use Math::BigInt;
use bigint;
use strict;
use warnings;

sub convert_bitstring_to_number
{
  my $bitstring = shift;
  my $h = unpack( 'H*', $bitstring );
  my $bh = new Math::BigInt '0x'.$h;
  $bh->as_int;
}
[download]

This can be generalised for other orderings of the bytes, and of the bits in each byte, of the bitstring. Four types of bitstring can be identified:

1. big-endian: ms-bit of first byte is the ms-bit of the multi-byte number. This is handled as shown, ie:

     my $h = unpack( 'H*', $bitstring ) ;
   [download]

2. little-endian: ls-bit of first byte is the ls-bit of the multi-byte number. This is handled:

     my $h = unpack( 'H*', scalar reverse $bitstring ) ;
   [download]

   Note that this is the same order as vec($v, $b, 1)

3. big-endian reversed bytes: ls-bit of first byte is the ms-bit of the multi-byte number. This is handled:

     my $h = unpack( 'H*', pack('b*', unpack('B*', $bitstring)) ) ;
   [download]

4. little-endian reversed bytes: ms-bit of first byte is the ls-bit of the multi-byte number. This is handled:

     my $h = unpack( 'H*', pack('b*', unpack('B*', scalar reverse $bitstr
   +ing)) ) ;
   [download]