cf-evaluate

#!/usr/bin/perl
#

@ARGV or usage();

my $x = [0, 1, 1, 0];

sub input {
  my ($x, $p) = @_;
  my ($a, $b, $c, $d) = @$x;
  [ $b, $a + $b*$p, $d, $c + $d*$p ];
}

sub val {
  my $x = shift;
  my ($a, $b, $c, $d) = @$x;
  return [$b, $d];
}

for (@ARGV) {
  $x = input($x, $_);
  my $f = val($x);
  printf "%8d / %8d   %20.20f\n", @$f, $f->[1] &&  $f->[0] / $f->[1];
}

sub usage {
  print qq{Usage: $0 a1 a2 a3 ...
The a_i are the partial quotients of a simple continued fraction.
The program will print out the convergents.
};
  exit 1;
}