c - Count bits in the number

Duplicate:

href="https://stackoverflow.com/questions/109023/best-algorithm-to-count-the-number-of-set-bits-in-a-32-bit-integer">Best
algorithm to count the number of set bits in a 32-bit
integer?

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Suppose you have a number. Is there any way to count
the bits which equals to 1 in binary representation of that number, not using iteration?
I mean, is there any way to do it in constant time using some bitwise operators and
masks. I need solution which will work well for both architectures 32 bit and 64 bit. Ah
almost forgot, I need it for C language or assembler is also good.

Answer

There is a bit counting algorithm without a
loop at http://graphics.stanford.edu/~seander/bithacks.html. Lots of
bit counting algorithms at href="http://gurmeetsingh.wordpress.com/2008/08/05/fast-bit-counting-routines/"
rel="nofollow
noreferrer">http://gurmeetsingh.wordpress.com/2008/08/05/fast-bit-counting-routines/