sub bits_needed {
    my ( $unsigned, $resolution ) = @_;
    my $bits_needed = floor( log2( $unsigned ) ) + 1;
    $bits_needed += $resolution - $bits_needed % $resolution
        if defined $resolution;
    return $bits_needed;
}

##</code><code>##

sub log2 {
    my $n = shift;
    return log($n)/log(2);
}

##</code><code>##


use strict;
use warnings;
use Bit::Vector;
use Text::Template;
use v5.12;


my $orig_hex = "6bf";
my ( $reverse, $details ) = hex_reverse_bitwise( $orig_hex, 12 );


print Text::Template->fill_this_in(
    do{ undef $/; <DATA> }, HASH => $details,
);



# Return bitwise reversed hex digits in scalar context.
# In list context, return reversed hex digits plus a hashref
# containing more detailed analysis.

sub hex_reverse_bitwise {
    my ( $start, $bit_size ) = @_;

    my $orig_vec = Bit::Vector->new_Hex( $bit_size, $orig_hex );
    my $rev_vec = Bit::Vector->new( $bit_size );

    $rev_vec->Reverse( $orig_vec );
    my $reversed = $rev_vec->to_Hex;

    return( 
        $reversed, 
        wantarray() ? {
            orig_hex        => $orig_hex,
            orig_bits       => $orig_vec->to_Bin,
            reversed_bits   => $rev_vec->to_Bin,
            new_hex         => $reversed,
        } : () 
    );
}



__DATA__

Given the hex digits '{lc $orig_hex}' with a bit
representation of '{$orig_bits}',
reversing the bits to '{$reversed_bits}' we get
a hex representation of '{lc $new_hex}'.



##</code><code>##


Given the hex digits '6bf' with a bit
representation of '011010111111',
reversing the bits to '111111010110' we get
a hex representation of 'fd6'.