use strict;
use warnings;

use ntheory 0.67 ":all";
use MCE::Flow 1.831;
use MCE::Shared;

mce_open my $err_fh, '>>', \*STDERR;

my ( $name, $rng );

my %rand = (
  "drand48" => sub { int(rand(1 << 32)) },
  "ChaCha20" => sub { irand64() },
  "/dev/urandom" => sub { unpack("Q", random_bytes(8)) }
);

# Workers receive [ begin, end ] values.

MCE::Flow::init(
  max_workers => MCE::Util::get_ncpu(),
  chunk_size  => 10000,
  bounds_only => 1,
  user_begin  => sub {
    $name = MCE->user_args()->[0];
    $rng  = $rand{ $name };
  }
);

sub func {
  my ( $beg_seq, $end_seq ) = @{ $_ };
  my ( $t, $pairs, $r1, $r2 ) = ( 0, '' );

  for ( $beg_seq .. $end_seq ) {
    ( $r1, $r2 ) = ( $rng->(), $rng->() );
    if ( gcd($r1, $r2) == 1 ) {
      $pairs .= sprintf("%20s %20s\n", $r1, $r2);
      $t++;
    }
  }

  print $err_fh $pairs;

  MCE->gather($t);
}

# The user_args option is how to pass arguments.

sub cesaro {
  my ( $name ) = @_;
  print "Usage $name:\n";

  my $n   = 10 ** 5;
  my @ret = mce_flow_s { user_args => [$name] }, \&func, 0, $n - 1;
  my $t   = 0;   $t += $_ for @ret;

  printf "%8d  %0.8f\n", $n, sqrt(6 * $n / $t);
  printf "%9s %s\n\n", "Pi", Pi();
}

cesaro("/dev/urandom");


##</code><code>##

Usage /dev/urandom:
  100000  3.14168852
       Pi 3.14159265358979


##</code><code>##

 3287478503828099458 17020534165422626509
12874128583739175743 15858105624010204897
12114767169191945777  1381808520787800067
 6217235583185614040 13880267056100467759
 6095107227201871385 14484880859615821612
 6023474899938562107  6188664627301334099
 2843055836738994412  3086747352859159329
10461621510749606095   302140866635797242
11160050491040241465  8409335412227119072
 3718439936437935345  5121716120103428116

...