On Sat, Oct 01, 2005 at 07:12:13PM -0700, Ben wrote: > I'm looking for a quick way to find the number of bits that are > different between two bitmasks of the same size. I'll be doing this a > lot, so speed is desirable.... some kind of indexing would be even > better. It seems like this problem must have been solved before....
Step 1: Use XOR to get the bits that are different. Step 2: Count the bits. Something like x & ((~x) +1) will give you the value of the last bit that is set, mask it out and repeat. If you need to do it a lot, build a table of 256 values and then process 8 bits at a time. Should be fairly straight forward... Hope this helps, -- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a > tool for doing 5% of the work and then sitting around waiting for someone > else to do the other 95% so you can sue them.
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