#!/usr/bin/perl -w

# LFSR - Implement arbitrary-sized linear feedback 
# shift registers

# Convert the seed from decimal to binary
$seed = dec2bin(shift);

@array = split('', $seed);

@xor_bits = @ARGV;

# Sure hope Perl always uses 32-bit ints!
splice(@array, 0, 31-$ARGV[0]);

# Let the user bang on <ENTER> until he's had his 
# fill of random bits
while (1) {       
    getc();
    $new_bit = 0 + $array[0]; # Yes, the "0 +" is necessary.
    foreach (@xor_bits[1..$#xor_bits]) {
        $new_bit ^= $array[$#array - $_];
    }
    print pop @array;
    unshift (@array, $new_bit);
}

sub dec2bin { unpack("B*", pack("N", shift)) }