buf.WriteString(arg.String())
	}
	return buf.String()
}

// An Op is an instruction operation.
type Op uint16

func (o Op) String() string {
	if int(o) >= len(opstr) || opstr[o] == "" {
		return fmt.Sprintf("Op(%d)", int(o))
	}
	return opstr[o]
}

// An Arg is a single instruction argument, one of these types: Reg, CondReg, SpReg, Imm, PCRel, Label, or Offset.
type Arg interface {
	IsArg()
	String() string
}

// are not a dense packing from 0 to N, although the
// density is high, probably at least 90%.

func (op Op) String() string {
	if op >= Op(len(opstr)) || opstr[op] == "" {
		return fmt.Sprintf("Op(%d)", int(op))
	}
	return opstr[op]
}

// An Inst is a single instruction.
type Inst struct {
	Op   Op     // Opcode mnemonic
	Enc  uint32 // Raw encoding bits.