CMC (Complement Carry Flag)

Opcodes

Opcode Instruction Op/En 64-bit Mode Compat/Leg Mode Description
F5 CMC NP Valid Valid Complement CF flag.

Instruction Operand Encoding

Op/En Operand 1 Operand 2 Operand 3 Operand 4
NP NA NA NA NA

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.