Sign Extend Accumulator Into rDX

Encoding

Description

The CWD/CDQ/CQO instructions sign extend the accumulator into the data register (rDX). This essentially sets every bit of the data register to that of the accumulator.

This instruction is similar to CBW/CWDE/CDQE (Sign Extend Accumulator), but working into the data register.

Operation

public void CWD()
{
    // DX:AX = SignExtend(AX)
    DX = AX.Bit[15] ? 0xFFFF : 0;
}

public void CDQ()
{
    // EDX:EAX = SignExtend(EAX)
    EDX = EAX.Bit[31] ? 0xFFFFFFFF : 0;
}

public void CQO()
{
    // RDX:RAX = SignExtend(RAX)
    RDX = RAX.Bit[63] ? 0xFFFFFFFFFFFFFFFF : 0;
}

Flags Affected

Exceptions

Real-Address Mode

Virtual-8086 Mode

Protected Mode

Compatibility Mode

Long Mode