Dear monks

I've lost count of how many times I needed a conversion from a binary string ("1101...") to a signed integer. Each time I try to think of an elegant solution and end up with brute-force math (flip bits, add 1 to compute 2s complement, then use bin2dec). The binary->unsigned conversion is (from the Cookbook):

sub bin2dec {
    return unpack("N", pack("B32", substr("0" x 32 . shift, -32)));
}

[download]

So, is there any way to apply pack/unpack magic to convert a binary string (of any length) to a signed, 2s complement integer ?

UPDATE:

Here is one solution 

# Given a lsb-first bitstring, returns
# a 2s complement signed integer 
#
sub bin2signed
{
    my $bitstr = $_[0];
    my $is_negative = 0;

    if (substr($bitstr, -1, 1) eq "1")
    {
        $bitstr =~ tr/10/01/;
        $is_negative = 1;
    }

    my $result = 0;

    for (my $i = 0; $i < length($bitstr); ++$i)
    {
        $result += substr($bitstr, $i, 1) * (2 ** $i);
    }

    if ($is_negative)
    {
        $result += 1;
        $result *= -1;
    }

    return $result;
}

[download]

In reply to signed bin2dec by spurperl

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