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#include <stdio.h>
/* counts 1-bits in x */
int bitcount(unsigned x);
int main(int argc, char *argv[]) { return 0; }
int bitcount(unsigned x) {
// Explanation: on a two's complement system, x - 1 is performed by
// adding the two's complement of 1 (i.e. 111...1) to x. Adding 1 to
// the rightmost 1-bit results in 0 which when &-ed with x, results in 0.
int b;
for (b = 0; x != 0; x &= (x - 1))
b++;
return b;
}
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