cbtw
sign-extend AL -> AX
cbtw converts the signed byte in AL to a signed word in AX by extending the most-significant bit (sign bit) of AL into all bits of AH.
cbtw
cwtl
sign-extend AX -> EAX
cwtl converts the signed word in AX to a signed long in EAX by extending the most-significant bit (sign bit) of AX into two most-significant bytes of EAX.
cwtl
cwtd
sign-extend AX -> DX:AX
cwtd converts the signed word in AX to a signed double word in DX:AX by extending the most-significant bit (sign bit) of AX into all bits of DX.
cwtd
cltd
sign-extend EAX -> EDX:EAX
cltd converts the signed long in EAX to a signed double long in EDX:EAX by extending the most-significant bit (sign bit) of EAX into all bits of EDX.
cltd