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Using it to count set bits in the whole bytes before your position and then, if necessary, those bits in the partial byte up to but not including it via a mask might be viable.

Yes. That works and is the same scheme questor came up with (rather more compactly:) in Re: Efficient bit counting with a twist..

But the best answer is the one AnomalousMonk pointed out in Re: Efficient bit counting with a twist..

Ie. To recognise that the unpack template '%32b*' is not a indivisible token saying 'count the bits', but actually contains 3 parts:

  1. %32 accumulate a 32-bit count ...
  2. b of the binary bits set ...
  3. * for all the bits in the string.

And that by simply interpolating $p into the template, in place of *, it counts the set bits within the first $p bits of the string.

Perl had the problem solved; I just didn't recognise it :) (Hence my: D'oh! D'oh! D'oh!..... moment. :)


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In reply to Re^2: Efficient bit counting with a twist. by BrowserUk
in thread Efficient bit counting with a twist. by BrowserUk

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