/// <summary>
        /// Writes an instruction's opcode
        /// </summary>
        /// <param name="writer">The instruction writer</param>
        /// <param name="instr">The instruction</param>
        protected void WriteOpCode(ref ArrayWriter writer, Instruction instr)
        {
            var code = instr.OpCode.Code;
            var hi   = (ushort)code >> 8;

            if ((ushort)code <= 0xFF)
            {
                writer.WriteByte((byte)code);
            }
            else if (hi == 0xFE || (hi >= 0xF0 && hi <= 0xFB))
            {
                writer.WriteByte((byte)((ushort)code >> 8));
                writer.WriteByte((byte)code);
            }
            else if (code == Code.UNKNOWN1)
            {
                writer.WriteByte((byte)Code.Nop);
            }
            else if (code == Code.UNKNOWN2)
            {
                writer.WriteUInt16((ushort)(((ushort)Code.Nop << 8) | Code.Nop));
            }
            else
            {
                Error("Unknown instruction");
                writer.WriteByte((byte)Code.Nop);
            }
        }
        /// <summary>
        /// Writes an <see cref="OperandType.InlineVar"/> operand
        /// </summary>
        /// <param name="writer">Instruction writer</param>
        /// <param name="instr">Instruction</param>
        protected virtual void WriteInlineVar(ref ArrayWriter writer, Instruction instr)
        {
            var variable = instr.Operand as IVariable;

            if (variable is null)
            {
                Error("Operand is not a local/arg");
                writer.WriteUInt16(0);
            }
            else
            {
                int index = variable.Index;
                if (ushort.MinValue <= index && index <= ushort.MaxValue)
                {
                    writer.WriteUInt16((ushort)index);
                }
                else
                {
                    Error("Local/arg index doesn't fit in a UInt16");
                    writer.WriteUInt16(0);
                }
            }
        }