I'm after the positions of the set bits

Ah so sorry, I left that as an exercise for the reader. All you have to do is run through the array of 0,1 values, and push the offset to another array if the value is 1. Then return that array. Which goes something like (untested)

sub set_bit_offsets {
    my @bitmap = split //, unpack('b*', @_);
    my @offset;
    for my $off (0..$#bitmap) {
        if ($bitmap[$off] == 1) {
            push @offset, $off;
        }
    }
    return @offset;
}

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In terms of efficiency, yes, that could be written as a one-liner. That would be something like:

sub set_bit_offsets {
    my @bitmap = split //, unpack('b*', @_);
    return grep {$bitmap[$_]} 0..$#bitmap;
}

[download]

• another intruder with the mooring in the heart of the Perl

In reply to Re^3: bit pattern to bit position mapping by grinder
in thread bit pattern to bit position mapping by Anonymous Monk

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