UPDATE:Just in case there is anyone (else?) who hasn't spotted the joke.

Variable-length, signed binary strings DO NOT MAKE ANY SENSE!!!.

What values do the following binary strings represent?

• 0b10

  2 or -0?

• 0b11111111111111111111111111111111111111111111

  A big integer or -1?

You cannot two's complement a variable number of bits without fixing the length. Yes. This post was sacarstic and should have been identified as such, but I thought it obvious.

END UPDATE

Okay. Try this version. It will handle up to 1023 digit binary strings. Beyond that, you'll probably need Math::BigInt

sub sb2d{
    my $n=shift; 
    return undef unless $n =~ m[^[01]+$];
    my $s=ord( $n )==49;  
    $n=~tr[01][10] if $s; 
    $n = eval{ no warnings; eval '0b'.$n;};  
    $s ? -1 * ++$n : $n 
}
[download]

Update: The above is overly crude, so here is (I think) a slightly improved version. It still uses eval and requires no warnings;, but this seems to me acceptable to re-use perl's built-in binary string parser rather than role your own? It should be relatively safe unless anyone can see a way of injecting "nasty code" that uses only '0's & '1's?

sub signedBin2Dec{ 
    my $n=shift; 
    return undef unless $n =~ m[^([01])[01]+$]; 
    $n=~tr[01][10] if $1; 
    $n = do{ no warnings; eval '0b'. $n}; 
    $1 ? -1 * ++$n : $n 
}
[download]