# 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.