CMC - Complement Carry Flag

Opcode

Instruction

Op/ En

64-bit Mode

Compat/ Leg Mode

Description

F5

CMC

ZO

Valid

Valid

Complement CF flag.

Instruction Operand Encoding

Op/En

Operand 1

Operand 2

Operand 3

Operand 4

ZO

N/A

N/A

N/A

N/A

Description

Complements the CF flag in the EFLAGS register. CMC operation is the same in non-64-bit modes and 64-bit mode.

Operation 

EFLAGS.CF[bit 0] := NOT EFLAGS.CF[bit 0];

Flags Affected

The CF flag contains the complement of its original value. The OF, ZF, SF, AF, and PF flags are unaffected.

Exceptions (All Operating Modes)

#UD

If the LOCK prefix is used.