my $firstbit = ($longsize * 8) - 1;
my $firstbit_mask = 1 << $firstbit;

##</code><code>##

use constant NUM_BITS = $Config{ivsize} * 8;
use constant SIGN_BIT = 1 << ( NUM_BITS - 1 );
use constant ALL_BITS = -1;

sub sr_signed {
   my ($p, $q) = @_;
   if ($p & SIGN_BIT) {
      return ($p >> $q) | ($ALL_BITS << (NUM_BITS - $q));
   } else {
      return $p >> $q;
   }
}

##</code><code>##

Shift 10101111...10101100 by 3

     10101111...10101100 >> 3
     ||||||||   |||||
      \\\\\\\\   \\\\\
       \\\\\\\\   \\\\\
        ||||||||   |||||
     00010101111...10101

     11111111...11111111 << (NUM_BITS-3)
                     |||
       _____________///
      ///
     |||
     11100000...00000000

     00010101111...10101
   | 11100000...00000000
     -------------------
     11110101111...10101