In description of unpack there is following method to count number of bits: 
# Count the bits in a chunk of memory (e.g. a select vector)
unpack( '%32b*', $mask );

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 Update: sorry, I misunderstood question. If you have string of bits with one bit set, then you could try just $bitstring =~ /1(0*)$/; $originalvalue = length($1)+1;

In reply to Re: Which bit is set? (inverse of (1<<$value) operator) by grizzley
in thread Which bit is set? (inverse of (1<<$value) operator) by wirito

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