func HostTo(endian Endianness, dst Register, size Size) Instruction {
	var imm int64
	switch size {
	case Half:
		imm = 16
	case Word:
		imm = 32
	case DWord:
		imm = 64
	default:
		return Instruction{OpCode: InvalidOpCode}
	}
	return Instruction{
		OpCode:   OpCode(ALUClass).SetALUOp(Swap).SetSource(Source(endian)),
		Dst:      dst,
		Constant: imm,
	}
}
HostTo converts from host to another endianness.
package asm
type Source uint8
const sourceMask OpCode = 0x08
const (
	InvalidSource Source = 0xff
	ImmSource Source = 0x00
	RegSource Source = 0x08
)
type Endianness uint8
const endianMask = sourceMask
const (
	InvalidEndian Endianness = 0xff
	LE Endianness = 0x00
	BE Endianness = 0x08
)
type ALUOp uint8
const aluMask OpCode = 0xf0
const (
	InvalidALUOp ALUOp = 0xff
	Add ALUOp = 0x00
	Sub ALUOp = 0x10
	Mul ALUOp = 0x20
	Div ALUOp = 0x30
	Or ALUOp = 0x40
	And ALUOp = 0x50
	LSh ALUOp = 0x60
	RSh ALUOp = 0x70
	Neg ALUOp = 0x80
	Mod ALUOp = 0x90
	Xor ALUOp = 0xa0
	Mov ALUOp = 0xb0
	ArSh ALUOp = 0xc0
	Swap ALUOp = 0xd0
)