func (dec *Decoder) decodeMap(mtyp reflect.Type, state *decoderState, value reflect.Value, keyOp, elemOp decOp, ovfl error) {
	n := int(state.decodeUint())
	if value.IsNil() {
		value.Set(reflect.MakeMapWithSize(mtyp, n))
	}
	keyIsPtr := mtyp.Key().Kind() == reflect.Pointer
	elemIsPtr := mtyp.Elem().Kind() == reflect.Pointer
	keyInstr := &decInstr{keyOp, 0, nil, ovfl}
	elemInstr := &decInstr{elemOp, 0, nil, ovfl}