#!/usr/local/bin/perl -w
#
$limit = shift or die "No limit supplied\n";
die "Limit is not integer\n" unless $limit =~ /^\d+$/;
$sqrtLimit = sqrt $limit;
$sieve = "";
vec($sieve, 0, 1) = 1;
vec($sieve, 1, 1) = 1;
vec($sieve, $limit, 1) = 0;
$reached = 1;
while($reached < $sqrtLimit)
{
    $prime = $reached + 1;
    ++ $prime while vec($sieve, $prime, 1);
    print "$prime is a prime\n";
    $fill = 2 * $prime;
    while($fill <= $limit)
    {
        vec($sieve, $fill, 1) = 1;
	$fill += $prime;
    }
    $reached = $prime;
}
foreach $value ($reached + 1 .. $limit)
{
    print "$value is a prime\n" unless vec($sieve, $value, 1);
}