public static ushort GetInstructionValue(Cpu8086 cpu, OpCodeManager.OpCodeFlag flag, Register segmentPrefix, int instruction, int instructionValue, int instructionDisplacement)
{
switch (instruction)
{
case (int)Register.AX:
case (int)Register.CX:
case (int)Register.DX:
case (int)Register.BX:
case (int)Register.SP:
case (int)Register.BP:
case (int)Register.SI:
case (int)Register.DI:
case (int)Register.IP:
case (int)Register.CS:
case (int)Register.DS:
case (int)Register.ES:
case (int)Register.SS:
return(cpu.GetRegister((Register)instruction));
case OpCodeManager.ARG_BYTE_REGISTER:
return(cpu.GetRegisterU8((Register)instructionValue));
case OpCodeManager.ARG_DEREFERENCE:
case OpCodeManager.ARG_MEMORY:
var address = GetInstructionRealAddress(cpu, segmentPrefix, instruction, instructionValue, instructionDisplacement);
return(flag.Has(OpCodeManager.OpCodeFlag.Size8) ? cpu.ReadU8(address) : cpu.ReadU16(address));
case OpCodeManager.ARG_CONSTANT:
return((ushort)instructionValue);
default:
throw new NotImplementedException();
}
}
public static void CalculateSubFlags(Cpu8086 cpu, OpCodeManager.OpCodeFlag flag, ushort value1, ushort value2, int result)
{
if (flag.Has(OpCodeManager.OpCodeFlag.Size8))
{
CalculateSubFlags8Bit(cpu, (byte)value1, (byte)value2, result);
}
else
{
CalculateSubFlags16Bit(cpu, value1, value2, result);
}
}
public static void CalculateBitwiseFlags16Bit(Cpu8086 cpu, ushort value1, ushort value2, int result)
{
var truncResult = (ushort)result;
var sign = ((truncResult >> 15) & 1) == 1;
var zero = truncResult == 0;
var parity = ParityLookup[(byte)(result & 0xFF)];
cpu.Flags &= ~(FlagsRegister.Carry | FlagsRegister.Parity | FlagsRegister.Zero | FlagsRegister.Sign | FlagsRegister.Overflow);
cpu.Flags |= (parity ? FlagsRegister.Parity : 0) |
(zero ? FlagsRegister.Zero : 0) |
(sign ? FlagsRegister.Sign : 0);
}
public static ushort GetInstructionAddress(Cpu8086 cpu, int instruction, int instructionValue, int instructionDisplacement)
{
switch (instruction)
{
case OpCodeManager.ARG_DEREFERENCE:
ushort address;
switch (instructionValue)
{
case 0:
address = (ushort)(cpu.GetRegister(Register.BX) + cpu.GetRegister(Register.SI));
break;
case 1:
address = (ushort)(cpu.GetRegister(Register.BX) + cpu.GetRegister(Register.DI));
break;
case 2:
address = (ushort)(cpu.GetRegister(Register.BP) + cpu.GetRegister(Register.SI));
break;
case 3:
address = (ushort)(cpu.GetRegister(Register.BP) + cpu.GetRegister(Register.DI));
break;
case 4:
address = cpu.GetRegister(Register.SI);
break;
case 5:
address = cpu.GetRegister(Register.DI);
break;
case 6:
address = cpu.GetRegister(Register.BP);
break;
case 7:
address = cpu.GetRegister(Register.BX);
break;
default:
throw new NotImplementedException();
}
return((ushort)(address + instructionDisplacement));
case OpCodeManager.ARG_MEMORY:
return((ushort)instructionValue);
default:
throw new NotImplementedException();
}
}
public static void CalculateDecFlags16Bit(Cpu8086 cpu, ushort value1, ushort value2, int result)
{
var truncResult = (ushort)result;
var sign = ((truncResult >> 15) & 1) == 1;
var overflow = ((truncResult ^ value1) & (value1 ^ value2) & 0x8000) == 0x8000;
var auxiliary = ((value1 ^ value2 ^ truncResult) & 0x10) != 0;
var zero = truncResult == 0;
var parity = ParityLookup[(byte)(result & 0xFF)];
cpu.Flags &= ~(FlagsRegister.Parity | FlagsRegister.Auxiliary | FlagsRegister.Zero | FlagsRegister.Sign | FlagsRegister.Overflow);
cpu.Flags |= (parity ? FlagsRegister.Parity : 0) |
(auxiliary ? FlagsRegister.Auxiliary : 0) |
(zero ? FlagsRegister.Zero : 0) |
(sign ? FlagsRegister.Sign : 0) |
(overflow ? FlagsRegister.Overflow : 0);
}
public static void CalculateAddFlags8Bit(Cpu8086 cpu, byte value1, byte value2, int result)
{
var truncResult = (byte)result;
var carry = (uint)result > 0xFF;
var sign = ((truncResult >> 7) & 1) == 1;
var overflow = ((truncResult ^ value1) & (truncResult ^ value2) & 0x80) == 0x80;
var auxiliary = ((value1 ^ value2 ^ truncResult) & 0x10) != 0;
var zero = truncResult == 0;
var parity = ParityLookup[(byte)(result & 0xFF)];
cpu.Flags &= ~(FlagsRegister.Carry | FlagsRegister.Parity | FlagsRegister.Auxiliary | FlagsRegister.Zero | FlagsRegister.Sign | FlagsRegister.Overflow);
cpu.Flags |= (carry ? FlagsRegister.Carry : 0) |
(parity ? FlagsRegister.Parity : 0) |
(auxiliary ? FlagsRegister.Auxiliary : 0) |
(zero ? FlagsRegister.Zero : 0) |
(sign ? FlagsRegister.Sign : 0) |
(overflow ? FlagsRegister.Overflow : 0);
}
public static uint GetInstructionRealAddress(Cpu8086 cpu, Register segmentPrefix, int instruction, int instructionValue, int instructionDisplacement)
{
switch (instruction)
{
case OpCodeManager.ARG_DEREFERENCE:
if (segmentPrefix == Register.Invalid)
{
segmentPrefix = instructionValue == 6 ? Register.SS : Register.DS; // BP needs SS segment
}
var addr = GetInstructionAddress(cpu, instruction, instructionValue, instructionDisplacement);
return(SegmentToAddress(cpu.GetRegister(segmentPrefix), addr));
case OpCodeManager.ARG_MEMORY:
if (segmentPrefix == Register.Invalid)
{
segmentPrefix = Register.DS;
}
var address = GetInstructionAddress(cpu, instruction, instructionValue, instructionDisplacement);
return(SegmentToAddress(cpu.GetRegister(segmentPrefix), address));
default:
throw new NotImplementedException();
}
}
public Fetcher8086(Cpu8086 cpu)
{
_cpu = cpu;
_fetched = 0;
}