use Perl

• On the other hand... (Score:1)

  by pjm (639) on 2003.10.03 5:51 (#24644)

  Colour me naive, (close relative of mauve I guess), but a warped kind of opposite to this happened to me this afternoon. Not in the sense of finding a numberical routine that ran x-million times faster in perl, but in being shocked at how fast perl could rip through some arithmetic.
  
  I'm teaching a course that touches on crypto, and the intro lecture mentions Hill's cipher in 2x2 form. (2x2 matrices with elemnents in Z_26, say 0..25.) I wondered just what proportion of matrices would be invertible mod 26, and threw an ugly script at it...
  
  #!/local/bin/perl58 -w
  use strict;
  my $ok;
  my $total;
  foreach my $i (0..25){
          print "Motoring through \$i=$i now\n";
          foreach my $j (0..25){
                  foreach my $k (0..25){
                          foreach my $l (0..25){
                                  $total++;
                                  my $det=$i*$l-$j*$k;
                                  if ($det%2 && $det%13){$ok++;}
                          }
                  }
          }
  }
  print "$ok okay out of a total of $total\n";
  
  The "motoring through..." print statement shows my lack of confidence in this finishing in real time, but much to my amazement in about a second we had...
  
  Motoring through $i=0 now
  [...]
  Motoring through $i=25 now
  157248 okay out of a total of 456976
  
  Admittedly this is on a pretty zappy Sun box: it was about 10 times slower on my humble 400MHz imac. But still not too shabby. I 'spose anyone reading this is thinking: "and how did the C version go?". Mumble, mumble... me no do C... how hard can it be given the C-ish nature of the above? OK, at the very real risk of severe embarrassment.
  
  int main(){
  int $ok=0;
  int $total=0;
  int $det=0;
  int $i,$j,$k,$l;
  for ($i=0;$i26;$i++){
          printf("Motoring through $i=%d now\n",$i);
          for ($j=0;$j26;$j++){
                  for ($k=0;$k26;$k++){
                          for ($l=0;$l26;$l++){
                                  $total++;
                                  $det=$i*$l-$j*$k;
                                  if (($det%2) && ($det%13))
                                        $ok++;
                          }
                  }
          }
  }
  printf("%d okay out of a total of %d\n", $ok,$total);
  }
  
  157248 okay out of a total of 456976
  
  Yay: it works. And yep, it's *fast*. Pretty much makes the imac look like the Sun running perl and the Sun running C look like greased lightning.
  
  Cheers,
  Paul

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