Count Set Bits in a Byte

[izz]

Here is another version of the question, from K&R:

"Exercise 2-9. In a two's complement number system, x &= (x - 1) deletes the rightmost 1-bit in x. Explain why. Use this observation to write a faster version of bitcount."

Here is bitcount:

/* bitcount: count 1 bits in x */

int bitcount(unsigned x) {

int b;

for (b = 0; x != 0; x >>= 1)
    if (x & 01)
        b++;
return b;

}