primes/primes.sieve.c

#include <stdlib.h>
#include <stdio.h>
#include <math.h>

int *SieveArray;

void InitSieve(unsigned int Max)
{
	unsigned int i;
	for (i=0; i <= Max; i++)
	{
		SieveArray[i] = 1;
	}
}

void Sieve(unsigned int Max)
{
	unsigned int i,j;
	unsigned int low_max = sqrt(Max);
	for( i = 2; i <= low_max; i++)
	{
		for ( j = i*2; j <= Max; j += i)
		{
			SieveArray[j] = 0;
		}
	}
}

void ShowResults(unsigned int Max)
{
	unsigned int i;
	for (i =3; i <= Max; i++) 
	{
		if (SieveArray[i])
		{
			printf("%d\n", i);
		}
	}
}

int main(int argc ,char **argv)
{
	unsigned int Max;
	
	if(argc < 2) {
		printf("primes.sieve.c <Max>\n");
		return 1;
	} else {
		Max = atoi(argv[1]);
	}
	
	if(Max < 1)
	{
		printf("Invalid Max specified\n");
		return 1;
	}

	SieveArray = (int*) malloc(sizeof(int)*Max);
	if(!SieveArray) 
	{
		printf("Error: could not allocate SieveArray at Max:%d\n", Max);
		return 1;
	}
	
	InitSieve(Max);
	Sieve(Max);
	ShowResults(Max);

	free(SieveArray);
	
	return 0;
}