coreutils/src/wheel-gen.pl

#!/usr/bin/perl -w
# -*- perl -*-

eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
    if 0;

use strict;
(my $program_name = $0) =~ s|.*/||;

sub END
{
  use POSIX qw (_exit);
  # This is required if the code might send any output to stdout
  # E.g., even --version or --help.  So it's best to do it unconditionally.
  close STDOUT
    or (warn "$program_name: closing standard output: $!\n"), _exit (1);
}

sub is_prime ($)
{
  my ($n) = @_;
  use integer;

  $n == 2
    and return 1;

  my $d = 2;
  my $w = 1;
  while (1)
    {
      my $q = $n / $d;
      $n == $q * $d
        and return 0;
      $d += $w;
      $q < $d
	and last;
      $w = 2;
    }
  return 1;
}

{
  @ARGV == 1
    or die "$program_name: missing argument\n";

  my $wheel_size = $ARGV[0];

  my @primes = (2);
  my $product = $primes[0];
  my $n_primes = 1;
  for (my $i = 3; ; $i += 2)
    {
      if (is_prime $i)
	{
	  push @primes, $i;
	  $product *= $i;
	  ++$n_primes == $wheel_size
	    and last;
	}
    }

  my $ws_m1 = $wheel_size - 1;
  print <<EOF;
/* The first $ws_m1 elements correspond to the incremental offsets of the
   first $wheel_size primes (@primes).  The $wheel_size(th) element is the
   difference between that last prime and the next largest integer
   that is not a multiple of those primes.  The remaining numbers
   define the wheel.  For more information, see
   http://www.utm.edu/research/primes/glossary/WheelFactorization.html.  */
EOF

  my @increments;
  my $prev = 2;
  for (my $i = 3; ; $i += 2)
    {
      my $rel_prime = 1;
      foreach my $divisor (@primes)
	{
	  $i != $divisor && $i % $divisor == 0
	    and $rel_prime = 0;
	}

      if ($rel_prime)
	{
	  #warn $i, ' ', $i - $prev, "\n";
	  push @increments, $i - $prev;
	  $prev = $i;

	  $product + 1 < $i
	    and last;
	}
    }

  print join (",\n", @increments), "\n";

  exit 0;
}