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#! /usr/bin/env slsh
% This demo counts the number of primes between 2 and some integer
private define usage ()
{
() = fprintf (stderr, "Usage: %S <integer greater than 2>\n", __argv[0]);
exit (1);
}
define count_primes (num)
{
variable size = (num - 1)/2;
variable nonprimes = Char_Type[size + 1]; % last one is sentinel
variable count = 1;
variable prime = 3;
variable i = 0;
do
{
count++;
%()=printf ("%S\n", prime);
nonprimes [[i:size-1:prime]] = 1;
variable i_save = i;
while (i++, nonprimes[i])
;
prime += 2 * (i - i_save);
}
while (i < size);
return count;
}
private variable Num;
if (__argc != 2)
usage ();
Num = integer (__argv[1]);
if (Num < 3)
usage ();
tic ();
()=printf ("\n\n%d primes between 2 and %d in %f seconds.\n",
count_primes (Num), Num, toc ());
exit(0);
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