#!/usr/bin/env perl
use strict;
use warnings;
# Overkill, but let's try to select a good bigint module.
my $bigint_class;
if (eval { require Math::GMPz; 1; }) {
$bigint_class = "Math::GMPz";
} elsif (eval { require Math::GMP; 1; }) {
$bigint_class = "Math::GMP";
} else {
require Math::BigInt;
Math::BigInt->import(try=>"GMP,Pari");
$bigint_class = "Math::BigInt";
}
use Math::Prime::Util ':all';
use Time::HiRes qw(gettimeofday tv_interval);
$| = 1;
my $time_start = [gettimeofday];
prime_precalc(1_000_000);
{
my @fibstate;
my $nth = 1;
my $n = 0;
while (1) {
# Exploit knowledge that excepting k=4, all prime F_k have a prime k.
my $k = ($nth <= 2) ? 2 + $nth : nth_prime($nth);
$nth++;
my $Fk = fib_n($k, \@fibstate);
if (is_prob_prime($Fk)) {
my $time_int = tv_interval($time_start);
printf "%3d %7d %20.5f\n", ++$n, $k, $time_int;
}
}
}
sub fib_n {
my ($n, $fibstate) = @_;
@$fibstate = (1, $bigint_class->new(0), $bigint_class->new(1))
unless defined $fibstate->[0];
my ($curn, $a, $b) = @$fibstate;
die "fib_n only increases" if $n < $curn;
do { ($a, $b) = ($b, $a+$b); } for (1 .. $n-$curn);
@$fibstate = ($n, $a, $b);
$b;
}