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80386 Programmer's Reference Manual -- Opcode CWD |
CWD/CDQ -- Convert Word to Doubleword/Convert Doubleword to Quadword
OperationIF OperandSize = 16 (* CWD instruction *) THEN IF AX < 0 THEN DX := 0FFFFH; ELSE DX := 0; FI; ELSE (* OperandSize = 32, CDQ instruction *) IF EAX < 0 THEN EDX := 0FFFFFFFFH; ELSE EDX := 0; FI; FI; DescriptionCWD converts the signed word in AX to a signed doubleword in DX:AX by extending the most significant bit of AX into all the bits of DX. CDQ converts the signed doubleword in EAX to a signed 64-bit integer in the register pair EDX:EAX by extending the most significant bit of EAX (the sign bit) into all the bits of EDX. Note that CWD is different from CWDE. CWDE uses EAX as a destination, instead of DX:AX.Flags AffectedNoneProtected Mode ExceptionsNoneReal Address Mode ExceptionsNoneVirtual 8086 Mode ExceptionsNone
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