C code to count the number of '1' bits in an unsigned char

Question

I need C code to return the number of 1\'s in an unsigned char in C. I need an explanation as to why it works if it\'s not obvious. I\'ve found a lot of code for a 32-bit nu

Answer 1

const unsigned char oneBits[] = {0,1,1,2,1,2,2,3,1,2,2,3,2,3,3,4};

unsigned char CountOnes(unsigned char x)
{
    unsigned char results;
    results = oneBits[x&0x0f];
    results += oneBits[x>>4];
    return results
}

Have an array that knows the number of bits for 0 through 15. Add the results for each nibble.

Answer 2

See the bit twiddling hacks page: http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetKernighan

there are many good solutions for this.

Also, this function in its simplest implementation is fairly trivial. You should take the time to learn how to do this.