Computing Hamming weight, also called popcount in Java?

Question

I am not sure how to translate this from C++ to Java. It is a function that computes the Hamming weight.

/** This is popcount_3() from:
 * http://en.wikipedia.org/wiki/Hamming_weight */
unsigned int popcnt32(uint32_t n) const
{
    n -= ((n >> 1) & 0x55555555);
    n = (n & 0x33333333) + ((n >> 2) & 0x33333333);
    return (((n + (n >> 4))& 0xF0F0F0F)* 0x1010101) >> 24;
}

More concretely, I don't know what to use instead of uint32_t, and if I use that type whatever it is, can I just leave the rest code unchanged?

Thanks

For one, there is no equivalent of `uint32_t` in Java, you'd have to use `long`. — fge, Jan 12 '13 at 20:33
Oli well I am not sure what to try really. It seems like so many things can go wrong. — user1796942, Jan 12 '13 at 20:34
@fge: An `int` should work fine, although some of the operators may need to change a little... — Oliver Charlesworth, Jan 12 '13 at 20:43
Change the first line to `static int popcnt32(int n)`. The rest can stay as is, although using `>>>` instead of `>>` in some places could be considered cleaner. — Daniel Fischer, Jan 12 '13 at 21:30

score 18 · Accepted Answer · edited Jan 09 '15 at 07:54

18

It's implemented for you in Integer.bitCount(int i)

edited Jan 09 '15 at 07:54

Alex D

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answered Jan 12 '13 at 20:36

zch

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Computing Hamming weight, also called popcount in Java?

1 Answers1