sieve.c

来自「著名的Parser库Spirit在VC6上的Port」· C语言 代码 · 共 37 行

/* -*- mode: c -*-
 * $Id: Sieve.c,v 1.3 2001/10/20 15:43:19 nuffer Exp $
 * http://www.bagley.org/~doug/shootout/
 */

/*
#include <stdio.h>
#include <stdlib.h>
*/

int
main(int argc, char *argv[]) {
    int NUM = ((argc == 2) ? atoi(argv[1]) : 1);
    static char flags[8192 + 1];
    long i, k;
    int count = 0;

    while (NUM--) {
	count = 0; 
	for (i=2; i <= 8192; i++) {
	    flags[i] = 1;
	}
	for (i=2; i <= 8192; i++) {
	    if (flags[i]) {
		// remove all multiples of prime: i
		for (k=i+i; k <= 8192; k+=i) {
		    flags[k] = 0;
		}
		count++;
	    }
	}
    }
    printf("Count: %d\n", count);
    return(0);
}