Example 2-2. bigfact

  #!/usr/bin/perl
  # bigfact - calculate prime factors
  use strict;
  use integer;
  
  our ($opt_b, $opt_d);
  use Getopt::Std;
  
  @ARGV && getopts('bd')        or die "usage: $0 [-b] number ...";
  
  load_biglib( ) if $opt_b;
  
  ARG: foreach my $orig ( @ARGV ) {
      my ($n, %factors, $factor);
      $n = $opt_b ? Math::BigInt->new($orig) : $orig;
      if ($n + 0 ne $n) { # don't use -w for this
          printf STDERR "bigfact: %s would become %s\n", $n, $n+0 if $opt_d;
          load_biglib( );
          $n = Math::BigInt->new($orig);
      }
      printf "%-10s ", $n;
  
      # Here $sqi will be the square of $i. We will take advantage
      # of the fact that ($i + 1) ** 2 =  = $i ** 2 + 2 * $i + 1.
      for (my ($i, $sqi) = (2, 4); $sqi <= $n; $sqi += 2 * $i ++ + 1) {
          while ($n % $i =  = 0) {
              $n /= $i;
              print STDERR "<$i>" if $opt_d;
              $factors {$i} ++;
          }
      }
  
      if ($n != 1 && $n != $orig) { $factors{$n}++ }
      if (! %factors) {
          print "PRIME\n";
          next ARG;
      }
      for $factor ( sort { $a <=> $b } keys %factors ) {
          print "$factor";
          if ($factors{$factor} > 1) {
              print "**$factors{$factor}";
          }
          print " ";
      }
      print "\n";
  }
  
  # this simulates a use, but at runtime
  sub load_biglib {
      require Math::BigInt;
      Math::BigInt->import( );          #immaterial?
  }