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Efficient bit counting with a twist.by BrowserUk (Pope)
|on Jan 27, 2013 at 06:22 UTC||Need Help??|
BrowserUk has asked for the wisdom of the Perl Monks concerning the following question:
Given a bit vector $v, this: my $c = unpack '%32b*', $v; will count the set bits very efficiently.
However, I need to count the set bits preceding (not including) a given bit position within $v.
I can do that using:
But that is grossly inefficient for large vectors.
Can you do it more efficiently?
Note:The rest of the code is pure perl, so I'd rather avoid going to XS to do this if possible.
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