comment on

merlyn wrote an interesting column that uses the classic Sieve of Eratosthenes for finding primes. It includes clever use of the vec operator. Omitting the print it finds all primes below 1 million in 10 seconds on a mediocre i386:

$ time perl -w
use strict;
my $UPPER = 1_000_000;
my $sieve = "";
GUESS: for (my $guess = 2; $guess <= $UPPER; $guess++) {
  next GUESS if vec($sieve,$guess,1);
  #print "$guess\n";
  for (my $mults = $guess * $guess; $mults <= $UPPER; $mults += $guess
+) {
    vec($sieve,$mults,1) = 1;
  }
}
__END__

real    0m10.003s
user    0m2.191s
sys     0m0.003s
[download]

There's an interesting animation here that shows how the algorithm works.

See also Math::Prime::XS.

--
Andreas

In reply to Re: To Findout Prime number by andreas1234567
in thread To Findout Prime number by babug_prg

Are you posting in the right place? Check out Where do I post X? to know for sure.
Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
<code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
Want more info? How to link or How to display code and escape characters are good places to start.


There's more than one way to do things
	PerlMonks