type instArgs … type instFormat … var errShort … var errUnknown … var decoderCover … func init() { … } // Decode decodes the 4 bytes in src as a single instruction. func Decode(src []byte) (inst Inst, err error) { … } // decodeArg decodes the arg described by aop from the instruction bits x. // It returns nil if x cannot be decoded according to aop. func decodeArg(aop instArg, x uint32, index int) Arg { … }