sub is_fibonnacci {
my $plus = (5 * $_[0] * $_[0]) + 4;
my $mins = (5 * $_[0] * $_[0]) - 4;
return is_perfect_square($plus) | is_perfect_square($mins);
}
No need to calculate 5 * $_[0] * $_[0] twice, and you probably meant to use the logical or operator instead of the bit-wise or operator.
sub is_fibonnacci {
my $plus = (5 * $_[0] * $_[0]) + 4;
my $mins = $plus - 8;
return is_perfect_square($plus) || is_perfect_square($mins);
}
(The logical operators short-circuit so is_perfect_square($mins) will only execute if is_perfect_square($plus) is true.)
sub is_perfect_square {
my $sqrt = int(sqrt($_[0]));
return $sqrt * $sqrt == $_[0];
}
Or just:
sub is_perfect_square { int( $_[0] ** .5 ) ** 2 == $_[0] }