+ ULONG FirstValue = State->GeneralRegs[SOFT386_REG_EAX].Long;
+ ULONG SecondValue = 0;
+ ULONG Result;
+ ULONG DataSize, DataMask, SignFlag;
+ BOOLEAN OperandSize, AddressSize;
+
+ OperandSize = AddressSize = State->SegmentRegs[SOFT386_REG_CS].Size;
+
+ /* Make sure this is the right instruction */
+ ASSERT((Opcode & 0xFE) == 0xAE);
+
+ if (State->PrefixFlags & SOFT386_PREFIX_OPSIZE)
+ {
+ /* The OPSIZE prefix toggles the size */
+ OperandSize = !OperandSize;
+ }
+
+ if (State->PrefixFlags & SOFT386_PREFIX_ADSIZE)
+ {
+ /* The ADSIZE prefix toggles the size */
+ AddressSize = !AddressSize;
+ }
+
+ if ((State->PrefixFlags & SOFT386_PREFIX_REP)
+ || (State->PrefixFlags & SOFT386_PREFIX_REPNZ))
+ {
+ // TODO: The REP/REPZ/REPNZ prefixes need to be implemented!
+ Soft386Exception(State, SOFT386_EXCEPTION_UD);
+ return FALSE;
+ }
+
+ /* Calculate the size */
+ if (Opcode == 0xA6) DataSize = sizeof(UCHAR);
+ else DataSize = OperandSize ? sizeof(ULONG) : sizeof(USHORT);
+
+ /* Calculate the mask and sign flag */
+ DataMask = (1 << (DataSize * 8)) - 1;
+ SignFlag = 1 << ((DataSize * 8) - 1);
+
+ /* Read from the source operand */
+ if (!Soft386ReadMemory(State,
+ SOFT386_REG_ES,
+ AddressSize ? State->GeneralRegs[SOFT386_REG_EDI].Long
+ : State->GeneralRegs[SOFT386_REG_EDI].LowWord,
+ FALSE,
+ &SecondValue,
+ DataSize))
+ {
+ /* Exception occurred */
+ return FALSE;
+ }
+
+ /* Calculate the result */
+ FirstValue &= DataMask;
+ SecondValue &= DataMask;
+ Result = (FirstValue - SecondValue) & DataMask;
+
+ /* Update the flags */
+ State->Flags.Cf = FirstValue < SecondValue;
+ State->Flags.Of = ((FirstValue & SignFlag) != (SecondValue & SignFlag))
+ && ((FirstValue & SignFlag) != (Result & SignFlag));
+ State->Flags.Af = (FirstValue & 0x0F) < (SecondValue & 0x0F);
+ State->Flags.Zf = (Result == 0) ? TRUE : FALSE;
+ State->Flags.Sf = (Result & SignFlag) ? TRUE : FALSE;
+ State->Flags.Pf = Soft386CalculateParity(Result);
+
+ /* Increment/decrement EDI */
+ if (OperandSize)
+ {
+ if (State->Flags.Df) State->GeneralRegs[SOFT386_REG_EDI].Long += DataSize;
+ else State->GeneralRegs[SOFT386_REG_EDI].Long -= DataSize;
+ }
+ else
+ {
+ if (State->Flags.Df) State->GeneralRegs[SOFT386_REG_EDI].LowWord += DataSize;
+ else State->GeneralRegs[SOFT386_REG_EDI].LowWord -= DataSize;
+ }
+
+ /* Return success */
+ return TRUE;