#!/usr/bin/perl -w
use strict;

print "power of 2 bit of 1 is: ",MSbit(1),"\n"; #prints 0
print "power of 2 bit of 8 is: ",MSbit(8),"\n"; #prints 3

my $num = 256;
print "power of 2 bit of $num is: ",MSbit($num),"\n"; #prints 8

$num = $num << 1;
print "power of 2 bit of $num is: ",MSbit($num),"\n"; #prints 9

$num = 254;
print "power of 2 bit of $num is: ",MSbit($num),"\n"; #prints 7
$num = $num << 1;
print "power of 2 bit of $num is: ",MSbit($num),"\n"; #prints 8

#Most Significant bit numbering is like
#...9876543210
#
sub MSbit  ##returns power of 2 of MS bit
{
   my $num = shift;
   die "illegal value in MSbit" if $num == 0;
   my $bit =-1;
   while ($num != 0)
   {
      $num = $num >> 1;
      $bit++;
   }
   return $bit;
}

__END__
output of above is:
power of 2 bit of 1 is: 0
power of 2 bit of 8 is: 3
power of 2 bit of 256 is: 8
power of 2 bit of 512 is: 9
power of 2 bit of 254 is: 7
power of 2 bit of 508 is: 8