package x64

// regReg encodes an operation using 2 registers.
func regReg(code []byte, reg byte, rm byte, opCodes ...byte) []byte {
	w := byte(1)      // Indicates a 64-bit register.
	r := byte(0)      // Extension to the "reg" field in ModRM.
	x := byte(0)      // Extension to the SIB index field.
	b := byte(0)      // Extension to the "rm" field in ModRM or the SIB base (r8 up to r15 use this).
	mod := byte(0b11) // Direct addressing mode, no register offsets.

	if reg > 0b111 {
		r = 1
		reg &= 0b111
	}

	if rm > 0b111 {
		b = 1
		rm &= 0b111
	}

	rex := REX(w, r, x, b)
	modRM := ModRM(mod, reg, rm)

	code = append(code, rex)
	code = append(code, opCodes...)
	code = append(code, modRM)

	return code
}