C:\test>type CIDRtest.pl
#! perl -slw
use strict;
use integer;

for my $n ( 0 .. 31 ) {
    my $addr = (1 << $n) + 1;
    printf "\r%u", $addr;
    my $nbits = 32;
    while( 1 ) {
        my $bit = ( $addr & 0x80000000 ) >> 31;
        die "$addr -> $bit" if $bit != 0 and $bit != 1;
        $addr <<= 1;
        last unless --$nbits;
    }
}

C:\test>CIDRtest.pl
2147483649

C:\test>\perl32\bin\perl.exe CIDRtest.pl
-2147483648 -> -1 at CIDRtest.pl line 11.
2