from the commandline
//
///////////////////////////////////////////////////////////////////////////////
void GetCommandLineArguments(int argc, char **argv, int &start, int &end)
{
    if( argc == 3 )
    {
        CLstart = atoi(argv[1]);
        CLend   = atoi(argv[2]);
    }
    else
    {
        printf("Usage:- %s <start range> <end range>\n", argv[0]);
        exit(-1);
    }
	if (CLstart > CLend) {
		printf("Start value must be less than or equal to end\n");
		exit(-1);
	}
	if (CLstart < 1 && CLend < 2) {
		printf("Range must be positive integers\n");
		exit(-1);
	}
	start = CLstart;
	end = CLend;
	if (CLstart < 2) start = 2;
	if (start <= 2) globalPrimes[gPrimesFound++] = 2;

}

void ShowProgress( int val, int range )
{
    int percentDone = 0;

    gProgress++;

    percentDone = (int)((float)gProgress/(float)range *200.0f + 0.5f);

	if( percentDone % 10 == 0 ) 
        printf("\b\b\b\b%3d%%", percentDone);
	
}

bool TestForPrime(int val)
{
    int limit, factor = 3;

    limit = (long)(sqrtf((float)val)+0.5f);
    while( (factor <= limit) && (val % factor))
        factor ++;

    return (factor > limit);
}

void FindPrimes(int start, int end)
{
    // start is always odd
    int range = end - start + 1; 

    for( int i = start; i <= end; i += 2 )
    {
        if( TestForPrime(i) )
            globalPrimes[gPrimesFound++] = i;
        
        ShowProgress(i, range);
    }
}

int main(int argc, char **argv)
{
	int     start, end;
    clock_t before, after;

    GetCommandLineArguments(argc, argv, start, end);

    if((start % 2) == 0 )
        start = start + 1;  // ensure we start with an odd number

    before = clock();
    FindPrimes(start, end);
    after = clock();


    printf("\n\n%8d primes found between %6d and %6d in %7.2f secs\n",
           gPrimesFound,
           CLstart, CLend, (float)(after - before)/ CLOCKS_PER_SEC);
}