Misread :( 

my %lookup = map { $_ => 1 << (ord($_) - ord('A')) } 'A'..'Z';

my $c = 'ABCHI';

my $bitmap = 0;
$bitmap |= $lookup{$_} for $c =~ /(.)/g;

print('A'..'Z', "\n");
print(scalar(reverse(sprintf("%26b", $bitmap))), "\n");

[download]

outputs 

ABCDEFGHIJKLMNOPQRSTUVWXYZ
111000011

[download]

Update: Array version: 

my @powers = map { 1 << $_ } 0..25;

my $c = 'ABCHI';

my $bitmap = 0;
$bitmap |= $powers[ord($_)-ord('A')] for $c =~ /(.)/g;

print('A'..'Z', "\n");
print(scalar(reverse(sprintf("%26b", $bitmap))), "\n");

[download]

Update: Replaced += with |=. It makes it tolerant to repeated letters.

In reply to Re: Algorithm to convert combinations to bitstring by ikegami
in thread Algorithm to convert combinations to bitstring by Limbic~Region

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