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

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