Steve's 'Cute Code' collection shows a loopless trick to "Count the number of '1' bits in a 32 bit word":[edit]This has come up here a couple times, too.Code:n = (n & 0x55555555) + ((n & 0xaaaaaaaa) >> 1); n = (n & 0x33333333) + ((n & 0xcccccccc) >> 2); n = (n & 0x0f0f0f0f) + ((n & 0xf0f0f0f0) >> 4); n = (n & 0x00ff00ff) + ((n & 0xff00ff00) >> 8); n = (n & 0x0000ffff) + ((n & 0xffff0000) >> 16);
Last edited by Dave_Sinkula; 09-20-2004 at 12:44 PM.
7. It is easier to write an incorrect program than understand a correct one.
40. There are two ways to write error-free programs; only the third one works.*
You could use a lookup table if you want it faster.Originally Posted by Dave_Sinkula
Quzah.
Hope is the first step on the road to disappointment.
Code:n = (n & 0x55555555) + ((n & 0xaaaaaaaa) >> 1); n = (n & 0x33333333) + ((n & 0xcccccccc) >> 2); n = (n & 0x0f0f0f0f) + ((n & 0xf0f0f0f0) >> 4); n = (n & 0x00ff00ff) + ((n & 0xff00ff00) >> 8); n = (n & 0x0000ffff) + ((n & 0xffff0000) >> 16);
Can anybody explain, how does this work?
