private static void ParseArgument([NotNull] IInstructionFetcher fetcher, OpCodeFlag flag, out int argument, out int argumentValue, out int argumentDisplacement, int argumentType, byte modrm)
{
var mod = (byte)((modrm >> 6) & 7);
var reg = (byte)((modrm >> 3) & 7);
var rm = (byte)(modrm & 7);
switch (argumentType)
{
case ARG_AX:
case ARG_CX:
case ARG_DX:
case ARG_BX:
case ARG_SP:
case ARG_BP:
case ARG_SI:
case ARG_DI:
case ARG_IP:
case ARG_CS:
case ARG_DS:
case ARG_ES:
case ARG_SS:
case ARG_FLAGS:
argument = argumentType;
argumentValue = ARG_NONE;
argumentDisplacement = ARG_NONE;
break;
case ARG_AL:
case ARG_CL:
case ARG_DL:
case ARG_BL:
case ARG_AH:
case ARG_CH:
case ARG_DH:
case ARG_BH:
argument = ARG_BYTE_REGISTER;
argumentValue = argumentType;
argumentDisplacement = ARG_NONE;
break;
case ARG_1:
argument = ARG_CONSTANT;
argumentValue = 1;
argumentDisplacement = ARG_NONE;
break;
case ARG_3:
argument = ARG_CONSTANT;
argumentValue = 3;
argumentDisplacement = ARG_NONE;
break;
case ARG_IB:
argument = ARG_CONSTANT;
argumentValue = fetcher.FetchU8();
argumentDisplacement = ARG_NONE;
if (flag.Has(OpCodeFlag.Signed))
{
argumentValue = (sbyte)(byte)argumentValue;
}
break;
case ARG_IW:
argument = ARG_CONSTANT;
argumentValue = fetcher.FetchU16();
argumentDisplacement = ARG_NONE;
break;
case ARG_JB:
argument = ARG_CONSTANT;
argumentValue = (sbyte)fetcher.FetchU8();
argumentDisplacement = ARG_NONE;
break;
case ARG_JW:
argument = ARG_CONSTANT;
argumentValue = fetcher.FetchU16();
argumentDisplacement = ARG_NONE;
break;
case ARG_S:
Debug.Assert(reg < 4);
argument = reg + ARG_ES;
argumentValue = ARG_NONE;
argumentDisplacement = ARG_NONE;
break;
case ARG_GB:
argument = ARG_BYTE_REGISTER;
argumentValue = ARG_AL + reg;
argumentDisplacement = ARG_NONE;
break;
case ARG_GW:
argument = reg;
argumentValue = ARG_NONE;
argumentDisplacement = ARG_NONE;
break;
case ARG_OB:
case ARG_OW:
argument = ARG_MEMORY;
argumentValue = fetcher.FetchU16();
argumentDisplacement = ARG_NONE;
break;
case ARG_A:
argument = ARG_FAR_MEMORY;
var address = fetcher.FetchU16();
var segment = fetcher.FetchU16();
argumentValue = (int)(((uint)segment << 16) | address);
argumentDisplacement = ARG_NONE;
break;
case ARG_EB:
case ARG_EW:
case ARG_M:
switch (mod)
{
case 0:
if (rm == 6)
{
argument = ARG_MEMORY;
argumentValue = fetcher.FetchU16();
argumentDisplacement = ARG_NONE;
}
else
{
argument = ARG_DEREFERENCE;
argumentValue = rm;
argumentDisplacement = 0;
}
break;
case 1:
argument = ARG_DEREFERENCE;
argumentValue = rm;
argumentDisplacement = (sbyte)fetcher.FetchU8();
break;
case 2:
argument = ARG_DEREFERENCE;
argumentValue = rm;
argumentDisplacement = fetcher.FetchU16();
break;
case 3:
Debug.Assert(argumentType != ARG_M);
if (argumentType == ARG_EB)
{
argument = ARG_BYTE_REGISTER;
argumentValue = ARG_AL + rm;
}
else
{
argument = rm;
argumentValue = ARG_NONE;
}
argumentDisplacement = ARG_NONE;
break;
default:
throw new NotImplementedException();
}
break;
case ARG_NONE:
argument = ARG_NONE;
argumentValue = ARG_NONE;
argumentDisplacement = ARG_NONE;
break;
default:
throw new NotImplementedException();
}
}
public static Instruction Decode([NotNull] IInstructionFetcher fetcher)
{
Instruction instruction;
var opcode = fetcher.FetchU8();
instruction.Type = opCodes[opcode].Type;
instruction.SegmentPrefix = Cpu8086.Register.Invalid;
instruction.OpcodePrefix = 0;
while (instruction.Type == InstructionType.Prefix)
{
switch (opcode)
{
case 0x26:
instruction.SegmentPrefix = Cpu8086.Register.ES;
break;
case 0x2E:
instruction.SegmentPrefix = Cpu8086.Register.CS;
break;
case 0x36:
instruction.SegmentPrefix = Cpu8086.Register.SS;
break;
case 0x3E:
instruction.SegmentPrefix = Cpu8086.Register.DS;
break;
case 0xF0:
case 0xF2:
case 0xF3:
instruction.OpcodePrefix = opcode;
break;
default:
throw new NotImplementedException();
}
opcode = fetcher.FetchU8();
instruction.Type = opCodes[opcode].Type;
}
if (instruction.Type == InstructionType.EmulatorSpecial)
{
var opcode2 = fetcher.FetchU8();
Debug.Assert(opcode2 == 0x0F);
}
Debug.Assert(instruction.Type != InstructionType.Invalid);
var argument1Type = opCodes[opcode].Argument1Type;
var argument2Type = opCodes[opcode].Argument2Type;
instruction.Flag = opCodes[opcode].Flag;
byte rm = 0xFF;
if (instruction.Flag.Has(OpCodeFlag.HasRM))
{
rm = fetcher.FetchU8();
}
if (instruction.Type == InstructionType.Group)
{
instruction.Type = ConvertFromGroup(opcode, rm);
Debug.Assert(instruction.Type != InstructionType.Invalid);
var reg = (byte)((rm >> 3) & 7);
if (opcode == 0xF6 && reg == 0)
{
argument2Type = ARG_IB;
}
else if (opcode == 0xF7 && reg == 0)
{
argument2Type = ARG_IW;
}
else if (opcode == 0xFF && (reg == 3 || reg == 5))
{
argument1Type = ARG_M;
}
}
ParseArgument(fetcher, instruction.Flag, out instruction.Argument1, out instruction.Argument1Value, out instruction.Argument1Displacement, argument1Type, rm);
ParseArgument(fetcher, instruction.Flag, out instruction.Argument2, out instruction.Argument2Value, out instruction.Argument2Displacement, argument2Type, rm);
return(instruction);
}