code: func Len(v int64) int {
  	u := uint64(v)
  	switch {
  	case u < 0x80:
  		return 1
  	case u < 0x4000:
  		return 2
  	case u < 0x200000:
  		return 3
  	case u < 0x10000000:
  		return 4
  	case u < 0x800000000:
  		return 5
  	case u < 0x40000000000:
  		return 6
  	case u < 0x2000000000000:
  		return 7
  	case u < 0x100000000000000:
  		return 8
  	default:
  		return 9
  	}
  }
docs: // Len returns the number of bytes required to encode v.