RegisterPrefix map[string]bool
	// RegisterNumber converts R(10) into arm.REG_R10.
	RegisterNumber func(string, int16) (int16, bool)
	// Instruction is a jump.
	IsJump func(word string) bool
}

// nilRegisterNumber is the register number function for architectures
// that do not accept the R(N) notation. It always returns failure.
func nilRegisterNumber(name string, n int16) (int16, bool) {

	p.addr = p.addr[0:0]
	p.isJump = p.arch.IsJump(word)
	for _, op := range operands {
		addr := p.address(op)
		if !p.isJump && addr.Reg < 0 { // Jumps refer to PC, a pseudo.
			p.errorf("illegal use of pseudo-register in %s", word)
		}
		p.addr = append(p.addr, addr)
	}
	if p.isJump {
		p.asmJump(op, cond, p.addr)
		return
	}
	p.asmInstruction(op, cond, p.addr)