# INC — Increment by 1

## Description

Adds 1 to the destination operand, while preserving the state of the CF flag. The destination operand can be a register or a memory location.
This instruction allows a loop counter to be updated without disturbing the CF flag. Use a ADD instruction with an immediate operand of 1 to
perform an increment operation that does updates the CF flag.

## Instruction

| Opcode        | Assembly  | Op/En | Modern Mode | Legacy Mode | Description                                                                  |
|---------------|-----------|-------|-------------|-------------|------------------------------------------------------------------------------|
| FE /0         | INC r/m8  | M     | Valid       | Valid       | Increment r/m byte by 1.                                                     |
| REX + FE /0   | INC r/m8* | M     | Valid       | N.E.        | Increment r/m byte by 1.                                                     |
| FF /0         | INC r/m16 | M     | Valid       | Valid       | Increment r/m word by 1.                                                     |
| FF /0         | INC r/m32 | M     | Valid       | Valid       | Increment r/m doubleword by 1.                                               |
| REX.W + FF /0 | INC r/m64 | M     | Valid       | N.E.        | Increment r/m quadword by 1.                                                 |
| 40+ rw**      | INC r16   | O     | N.E.        | Valid       | Increment word register by 1.                                                |
| 40+ rd        | INC r32   | O     | N.E.        | Valid       | Increment doubleword register by 1.                                          |

- In 64-bit mode, r/m8 can not be encoded to access the following byte registers if a REX prefix is used: AH, BH, CH, DH.

- 40H through 47H are REX prefixes in 64-bit mode.

## Information

This instruction can be used with a LOCK prefix to allow the instruction to be executed atomically.

In 64-bit mode, INC r16 and INC r32 are not encodable (because opcodes 40H through 47H are REX prefixes). Otherwise, the instruction’s 64-bit
mode default operation size is 32 bits. Use of the REX.R prefix permits access to additional registers (R8-R15). Use of the REX.W prefix
promotes operation to 64 bits.