统计uint64的数对应二进制数的1的个数

// pc[i] is the populatio count of i
var pc [256]byte

//统计出o~255每个数对应二进制上1的个数
func init() {
   for i := range pc {
       pc[i] = pc[i/2] + byte(i&1)
       // fmt.Printf("i = %d, pc[%d] = %d, pc[%d] = %d, byte(%d&1) = %d ",
           i, i, pc[i], i/2, pc[i/2], i, byte(i&1))
   }
}

// PopCount return the population count (number of set bits) of x.
//将x分部分左移到底八位(0~255)
func PopCount(x uint64) int {
   return int(pc[byte(x>>(0*8))] +
       pc[byte(x>>(1*8))] +
       pc[byte(x>>(2*8))] +
       pc[byte(x>>(3*8))] +
       pc[byte(x>>(4*8))] +
       pc[byte(x>>(5*8))] +
       pc[byte(x>>(6*8))] +
       pc[byte(x>>(7*8))])
}
func init() {
   for i := range pc {
       pc[i] = pc[i/2] + byte(i&1)
       fmt.Printf("i = %d, pc[%d] = %d, pc[%d] = %d, byte(%d&1) = %d ",
           i, i, pc[i], i/2, pc[i/2], i, byte(i&1))
   }
}

// PopCount return the population count (number of set bits) of x.

func PopCount(x uint64) int {
   return int(pc[byte(x>>(0*8))] +
       pc[byte(x>>(1*8))] +
       pc[byte(x>>(2*8))] +
       pc[byte(x>>(3*8))] +
       pc[byte(x>>(4*8))] +
       pc[byte(x>>(5*8))] +
       pc[byte(x>>(6*8))] +
       pc[byte(x>>(7*8))])
}