A bit pattern can be converted to a list of bit positions set using grep: 

bitpattern_2_indices {
    my $bit_pattern = shift;
    grep $bit_pattern & 1<<$_, 0..31;
}

my @indices = bitpattern_2_indices(12345);
print "@indices"; # prints 0 3 4 5 12 13

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Is there a more efficient way?

Can the range (0..31) be reduced by inspection?

In reply to bit pattern to bit position mapping by Anonymous Monk

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