code: func pop_array(arr []int64) int {
  	popCount := 0
  	for _, v := range arr {
  		uv := uint64(v)
  		for uv > 0 {
  			popCount += BitCount(byte(uv & 0xff))
  			uv >>= 8
  		}
  	}
  	return popCount
  }
docs: /* Returns the number of set bits in a slice of int64. */