Translation of someone elses code for a more sophisticated prime sieve

genprimes2.c

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

int main(int argc, char** argv)
{
	if (argc != 2) {
		printf("usage: genprimes2 num\n");
		return 0;
	}

	int limit = atoi(argv[1]);
	if (limit < 10) {
		printf("the upper bound must be at least 10\n");
		return 0;
	}

	int sieveBound = floor((limit-1)/2.0);
	char *sieve = (char*)calloc(sizeof(char), sieveBound+1);
	int crossLimit = floor((floor(sqrt(limit))-1)/2.0);

	int i, j;
	for (i = 1; i <= crossLimit; i++) {
		if (sieve[i]) {
			continue;
		}

		for (j = 2*i*(i+1); j < sieveBound+1; j += 2*i+1) {
			sieve[j] = 1;
		}
	}

	printf("2\n");
	for (i = 1; i <= sieveBound; i++) {
		if (!sieve[i]) {
			printf("%d\n", 2*i+1);
		}
	}

	return 0;
}