Re: Zeckendorf representation

[jwkrahn]

in reply to Zeckendorf representation

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] }

[thmsdrew]

Thanks for your input! What do you mean by "short circuit"? Also, the difference between your is_perfect_square sub and mine is that mine is much more clear. I can afford the extra line for a bit of clarity.

[lidden]

What do you mean by "short circuit"?

It means that the part after || will only be evaluated if it is needed know the result of the operator. In the case of the or-operator the second half is redundant if the first is true, since the total will be true no matter what the second part is.

[thmsdrew]

I don't really understand how that is a problem. If the first part passes, then I want it to return true, and I truly don't care what the second part is. I guess I see how that's redundant, though.