イテレータ修正

やっぱりお馬鹿してたわけで，pushを使えば十分な速さでした．

use strict;
use warnings;
use Time::HiRes qw/gettimeofday tv_interval/;

my $x=primefactory2();
my $sum;

my $start = [gettimeofday];
while (1){
   my $p=$x->();
   last if $p>2000000;
   $sum += $p;
}
my $end = [gettimeofday];
printf "%.6f 秒", tv_interval($start, $end);
print $sum;

sub next_cand{
    $_[0] + 2 * ($_[0] % 6 ==5) + 4*($_[0] % 6 ==1);
}

sub primefactory2{
    my @primes=(2,3,5);
    my $state=-1;
    return sub{
        $state++;
        return $primes[$state] if $state==0 or $state==1 or $state==2;
        my $prime_cand=next_cand($primes[-1]);
        my $th;
        SIEVE:
         $th = int(sqrt($prime_cand))+1;
        foreach my $d ( @primes ){
            last if $d>$th;
            if ( ($prime_cand % $d ==0)  ){
                $prime_cand = next_cand($prime_cand);
                goto SIEVE; 
            }
        }
        #@primes=(@primes,$prime_cand);
        push(@primes,$prime_cand);
        return $primes[-1];
    }
}

この結果は約12秒でした．